What is a Polytunnel?

A polytunnel is most commonly an elongated semi curcular shaped tunnel made out of polyethylene. They come in a wide variety of shapes and sizes. In functionality they fall somewhere between a garden cloche and a greenhouse, a cloche is used for the same effect with single plants while a greenhouse is much larger and often made out of glass. The polytunnels main use is to create a sort of microclimate that provides higher temperatures and humidity allowing you to grow various fruit and vegetable plants even when they are out of season. They are also an excellent form of crop protection, protecting plants from heat, cold, wind, rain and strong sunlight. Another major benefit of having a polytunnel is that they are not a permanent structure and can be moved about or taken down completely, quite easily. Smaller polytunnels or hobby tunnels can be used as a kitchen garden for herbs and salads, and larger ones can be used for anything, from growing entire vegetable crops to plant and flower nurseries.

Why Use a Polytunnel?

Most importantly, a polytunnel will enable the gardener to grow fruit and vegetable plants that they would otherwise be unable to grow in their climate. They also extend your growing season so you can grow your favourite foods all year round. Temperatures, humidity, irrigation and ventilation can all be easily controlled via the wide range of polytunnel equipment commonly available. Polytunnels work out much cheaper to buy, maintain and install than greenhouses and are quite easy to put up and manoeuvre yourself. The polyethylene or polythene film most commonly used biodegrades naturally over a long period. It will generally last between 3 to 10 years depending on usage and site etc, before needing replacement.

What To Grow in a Polytunnel

Basically all kinds of flowers, fruit and vegetable plants can be grown. 80% of all soft fruits on the market are grown in polytunnels.

Here is a list of plants commonly grown in a polytunnel: tomatoes, strawberries, potatoes, cucumbers, peppers, salad greens, radish, carrots, melons, cauliflower, lettuce, chillis, peas & beans, cabbage, oriental salads, onions

Growing in a Polytunnel

First off you need to think about positioning.
Polytunnels need:

  • Flat, even ground
  • Access to a decent water supply
  • A nice sunny area with some shade (next to a wall or hedge)
  • Try and position it N/S instead of E/W to minimize the amount of direct heat from the sun.

Most polytunnels are spacious enough for two rows of raised beds inside, this is ideal as you won’t have to walk over good soil to tend plants. Use good quality soil. Raised beds make it easy to maintain a good soil structure. Try and alter your sowing dates to maximize your polytunnels output and to ensure there is always something to harvest.

Pests in the polytunnel

Polytunnels offer excellent pest protection for crops, but you can never be 100% pest free. As a preventative measure keep your tunnel well ventilated and try to maintain a nice even temperature. Too humid an environment can be a breeding ground for pests and diseases, so water well without over watering.

Here are some Organic pest control products that are safe to use on edible plants:
Bayer Organic Pest Control Spray
Garlic Wonder pest spray concentrate
Growing Success Organic Slug Killer

Avoid peat based composts or soil mixes as peat tends to encourage certain pests. Try some of our peat free composts here:

GroChar Seed Compost 8 Litre
GroChar Multipurpose Compost
Lady Muck Organic Manure
Bulk Bag Of Organic Compost

Contents

Growing in a polytunnel

Have you always been passionate about growing food? – all kinds of it and never liked buying food that can be grown in your own garden. Unfortunately in our climate in Scotland and many parts of the UK, there is a whole range of common vegetables that will do poorly outdoors and we need the extra heat and shelter of a greenhouse or polytunnel to get a good crop. Only in the most favourable areas could you grow tomatoes, peppers and cucumbers outdoors and even there the yield will only be a fraction of what can be achieved indoors. For example my favourite tomato variety ‘Sungold F1’ can produce about 500 most delicious cherry tomatoes per plant in a greenhouse or polytunnel. Outdoors you’d be lucky to get more than 50 tomatoes per plant.

Our growing season is also relatively short but with the help of an indoor space we can prolong the production period for most vegetables. You can harvest your first early potatoes in April, your carrots and beetroot in May and you can harvest salads all year round.

I promise you: getting a polytunnel or a greenhouse will revolutionise your gardening life. It will open up new avenues, you’ll experiment with new vegetables and you’ll be guaranteed a good food supply throughout the year.

You can also do some gardening work even if it rains outside. Even if we get a poor summer you can get the illusion that you are in a different country and enjoy the warmth at home.

Greenhouse or polytunnel?

The choice between a greenhouse and a polytunnel is quite simple. A greenhouse (also referred to as a glasshouse) is a lot more expensive but more attractive, your choice may naturally be a polytunnel as they have become very affordable in recent years.

Polytunnels come in all sizes and you can pick one that suits your garden. They are fairly easily assembled but it would be better to get some help and advice from somebody that has done it before. There is no right or wrong time of year to construct one up as our design allows you to jack the polytunnel up to tighten the cover, ”jacking the tunnel can be left until a sunny day”. You can sow or plant some vegetables nearly all year round.

Choosing a site for a polytunnel

Choosing the right place for your polytunnel or greenhouse is absolutely essential. It should be placed in full sun with reasonable shelter and good access from the house. Frost pockets should be avoided and make sure there is no competition from tree roots. Be aware that tree roots penetrate much further than the crown of the tree. We also advise to construct the polytunnel with one of the ends facing the prevailing wind, this cannot always be achieved so if that is the case then fit a set of crop bars which will give you 20% extra strength both snow and wind load. These are also handy to hang baskets or tie plants to.

Soil fertility in the Polytunnel

There is a simple rule: the healthier your soil is, the healthier your crops will be. In a polytunnel or greenhouse you can produce a lot more food compared to an outdoor plot. You can sometimes get four or five different vegetables into the same space in one year. That means you will need to feed it a lot more and the best feed for the soil is compost or composted manure. They enliven and improve the soil. Other organic fertilisers such as seaweed dust, organic poultry pellets or home-made liquid feeds can be used as supplementary feeds but never as a substitute to compost or manure.

Cladding a polytunnel

Cladding a polytunnel

A polytunnel cannot be covered or ‘clad’ on just any day. The weather has to be still – any wind will make the plastic sheet act like a parachute. In addition, the sun has to be shining – the warmth from the sun’s rays trapped in the polytunnel make the plastic more flexible and easier to handle and stretch. If there is no sun the plastic is prone to tearing.

If the weather is not right do not attempt to clad a polytunnel – even if a team of people have arrived to help or you have taken a day off work. Any attempt to clad a polytunnel in inappropriate weather will, at best, result, in a loose cover that will flap in the wind and may shorten the life of the plastic by years. At worst bad weather could result in a complete failure.

In the days before you intend to clad your tunnel there are certain things that must be done:

1. A ditch must be dug around the tunnel frame. 2. Hot spot tape must be stuck on the metal hoops so that the plastic sheet does not rest on metal in any place.
3. All rough edges or sharpe points must be covered with thick tape so that it will not catch on the plastic.

For details see the article “How to erect a polytunnel”.

To clad a polytunnel you need at least three people committed to working until the job is done. It always helps, though is not necessary, to have a few extra people when lifting the plastic sheet over the frame.

Lifting the plastic sheet over:

Photo 1. Before starting it really helps to make sure all the necessary tools and equipment are available. In particular, a knife is needed for cutting the plastic, spades for filling the ditch, and hammer, nails and wood for attaching the plastic to the doorframe.

Photo 2. The plastic sheet needs to be unrolled along one side of the polytunnel frame. Once unrolled the sheet will still be folded several times along its length. The different layers tend to stick together, so before lifting over the polytunnel frame the layers should be separated.

Photo 3. The sheet should then be pulled over the polytunnel frame. At least two people, preferably three or more, are needed for this job. The bigger the polytunnel the more people are needed. Holding both ends of the plastic sheet it should be gently lifted onto the frame and eased up.

Photo 4. The plastic sheet should never be forced, just gently manoeuvred to the apex of the frame. There may be times it seems impossible, but it will eventually get there. The only problem that might occur is if there is a gust of wind. The plastic sheet will act like a parachute. If it is too windy, give up. If there are occasional gusts of wind it might be exciting but it is not really a problem.

Photo 5. As soon as the sheet is over the polytunnel frame it should be weighted down with soil. This must be done quickly if there is any risk of there being more gusts of wind.

Photo 6. The plastic sheet must lie evenly over the frame, with equal amounts of spare plastic on each side and each end. Checking that the creases run parallel to the ground is a useful way of ensuring that the plastic is not skew. To temporarily secure the sheet to the frame the spare plastic at the ends can be tucked in through the doorframe. If the breeze is a little strong and the sheet is at risk of being blown a little soil can be put on the plastic in the ditches – but not too much as it will have to be moved.

It is worth taking a little break at this point to allow the air inside the tunnel to heat up. The warmer the plastic is, the more flexible it becomes, making the job of attaching the sheet to the frame much easier.

Attaching the plastic sheet to the polytunnel frame:

Photo 7. The plastic is first attached to the top of the doorframe at both ends. The plastic above one doorframe should be smoothed out, and a cut made diagonally, down and towards the centre from both corners, creating a flap of plastic that comes to a point 2–3 feet below the top of the doorframe.

Photo 8. The flap should be smoothed out, but not pulled. It should be folded inside and attached to the top of the doorframe on the inside of the polytunnel.

Photo 9.The door at the other end is attached in the same way, but before being attached the plastic sheet must be pulled as hard as possible. If the sun is shining the air inside the tunnel will quickly heat up, warming the plastic as well. It is worth letting this happen – take a break, have a cup of tea – as warm plastic stretches better.

Photo 10. If the plastic is warm it becomes supple and can be pulled extremely hard without any risk of damage. If the sun is not shining, particularly if the air temperature is cold as well, the plastic is brittle and will easily tear. Even if the plastic is warm, though, it must be held correctly for pulling. The best way is to bunch the plastic together and hold that. Clutching a single layer of the sheet when pulling is risky as fingers easily make a hole in the plastic.

Photo 11. The plastic can be attached to the doorframe by sandwiching it with wood strapping. Use several strips, and many nails.

Photo 12. Alternatively, in exposed sites where the polytunnel may experience strong gales in the winter, the plastic sheet can be attached to the wooden frame by cutting it into strips and rolling it around 1×2 inch pieces of wood, which are then nailed onto the frame. This method gives an extremely strong attachment and will not allow any slippage or tearing of the plastic.

Photo 13. After the plastic has been attached to the top of the doorframe at both ends, it must be buried in the ditch on the sides. This is done in a very particular order. Bury the plastic at the centre hoop on one side, do not pull the plastic down hard.

Photo 14. Then bury the plastic on the other side, at the exact opposite position. From then onwards, the plastic must be buried, hoop by hoop, first one side then the equivalent opposite side, moving gradually from the centre to the ends.

Photo 15. When burying the plastic the first time (see photo 13) it should be smoothed out but not pulled. From then on before the plastic is buried it should be stretched as hard as possible over the hoops. To do this put soil on the plastic sheet; lift the soil up by holding the loose plastic on the outside; and then stand on the soil (still holding the plastic). Your body weight will slide the bulky soil down into the bottom of the ditch, thus stretching the plastic. The warmer and sunnier the day the more pliable the plastic is, and the better the results.

Photo 16. Work from the centre to the ends of the polytunnel. To save time at this stage it is only necessary to wedge soil into the ditch where the hoops are situated. The ditch between the hoops can be filled in later. Only bury the plastic on the sides, the ends will be done later.

Photo 17. If the site is particularly vulnerable to strong winds, the plastic can be buried in the ditch even more securely by folding the spare plastic over, like an “S”, and adding more soil.

Photo 18. With the ditch done the next step is to attach the plastic to the sides of the doorframes. Starting at the top the plastic is pulled around the last hoop and the doorframe and nailed onto the frame on the inside of the tunnel. The job really needs two people, one to keep a tight pull on the plastic, while the other does the hammering.

Photo 19. The plastic must be pulled as hard as possible around the corner of the last hoop.

Photo 20. Towards the bottom of the doors there will be a lot of spare plastic to deal with. This is quite natural and just has to be folded out of the way. Folds must be introduced to accommodate it all.

Photo 21. The plastic at ground level at the ends can now be buried in the ditch. The soil should be tightly packed in, and the extra plastic sticking up form the ditch should be cut just at the soil surface.

Photo 22. When all the ditches are filled in and the doorframes done the tunnel sides should look neat, and there should be no loose plastic.

Making the door

There are as many designs for tunnel doors as there are tunnel owners. They can range from very sophisticated methods using hinges and proper door latches to just hanging a sheet of spare plastic from the doorframe. Generally, the simple methods are the easiest to maintain.

Photo 23. A simple but effective door is a sheet of plastic wrapped around a piece of wood and nailed onto the top of the doorframe. The plastic should be larger than the doorframe.

Photo 24. Two planks of wood sandwiching the plastic at the end and at a couple of places in the middle will give the plastic ‘door’ extra weight and strength.

Photo 25. The door is opened by rolling the plastic up and hooking some string around it.

Photo 26. In situations where strong gales can be a problem it is important that the door is able to prevent the wind entering the tunnel. In these cases a slightly stronger door is necessary. One method is to make a wooden frame that is slightly larger than the doorframe. This can then be covered with plastic and kept on with string crossed over the door.

Photo 27. A more sophisticated system involves hinges and doors that fit accurately within the doorframe. These systems are easy to manage day-to-day, but do require more maintenance over the years.

Preparing the inside of the polytunnel

Photo 28. Many polytunnel crops, such as tomatoes and cucumbers, need some sort of support when growing. It is much easier to put the supporting wire up before any crops are planted. The wire should be laid out along the length of the tunnel.

Photo 29. The wire should be attached to the end hoops with attachments slipped onto the end hoops when the polytunnel was erected.

Photo 30. With the wire firmly secured at both ends of the polytunnel, it should then be attached onto each internal hoop. A short piece of wire wrapped around the hoop and wire does the job nicely.

Photo 31. When the four lengths of wire are secured to each hoop they are unlikely to get in the way of anyone working in the polytunnel. The polytunnel is now ready for planting.

The finished job… and a few weeks later

For details about how to grow crops in a polytunnel click here.

© Joy Michaud

Buyers Guide

First things first, what is a polytunnel?

So some of you may be thinking, what exactly is a polytunnel and why would you need one in the first place?

A polytunnel is an elongated, polythene covered frame under which seedlings and plants can be grown. They provide protection to plants and can extend the growing season by several weeks. They come in various shapes and sizes with each polytunnel creating its own microclimate that can enable different types of plants to grow. This means that it’s possible to grow fruits and vegetables using a polytunnel that wouldn’t naturally grow in our climate.

Essentially, polytunnels can be used to protect your crops and plants from the destructive elements of the weather such as strong winds or hailstones. They allow any gardener to grow any type of plants, fruits, and vegetables in any region. They are able to grow that which wouldn’t normally be able to grow in their region’s climate.

The usage of polytunnels can be compared to glass greenhouses. These are also used for a similar purpose in regions with milder temperatures. But there are various differences between the two which we’ll touch upon in more detail later in the guide.

A polytunnel is not only known by that name, so you may have heard of it in the past being referred to as something else. It is also sometimes called a polyhouse, hoop greenhouse, high tunnel or hoophouse.

How do Polytunnels actually work?

The materials that are used to build polytunnels result in the interior of the tunnel heating up from solar rays. The hot air and humidity are contained in the building by the structure and the polythene covers, so it creates a microclimate for the plants to grow. You can control the temperature and humidity levels of a polytunnel by using either the equipment inside it or by manually adjusting the vents.

In the larger and more advanced polytunnels, there is enough space to allow harvesting machines inside to automate production. This is commonly the practice in commercial polytunnels. It has been done to cultivate production of soft fruits in the United Kingdom, such as strawberries, raspberries, and blackberries.

What is the price of a polytunnel?

The price for polytunnels can differ greatly depending on whether they are domestic or commercial polytunnels. This largely relates to the difference in size required for domestic and commercial purposes. Domestic polytunnels are what people growing plants or fruits in their home use in an effort to extend their gardening period over the colder months. Purchasing a domestic polytunnel means that you can protect your fruits, flowers, and vegetables from the British weather as and when needed. Commercial polytunnels are used by farmers and those who are producing food for commercial purposes, again for protection against the weather and to extend the growing period.

All the prices indicated below are inclusive of VAT on First Tunnels

Are cheap Polytunnels any good?

So, you might be wondering how much you really need to spend on a polytunnel. Would a cheaper one do the job just as well?

We’d recommend that you invest the required money into your polytunnel to get the best value for your money. Ensure that you purchase it from a credible polytunnel manufacturer rather than trying to save money and potentially investing in a substandard structure. It doesn’t necessarily need to be the most expensive option, but the materials used need to be strong and durable enough to offer your plants the necessary protection.

If you don’t invest in a high-quality polytunnel, you may find yourself losing more money in the long term if you are unable to protect your crops. This is especially true for when a polytunnel is being used to grow plants, fruits, and vegetables on a larger scale for commercial purposes.

When you are planning what you will spend on your polytunnel, you also need to budget for any accessories or spare parts that you may need. The extras can often add up over time so it often makes sense to buy what you know you’ll need upfront.

Which is best, polytunnel or greenhouse?

If you’re wondering what the difference is between polytunnel and greenhouses, we can understand the confusion. On the surface, it can be hard to decide which option is the best for you. Both come in a range of shapes and sizes. They also ultimately serve the same purpose by creating optimum growing conditions for your plants. However, there are some fundamental differences which should make it an easy choice:

  • The biggest difference between greenhouses and polytunnels is the cost. Compared to greenhouses, polytunnel offer really good value. This is especially true if you’re looking for something larger in size, as you get more growth space for your money. The exact same strength of material and ventilation will be provided for a lower price. Also, durability is not an issue as once you’ve erected them they will likely stand for many years.
  • It is easier to customise polytunnels than glass greenhouses. Once greenhouses are fixed, they can be difficult and expensive to modify.
  • Polytunnels can be more difficult to repair, though it is possible. On the other hand, if you break a pane of glass in a greenhouse, it is fairly easy to replace.
  • Preparing a base for a glass greenhouse can take more time, as they require a completely flat base. Polytunnels don’t have the same requirements, so the preparation time before installation is shorter.
  • It can take time for your glass greenhouse to be manufactured, especially if it is a custom piece. Polytunnels are manufactured and delivered much more quickly
  • Polytunnels are not permanent structures and can be transported to different areas or removed as and when needed. Glass greenhouses can’t be moved and would need to be rebuilt in another location if that was required.

It all comes down to affordability. If you are looking for a more cost-effective structure to grow your plants that can be easily customised and moved around, then polytunnels are for you. Ultimately, both achieve the same growing benefits for your plants.

How should you choose a polytunnel?

There are a few key elements to consider when looking for a polytunnel, and we’ve listed the most important ones below:

  • Consider your own requirements and the space you have available. It is important to ensure that you’re not investing in a polytunnel that wouldn’t be the right fit for your own plot or garden. Most polytunnel manufacturers have a wide range of sizes available so you should easily be able to find one that suits your needs.
  • When do you need them by and can you construct them yourself? Most polytunnels are simple and quick to construct which is what attracts many people to them. Ensure that yours will be delivered on time and with detailed instructions by placing an order at First Tunnels.
  • Are the materials durable and high quality? You want a guarantee on the lifespan of the polythene covers of your polytunnel. This will help ensure that you’re not having to invest in regular replacements. At First Tunnels, we offer a 5 year guarantee for our polythene covers.
  • Planning before you purchase is important to make the right assumption on what size you will need. You need to make a plan of what you will grow and where to make sure that you’re buying a polytunnel that will have enough space for your needs.

It is also important to mention here that you should look into whether you may need planning permission before you install a polytunnel. You don’t usually need this, but you may if your site is near a listed building or area of conservation.

How should a polytunnel be cleaned?

In the winter months, you may find that the dampness in the air has led to your polytunnel cover becoming coated with green algae. It’s extremely important that you get this cleaned immediately, as it will obstruct the light and hinder the growth of your crops. Even if you see the algae on just one side, it is recommended that you clean everywhere regularly to ensure you’re getting the optimum level of light in your polytunnel.

So, how do you get started with the actual cleaning? Start with enlisting the help of a friend and then follow the steps below:

  • Find a form of sheeting (such as a fabric), two lengths of rope, and a cleaning fluid. Pick a cleaning fluid that is made to remove algae. You’ll also need two tennis balls, a sponge, a hose, a bucket of soapy water, and a bottle that you can spray the cleaning fluid with.
  • Once you’ve got all the equipment together, insert the tennis ball on both ends of the sheet and tie it up with the rope. This makes the sheet weighted for you to use for cleaning. The weighted sheet then needs to be dipped into the soapy water in the bucket.
  • Start off by cleaning the top. Using the hose, spray water all over the top of your polytunnel. When you’ve managed to wet this, toss your weighted sheet over it.
  • Ask your helpful friend to go to the other side of the tunnel and take hold of the weighted sheet from the other side. Then both of you need to start pulling the sheet from side to side, which will work in rubbing off the algae and any other dirt from the top of the tunnel. Work your way down each section and repeat as often as needed.
  • Once you’re satisfied, spray water all over again using the hose. This will help ensure that any leftover dirt or debris is sprayed away.
  • For the sides, the cleaning process is similar to washing a car. Wet your sponge and spray the cleaning fluid onto it. Using this sponge (or a soft brush if you prefer) proceed to wipe the sides of the polytunnel clean. Any leftover dirt should be rinsed off using the hose.
  • To deal with any algae and dirt on the inside of the tunnel, use a sponge again. Spray the cleaning fluid onto it again and work your way around the interior of your polytunnel. It is also recommended that you use a non-toxic cleaning product to ensure that your plants don’t suffer from any toxins.

If you follow these cleaning steps as and when you see any algae build up, you’ll be allowing in the maximum level of sunlight and giving your plants what they need to grow.

How can you secure a polytunnel?

Your polytunnel needs to be firmly secured to the ground, especially if you’re setting it up on a slope. To ensure that you’re going to be able to secure it effectively, purchase your polytunnel from a reputable manufacturer that provides detailed instructions and after-sales care if needed. Many polytunnel manufacturers even offer a construction service if you need it.

It is not difficult to construct a polytunnel, but it’s also not a task that you should take lightly. You need to secure your structure so that it will endure any weather conditions and last the test of time. Some people may compare it to putting up a tent, but it definitely needs to be more firmly secured than that.

In terms of how long it will take, this can vary depending upon specific factors such as the weather conditions and the size and features of your polytunnels. It also depends on how good you are at doing DIY projects! We’d recommend enlisting the help of a friend to get it completed quicker.

Polytunnel repair – what you need to know

Polytunnels are generally very sturdy and durable, but like any product, they are prone to damage and will sometimes need repair. We have all the information you need on what to do in case of any damage, and how to help prevent this in the first place.

Firstly, you need to ensure that you’re getting the right cover for your polytunnel in terms of thickness. The cover for your polytunnel should be a minimum of 720 gauge (about 180 microns). This is the level of thickness which is guaranteed to last about five years. It can even last up to ten years in some cases.
As with most products that are used outdoors, you need to monitor it closely and regularly to keep a close eye on any potential issues. The area that is most likely to suffer damage is the polythene cover so this should be checked on a regular basis. Any small tears or damage that you spot need to be dealt with as soon as possible to prevent the issue worsening.

If you spot a tear, then you should repair this immediately using polythene repair tape. The reason to use this instead of regular tape is that it is transparent and UV stabilised. It will avoid the obstruction of sunlight without being damaged by the sun rays itself. Consider taping both sides of the tear to result in a sturdy and strong finish.

Other than the polythene covers, make sure you check regularly for any damage in the frames or the hoops of the polytunnels. Deal with any damage as and when you spot it as soon as possible. Remember, if you leave it too long before you mend it, there is a danger that the damage could grow. Also, try and deal with the cause of the damage so it doesn’t happen again.

To prevent damage along the hoops, anti hot-spot tape should be used when constructing the polytunnel. This works to effectively separate the hoop from the polythene cover and prevent heat degradation. With frequent inspections and quick repairs, your polytunnel will last you years. Just make sure you give it the care that it needs!

Hopefully, this guide has helped answer many questions about polytunnels, their benefits, and the essentials of caring for one. If you’re considering purchasing a polytunnel.

How to Buy, Site and Erect a Polytunnel

Details on covering can be found on manufacturers’ websites (see references). If in doubt stick to the basic polythene cover. Use hotspot tape to protect the cover where it touches the structure or its lifetime will be greatly reduced.

Access doors are one of those things that we all forget about until it’s too late. Make sure that you have enough and that you can get to them easily in any kind of weather. Check that the doors are big enough to get a wheelbarrow through! Some of the doors advertised by manufacturers are way too small – if your polytunnel is wide enough consider at least one set of double doors.

Ventilation

One of the things to think about very early in your polytunnel choice is ventilation. Even with good ventilation the summer temperatures can reach in excess of 38ºC (100ºF). I am sure many of you saw the TV small-holder, Hugh Fearnley-Whittingstall, using his polytunnel as a sauna. I must admit to having felt like I was in a sauna from time to time, although unlike Hugh I keep my clothes on to avoid scaring the neighbours.

The most common way to ventilate is through the doors at the ends. The area for ventilation however is often inadequate. On more than one occasion I have had to spray water on the inside to reduce the temperature or provide additional shade. In future I would go for a tunnel where the sides can be raised in the summer. Typically, the ventilation holes are covered with some sort of insect screening. I have, however, resorted to leaving the doors open in midsummer and letting the insects in with no apparent harm.

During the winter the polytunnel will provide little protection from frosts. The insulating characteristics can be improved by wrapping the structure in bubble wrap. This is not only expensive but tedious and can be avoided by either growing only those crops that don’t care about the temperature or by using a divided polytunnel. I have about of the tunnel divided off from the rest. This enables me to have a warm section of polytunnel in the winter for frost sensitive plants. The insulation area is much smaller and the heating requirement is reduced.

A divided polytunnel also allows me to grow plants that like different conditions in each part. I can ventilate and water differently affecting the humidity and temperature in each section. For example, aubergines like warmer conditions than tomatoes whilst both prefer less humid conditions than cucumbers.

Finally, get the biggest one you can afford or fit in – you will never have enough space!

Location

Your polytunnel should be an integral part of your permaculture system. In terms of zones*, the tunnel fits firmly into Zone 1 due to the frequency of visits required and the complexity of the work.

Key factors in placing the polytunnel within Zone 1 are sun, temperature and wind. Wind is the easiest to deal with. If you build your polytunnel correctly it will not be structurally affected by the wind, with the exception of tornados. It is however practical to have it somewhere sheltered from the wind, thus reducing heat loss and in turn increasing yields. In Cambridgeshire where I live, we are open to the cold east winds so I situated the polytunnel on a sheltered side of the garden. Clearly the use of windbreaks in the wider context of the whole plot is the best solution.

More important is to get the maximum sunlight to the polytunnel. Placing the long axis east-west is optimum. However, this does lead to a dilemma in the middle of summer when you really could do with some shading due to high temperatures. What I have done is place the polytunnel so that in summer a nearby tree provides some shade around noon time and prevents scorching. During the rest of the day the shadow doesn’t cover the tunnel and the amount of sunlight is maximised. As the tree is a silver birch, in the winter – when you need all the sunlight you can get – it doesn’t shade the tunnel at all. If you don’t have such an arrangement you will have to be very careful about keeping temperatures down in summer and providing shading by other means – either artificial or natural. Place the tunnel to avoid frost hollows!

Do not forget access when locating your polytunnel. Not only will you need access to the doors but you will need to clean the polytunnel from time to time and thus access around the tunnel is helpful. Also covers will have to be replaced sometime in the future. Plan the services you might need in the polytunnel, is it close to a water supply and do you need electricity for heating or lighting?

Assembly

Assembling your polytunnel is rather like assembling flat-pack furniture – it should be easy but can be frustrating. I would ask your proposed supplier to send you a copy of the instructions before ordering to check they are easy to use – look for ones that show real pictures of assembly and are not all text. Check the parts you receive matches the parts list – it took me ages to realise that a piece was missing and I spent a whole afternoon trying to figure out how to assemble one part of the structure.

You will need help! Two people are about the minimum for the structure and a third could be useful for the cover. Do not try and put the cover on when there is any wind or you will either rip the cover or else end up with it sailing down the road. A hot day is good as the heat will soften the material, allowing a tighter fit. This will increase both the strength of the structure and the life span of the cover. Remember to put the cover on the right side up (yes, there is an outside and an inside to many types of cover) – having to remove a cover and replace it cannot be much fun.

Caring for your Polytunnel

Cleaning is best done once a year. I use a biodegradable washing up liquid and a long handled mop and hose. Repairing holes in the tunnel can be done with repair kits available from the manufacturer although personally I would not bother for small holes and if necessary use any tape you have handy.

Polytunnel Gardening

Watering is absolutely essential, especially in the summer where you may need to water daily. I use a series of soaker hoses pegged to the ground. These not only get the water to the right place but helps avoid Phytophthora fungus, which can cause major problems. Increased ventilation helps combat this.
Another problem in polytunnels is maintaining soil fertility from year to year. It’s essential to add organic matter to the soil – I use well-composted chicken manure mixed with garden waste compost and/or leaf mould. In addition, I use a crop rotation system.

In such a limited space it can be difficult to do a proper rotation without leaving areas of the tunnel unproductive. My rotation system is based around the major summer crop, which in my case is tomato. About half of the main part of the tunnel in the summer are tomatoes with the rest given over to various types of peppers. In the small section I grow more difficult crops like okra and aubergines. Main crops are interplanted with lettuce and herbs such as basil.

The winter part of the rotation is based around crops that mature early in summer before I put the tomatoes in the ground (which are raised initially in seed trays, then pots). As I want to build fertility, I use broad beans and winter hardy peas – these I get to mature in about May by planting before winter. The remainder of the polytunnel in winter is taken up by crops like endive, winter radish, and other hardy greens such as lamb’s lettuce. These are cropped through the winter to provide fresh greens. All the winter crops are then removed for the summer crops. I also use the polytunnel for early crops of onions and garlic. However, garlic needs a frost to produce multiple bulbs so don’t grow these in a heated area. Planting is also organised so that I do not grow any crop in the same part of the polytunnel two years running.

One final factor to remember in choosing the crops is pollination. If you are growing self-pollinating crops then you need not worry. If you keep the polytunnel closed or ventilated with mesh screens then you can have pollination problems. What I normally do is treat the polytunnel as I would any other part of the permaculture environment and encourage insect life into the tunnel. In the main growing season I leave the doors open during the day (required to reduce the temperature) which means I get most insects in (even butterflies), plus blackbirds who delight in turning the place into a mess! In return I get good pollination and have so far had virtually no pests. Those that I have had, usually greenfly, I have cured using a soft soap spray.

Crop Production

As an example of how productive my 4.25m (14ft) polytunnel can be, I can give rough figures for winter 2002 to summer 2003. During the winter season we grew around 25 endive, 10-15 large bulbs of garlic, early peas (probably around 2.2kg/5lbs picked as mangetout) and broad beans (around 4.5kg/10lbs or so). In the summer we had in excess of 54kg (120lbs) of tomatoes, around 50 green peppers and a little okra. Of course, last summer was exceptional, but I didn’t get any summer use out of the small end of the tunnel as it was used for storing some exotics.

So in conclusion I believe a polytunnel is an essential part of the permaculture garden – I hope you do too. Have fun!

Useful Resources

Mark Smith and his wife Anne run @one Associates which offers a holistic approach to helping people gain a deeper understanding of themselves and their environment.If you have any questions feel free to contact Mark at: [email protected]

How To Grow Food in Your Polytunnel All Year Round

First Tunnels supplied my polytunnel and provided excellent service and good assembly instructions. Clovis Lande are suppliers of polytunnels – their website has a lot of detailed information on polytunnel covers.

*For a good description of Zones see:
The Earth Care Manual by Patrick Whitefield on the Green shopping website.

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Building a Polytunnel

What is a Polytunnel?

Propagating your own seedlings from seeds and growing small plants at any time of year is very easy with this basic inexpensive polytunnel that you can build yourself in a short time from readily obtained materials.

How does a Polytunnel work?

A polytunnel can be a lightweight greenhouse of small to large (eg commercial) dimensions. If constructed with a bit of care it can be quite weather resistant, versatile and practical. It is a great way to begin to learn a fundamental gardening technique – producing your own plant seedlings cheaply.

It is a useful aid in extending the growing season, beginning in winter, in Canberra’s “cool climate”. There are many ways to construct a polytunnel. The outline presented here is for a small polytunnel suited to the Canberra region, or equivalent.

Construction phase

Firstly, chose a suitable spot which receives at least 6 to 8 hours direct sunlight per day. It should be reasonably flat, whilst avoiding pooling of water. Orientate the polytunnel so that one side is facing north.

Mark out the area where you wish to build the polytunnel eg at least 1.5m wide and 2 to 3m long. Cut some metal curtain rods or wooden dowelling rods into sections (stakes) about 20cm long – these need to fit into lengths of poly pipe or tubing (19mm diameter preferred) to form the frame of the polytunnel. The wooden dowelling stakes should be sharpened to a point or cut at an angle to enable easier driving into the ground.

Drive the metal or wooden stakes in pairs into the ground about 1m apart. Push the poly pipe onto these stakes. The poly pipe needs to be long enough (eg 2m) to form a semicircular hoop. These hoops can be cut from a longer length of poly pipe or made from shorter lengths joined with compatible joiners.

Once the hoops are in place, about 1m apart, place garden stakes (or equivalent), about 1.5m from each end of the proposed polytunnel. Run a rope to form a “backbone” between the end stakes, attaching them to the hoops on the way – this adds some rigidity to the structure.

Place builders film (or shade cloth if using the polytunnel in warmer weather) over the hoops, with enough material at each end to reach the ground near the end stakes, and wide enough to cover the structure with sufficient excess to allow bricks or stones to be installed along the sides to secure the film.

The film can be lifted at either end to allow passage of air to avoid overheating on sunny days and lifted along the sides to allow access. The film should be put back in place overnight. Secure the film to the hoops with ready-made clips or DIY clips made from short lengths of poly pipe, split along their length.

The seed germination trays should be off the ground inside the polytunnel, eg sitting on bricks or inverted small pots. Fill the trays with potting mix and sow some seeds as appropriate into them.

Your polytunnel is ready to produce seedlings. Remember to open at least one end on sunny days and to water/add fertiliser as appropriate.

What you’ll need

Materials:

  • Builders’ film (roll) – various lengths available; shade cloth for warmer weather
  • 19mm irrigation poly pipe – cut to length or join with joiners if shorter lengths (eg 1m)
  • Stakes eg short sections of curtain rods or wooden dowelling rods
  • Camping pegs/garden pegs for the ends
  • Rope
  • Bricks or stones
  • Seedling trays (at least four to start)

Tools:

  • Tin snips or large scissors
  • Mallet or hammer

Greenhouse vs. Polytunnel – Which one is better?

The benefits of rainwater collection

Water collection is yet another important factor to consider as rainwater harvesting has many benefits. It is an eco-friendly process, a money saver and a nutrients supplier. Greenhouses are easier to adapt than polytunnels, with regards to fitting them with an effective rainwater harvest system.

A good solution to the water collection problem in polytunnels is using a gutter system. You can install a rainwater gutter to one of the sides of your polytunnel, leading straight into a water tank. This way, you’ll have a sufficient quantity of irrigation water that you can use whenever you need to.

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What can you grow in a polytunnel and a greenhouse?

What to grow in a polytunnel

Fruits:

  • Strawberries – Mix in some compost with the soil before you plant them.
  • Raspberries – Add mulch to the soil to keep it moisturised.
  • Melons – They like humid conditions and fertilised soil.

Vegetables:

  • Tomatoes – Boost the soil by adding organic matter to it before planting.
  • Cucumbers – Create vertical structure in order to allow the crops to grow in a polytunne.
  • Artichokes – They thrive well thanks to the warmth and humidity that polytunnels create.

Herbs:

  • Rosemary – It grows well in warm conditions and does not need frequent watering.
  • Oregano – It helps soil moisture retention.
  • Basil, Thyme, Chives – They repel various pests and protect the crops around them.

Trees:

  • Peach – Polytunnels protect them from frost and birds that like their fruits.
  • Apricot – They need some extra heating.
  • Citrus (Lemon, Orange, Lime, Grapefruit) – Polytunnels retain the ideal temperature for them to thrive in the winter months.

Flowers:

  • Tulips, Sweet Peas, Foxgloves, Lupins – They attract bees, pollinators and other beneficial insects.

What to grow in a greenhouse?

Flowers:

  • Roses – They need enough moisture and around 6 hours of direct sunlight per day.
  • Tulips – These plants need protection against pests and frost, so this is the perfect environment for them.
  • Orchids – Provide them with the right temperature. Avoid over-watering them.
  • Lupin – Constant sunlight and moisturised soil is what they need. Lupins can grow in most soils, even those that are poor in nutrients, except in chalky soil.

Vegetables:

  • French Beans – A sunny spot and moisture is all they need.
  • Aubergines – Warm the soil a couple of weeks before planting to protect them against frost.
  • Peppers – Water and fertilise them regularly. Place peppers in a sheltered, sunny spot.

Fruits:

  • Grapes – Water them frequently during the growing period.
  • Kiwi Fruits – They should be grown in sheltered sunny spots.

Crop options are limitless. Both types of facilities create appropriate conditions for crop growing. Polytunnels are usually used for growing large amounts of fruits and vegetables. On the other hand, greenhouses are better-looking structures. They are often used for growing various classic or exotic flowers or even tropical fruit.

Advantages and Disadvantages of Polytunnels

Advantages of Polytunnels

  • Polytunnels are a budget-friendly option.
  • They can offer more growing space.
  • Polytunnels are more flexible structures.
  • They can be modified to incorporate various additional features or to achieve a specific purpose, such as widening the doors or expanding the plant beds.
  • There is a possibility to increase the interior space.

Disadvantages of Polytunnels

  • They can be blown away by strong winds, which is why the frame should be attached to the ground properly.
  • Polytunnels are prone to damage, caused by pets and birds.
  • If the sheeting is not straight and tightened properly, condensation can build up and harm the plants, as high humidity levels promote mould growth.
  • Covers need to be replaced every 5 years.
  • They are harder to fit with a rainwater collection system.

Pros and Cons of Greenhouses

Pros of a Greenhouse

  • Greenhouses are more visually appealing constructions.
  • They are mainly used for growing flowers but you can grow crops in them as well.
  • Most frames are made from powder coated aluminium, which protects them from oxidising.
  • They protect plants better against pests.
  • If you use toughened glass, they can withstand bad weather conditions, too.

Cons of a Greenhouse

  • Site preparation requires a lot of effort. The base must be firm and flat.
  • It can take up to several months to get your custom-made greenhouse delivered to you. Unless you want to buy a standard-size one.
  • Greenhouses are more complex structures. It takes professionals a couple of days to install one.
  • They are expensive and difficult to move as well.
  • If damaged, you’re likely to be looking at replacing several glass panels.
  • Since most people prefer to position their greenhouse next to the house, there isn’t always enough space to install it.
  • Apart from the construction itself, supplying kits and electric heaters are not cheap, either, and this is just another one of the disadvantages of greenhouses.

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Did you know…?

Did you know why are greenhouses called ‘green’?

Greenhouses are eco-friendly structures which reduce energy bills. They are also good for the environment. They improve the air around your house. People often ask ‘Why are greenhouses called green when they are invariably clear glass or plastic?’.

According to some studies, greenhouses are called this way because they used to be treated with a green dye. It absorbed light and produced heat. In fact, people still use it today in salt production. It increases the absorption of UV lights by the sea in order to speed up evaporation.

Greenhouse sheeting is usually made from translucent materials – clear plastic or glass. This allows sunlight to come in and stimulate the photosynthesis process. It combines carbon dioxide and sunlight’s energy which feed the plants. Around 6 hours of daily sunlight exposure is what plants need thoroughly.

Do I need planning permission for a polytunnel?

Polytunnels that are used for domestic purposes are known as ‘permitted developments’. Commercial polytunnels are not considered as such.

There are regulations that should be followed. The structure should be within a certain height, position, size, movability, etc. A local planning authority can decide if you need planning permission for a polytunnel or a greenhouse. You can find some additional information on Planning Portal.

Don’t hesitate to contact your local council office to get some more information in details. Or, you can always find your answers online.

Before you make a decision, take your time to plan and define your needs. Both structures come in various shapes and sizes. Greenhouses are appropriate for you if you want something extra appealing for your garden. They create optimal environment for various exotic plants.

On the other hand, polytunnels are something you might not want to place next to your house but in the backyard instead. Being easily expandable makes them appropriate for growing large quantities of edible plants and start up various flowers from seeds. They are more flexible and are the less expensive option, too.

Did you find this article helpful and worth sharing? Or do you have any other interesting ideas on what you can grow in a polytunnel? Let us know in the comments below!

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Greenhouse or Polytunnel. Which is best? The facts!

Greenhouse V Polytunnel Cost

Greenhouse with Toughened Glass

2.4m x 3m (8ft x 10ft) from £690. 3m x 3.6m (10ft x 12ft) from £1200. 3.6m x 5.4m (12ft x 18ft) from £3000

A Polytunnel with Thermal Anti Fog polythene, anchor plates & base rails

2.4m x 3m (8ft x10ft) from £379. 3m x 3.6m (10ft x 12ft) from £437. 3.6m x 6m (12ft x 20ft) from £588

Cost per sq ft Growing Space

Greenhouse

2.4m x 3m (8ft x 10ft) = £8.63 per sq ft. 3m 3.6m (10ft x 12ft) – £10 per sq ft. 3.6m x 5.4m (12ft x 18ft) = £13.89 per sq ft

Polytunnel

2.4m x 3m (8ft x 10ft) = £4.74 per sq ft. 3m 3.6m (10ft x 12ft) – £3.64 per sq ft. 3.6m x 5.4m (12ft x 18ft) = £2.45 per sq ft

Site Preparation

Greenhouse

Must be put up on a firm, level site.

Polytunnel

A slight slope can be accommodated and even helpful in heavy soils. Slopes can be dealt with using extended foundation tubes.

Construction Ease/Time

Greenhouse

60% of people buying a greenhouse opt to have them installed. On average, a 2.4m x 3m (8ft x 10ft) may take a weekend to construct, or one day for an experienced fitter.

Polytunnel

95% of people buying a Polytunnel opt to erect it themselves. On average, a 2.4m x 3m (8ft x 10ft) polytunnel will take a couple of days to construct. Half a day for an experienced fitter.http://www.firsttunnels.co.uk/faqs.asp

Cover/Glass Option

Greenhouse

Horticultural glass, toughened glass or polycarbonate. Toughened glass is much safer as if it breaks it falls into blunt cubes. Approximately 20% more expensive than normal glass. Polycarbonate offers best insulation but has a limited lifespan and is prone to blowing out of the fame.

Polytunnel

Standard Polythene, Thermal Anti-Fog or White Polythene. First is the cheapest and the last is primarily for plants which prefer reduced light. Thermal Anti-Fog is designed to reduced running condensation which can damage plants and improve heat retention.

Greenhouse

Cheaper greenhouses tend to offer limited ventilation, usually just through the roof openings. This offering lower level side ventilation will maximise air changes.

Polytunnel

For up to 3.6m (12ft) long tunnels, a door at either end will provide adequate ventilation. (A sliding door also gives you greater control over ventilation) For longer polytunnels, net side ventilation can be added at one or even both sides.

Cons At A Glance

Greenhouse

Site MUST be level. Get less growing space for your money. More expensive. Too much direct sunlight can cause problems.

Polytunnel

Water collection can be trickier. Prone to damage. Ventilation less refined.

Pros At A Glance

Greenhouse

Looks good. Long life. Water collection easy. Automatic ventilation possible.

Polytunnel

Cheaper. The bigger you go the cheaper it gets. Suitable even for sloping sites. Straight forward to construct.

Conclusion

For many gardeners, a greenhouse is not just somewhere to grow your plants – it is a status symbol! So if appearance was a consideration a Greenhouse would be Top. However, where practical growing space is required, getting much more growing space for your money and the fact a polytunnel is easier to construct – A polytunnel is likey to be the preferred purchase! “Well done to the Polytunnel”

Polytunnels vs. Glasshouses

For those taking the next step and investing in a greenhouse, it can be sometimes hard to find which option suits best. My advice is to find a greenhouse that compliments your garden while also being practical for its intended use.

Firstly you should avoid generalising about characteristics of Polytunnels vs Glasshouses (e.g. thinking Polytunnels are stronger than Glasshouses or Vice Versa). There are a huge range of Polytunnels from extremely strong to extremely flimsy and the same applies to Glasshouses. One generalisation one can usually make is that something very cheap is probably very flimsy, and usually to have something strong is going to cost more that something weak.

Sometimes customers ask which is better for growing plants – a Polytunnel or a Glasshouse, but if adequate ventilation is provided (and that depends on the features or model you choose) then the growing conditions are much the same.

Ultimately this debate boils down to personal choice, so instead of given my opinion on which I think is best I have listed below some pros and cons of both Polytunnels and Glasshouses. I hope this makes your search that bit easier…..

Polytunnel Pros

If you are looking for something quite large, the difference in cost between a Polytunnel and a Glasshouse is quite substantial. Vegetables particularly take up a lot of space, so a Polytunnel will give you a larger area of protected space to grow for your money than a Glasshouse – all things in terms of strength and ventilation being equal.

There is more flexibility to customize your structure to suit unusual needs. i.e. widening the doors for machinery or coping with sloping ground, a Polytunnel is much more easily modified than a Glasshouse.

Straight sided tunnels provide a very pleasant working area internally as a result of the height. If your 6’ 2” like me, this is an added plus. It also means taller crops are less likely to be touching off the polythene cover.

Polytunnel Cons

Although Polytunnel Covers are UV stabilised to give long life, they do need to be replaced periodically (depending on the grade chosen usually every 4 or 5 years, but some customers getting much longer – it depends on many factors such as how much sunlight the cover get. With larger structures this can be a bit of a headache, it requires the customer to think ahead and test the polythene when coming up to its expected end of life so to anticipate when to recover it rather than having the cover fail in the middle of a period of inclement weather.

Polytunnels can prove slightly harder to construct as it involves holding a large sheet of polythene, so any wind at all makes covering tricky. Tensioning the polythene to the adequate tension is a developed skill. It is very achievable by all but takes patience and planning when covering ones tunnel for the first time

In a glasshouse if you break a pane of glass you can replace that pane. Do the same with Polytunnels cover and you have to try and tape it (not the best or most permanent job). In the worse case situation you might even have to recover the full tunnel if needs be.

Prone to attack by cats and dogs (and birds pecking at insects at the ridge). Not the most common of problems however I have heard of it occurring on more than a few occasions. Therefore worth noting if you have pets around.

Polytunnels are not an item of beauty to most, so generally people want to keep them out of sight in the vegetable plot.

At present there are not as many options for ventilation in Hobby Polytunnels as there are for Glasshouses. Ventilation is usually only supplied by opening doors at both ends whereas a Glasshouse can have roof vents, louvre vents and these can easily be fitted with automatic opening devices which do not need electricity to work.

Glasshouse Pros

Glasshouses are available in very attractive designs that compliment a garden, such as Orangeries, Victorian style Models and Dwarf Wall Greenhouses, with the frames being available in a range of colours. They do not need to be kept out of sight so can be situated nearer your house and this can be an advantage in terms of making use of it.

Glasshouses will need periodic cleaning as do Polytunnels but you don’t need to replace the covers every few years.

Aluminum has a very long lifespan and powder coated models protect the aluminium from oxidising and so retain the good looks of the Greenhouse for longer.

Glasshouses are available with a wider range of ventilation options than Polytunnels and also there is an abundance of shelving and other accessories for them that are not widely available for Polytunnels. For example rainwater collection from a Glasshouse is simple as they nearly all have built in gutters, it is just a question of ordering downpipes and a water barrel for it.

Glasshouse Cons

A flat and level base is required for a Glasshouse, so generally speaking the preparation of the site is a bigger job than a Polytunnel.

The lead time for supplying some Glasshouses can be up to 3 months, so you need to plan ahead (unless it’s a standard model, these are normally in stock by glasshouse suppliers). Most Polytunnels that are produced in Ireland can be manufactured within days of order.

To summarise

Joking apart, many customers get both a Polytunnel and a Glasshouse. The Polytunnel is at home in the vegetable patch out of sight, doing a fantastic job of protecting the vegetables from excess rain and wind, providing excellent growing conditions, the Glasshouse up near the house, a feature in the garden and used for propagation, flowers, bedding plants and perhaps a few tomatoes. So the question does not have to be Polytunnel or Glasshouse, it can be which Polytunnel and which Glasshouse (probably not all at once).

Guides

First Tunnels’ Polytunnel Experts Are The Pick Of The Crop

Part of the fun of owning a polytunnel is picking the brains of people who really know how to make the most of the real growing potential. So we’re making it easy for you…with some of the best brains in the business!

This site now includes features, produced exclusively for First Tunnels by Andy McKee and Mark Gatter – the best-selling authors of ‘How to grow food in your Polytunnel’ and ‘The Polytunnel Handbook’. Plus…Paul Peacock, presenter, from BBC’s Gardeners’ Question Time.

Check out their hints, tips, ideas, do’s and don’ts and general expert know-how on making the most of every inch of your polytunnel…every day of the year!

Growing Guides

by Mark Gatter

The Growing Guide will take you through a whole 12 months of activity in your polytunnel. What you should be doing, what to look out for, maintenance and ideas to maximise your crops, PLUS… what to plant, pick and enjoy! View our Growing Guides.

Top Of The Crops

by Andy McKee

Top of the Crops is the definitive guide to achieve crop success. Whether you’re an old hand looking to try something new, or a complete novice growing for the first time Top of the Crops will give you the confidence to achieve crop success. View our Top Of The Crops.

Tunnel Vision

with Paul Peacock

We know many people build their polytunnels at the weekend or over a bank holiday when our office is closed, so we have produced a series of ‘handy-cam’ polytunnel construction videos. View our Videos.

Andy, Mark and Paul are also actively involved with our Facebook pages on a daily basis. Either posting pictures, sharing hints and tips, or answering other gardeners questions. If you have a question, or want to share some of your polytunnel gardening experiences, join our group on Facebook where you’ll find hundreds of other like minded people making the most of their polytunnels.

How to extend your growing season with a polytunnel

In autumn, winter salads, overwintering brassicas and oriental greens are ideal, while in winter you can enjoy cut-and-come leaves, spinach and chard and sow your onions.

Peaches and nectarines can be brought inside to avoid peach leaf curl.

Important considerations

Do check with your planners to see if you need permission. Be neighbourly and take into account that next door doesn’t want to gaze at it either!

Low tunnels make screening easier, and they can go on sloping ground, although it is easier if the slope runs along the length, rather than the width.

The hoops should be vertical and not perpendicular with the slope. Usually there is little option as to where to site a tunnel and the orientation.

Ideally, avoid an exposed, windy site and choose a sunny spot. Nearby trees will cast shade and roots will seek the rich, moist soil in the tunnel.

East-west orientation gives maximum sun throughout the day, but if you have to site it north-south there are advantages: the sun will beat down on the narrow end giving rise to lower daytime temperatures in the centre, which can limit pest build-up.

An average-sized tunnel for most of us would be 3m x 4.5m and it would be about 2m high at the ridge.

The proportions can vary, though longer than 10m requires ventilation in the centre – this is where pests and disease usually start.

A disadvantage with polythene tunnels is lack of air movement – you can get searingly high summer temperatures and high humidity levels in winter.

So make sure you have doors at either end with built-in ventilation panels made of rigid plastic windbreak netting or similar.

Types of Tunnel and Covers

Joyce Russell’s new book, The Polytunnel Book gives good advice and inspiration. A basic 3m x 3m tunnel complete will cost £264.60 (with assembly, £464.60 from First Tunnels, 01282 601253). Options include permanently fixed hoops with concrete or movable ones pushed into tubes in the soil.

The polythene can be fitted to a base rail or buried, the former makes replacement of the cover (which costs about £100 and needs to be done every four to 10 years if it’s 500-600 gauge and UV-treated) far easier.

There are many other sorts of tunnels, including geodesic dome shapes, greenhouse styles (Haygrove) or ones with higher vertical sides.

There are also different types of polythene cover, such as bubble polythene for extra warmth and exposed sites and Thermal Anti-Drip (Premier Polytunnels).

Under ordinary polythene, large droplets form and drip. It can be the kiss of death to plants as it encourages fungal disease.

Some films have additives to encourage light diffusion – light bouncing into shadier parts, giving better growth.

Putting it Up and Irrigation

This is obviously not a job for a windy, cold day and if you get nervous with flat-packs get someone else to do it. Some suppliers have staff to help and others have a DVD.

It is easy apparently, but will take a good two days and you will need three people at times as a minimum.

Fitting in warm weather means the polythene will hug more tightly and makes the job more pleasant.

Overhead watering systems might sound attractive, but the environment tends to be humid anyway and as you are growing a wide range of crops means some are too wet and some too dry. Seep hose selectively used can save hours though.

If you want to overwinter tender plants, an electric heater is the simplest solution. Perhaps I should bite that bullet now…

‘The Polytunnel Book: Fruit and Vegetables All Year Round’ by Joyce Russell, photographs by Ben Russell (Frances Lincoln, £16.99)

Buy reader offers at gardenshop.telegraph.co.uk

As the seasons change and even sunnier days arrive with that familiar autumnal nip in the air, I’m reminded of how my polytunnel really comes into its own. This structure covered in a thin layer of plastic is now invaluable to my growing efforts, providing protection against the lashing rain we had last week in West Wales and affording greater resilience in the battle against extreme weather that faces us for the foreseeable future.
It’s no wonder that polytunnel growing is on the rise. They are a lot cheaper to buy than a greenhouse and relatively easy to put up yourself. If you can fit one in, they really do take your fruit and veg growing onto a whole new level, widening the range of what you can grow successfully in the first place: you’ll be able to grow grapes, melons, cucumbers, peppers, aubergines and chillies. Plus it provides a delightful haven from the worst of the weather outside.

If you’re feeling tempted, spring is the best time to construct one in your garden or on your allotment, although there seem to be lots of discounts around now, so out of season may be a cheaper time to buy. You’ll need to situate your polytunnel carefully: a sunny spot on a level area with some protection from wind is preferable. As long as it isn’t more than 3m tall and doesn’t take up more than 50% of your garden, or cause an issue for your neighbours, planning permission is not normally required. If in doubt though, do check with your local planning department first.
Here are just some of the ways you will stand to benefit:

Year-round salads A polytunnel opens up a world of winter salad opportunities that you’d be hard-pushed to experience otherwise. More delicate lettuces and leaves will be better quality and keep going that bit longer, while hardier kales, chard, mustards, cresses, chicories, spinach, parsley and mizuna will keep you in exciting leaves for many months to come. If you’re quick, hardier salad plugs can still be planted out now. You can also try cutting back summer lettuces to reduce the risk of mildew and encourage slow winter growth.

Owning a polytunnel can open up a whole new range of crops, including grapes. Photograph: Kim Stoddart

Earlier crops With a polytunnel, the so-called hungry gap in spring isn’t as noticeable, as many crops including new potatoes, spring cabbage, peas, salad and beans won’t be far off at all. There is still time to germinate pea and broad bean seeds to enable you to overwinter plants for a real head-start come spring.

No need to be just a fair weather gardener No matter how dire the weather, you can garden or just sit and relax in your polytunnel. After the appalling weather last winter I’ve added a deckchair and little seating area in mine now – it really is a little sanctuary. Simply lay a weed suppressant layer covered with gravel over your chosen spot. This is the quickest (and one of the cheapest) ways to go about it.

In a good year, Kim Stoddart gets a bonus second batch of strawberries from her polytunnel plants. Photograph: Kim Stoddart

Best for strawberries I’ve never had a great deal of luck with strawberries grown outside. As soon as they near ripeness, birds, slugs and insects descend to munch on the majority of the crop before I can get stuck in. Inside is a completely different matter, with a bumper harvest each time. In good years we sometimes get a bonus second batch of strawberries from our plants later in the season, too. Now is a good time to get runners established; do so by carefully placing the new plants in pots with fresh multipurpose compost still attached to the parent plant.

Growing flexibility Even in an unheated polytunnel such as mine, you can still sow seeds significantly earlier than you would do otherwise. I also keep a large home-made unheated propagator on the potting bench to further aid germination and protect seedlings from the cold (and the polytunnel mice). Likewise, you can also sow a bit later than you would do normally, as the growing season is extended on both sides, providing all round greater flexibility. Plants such as cucumber, tomato and melon can produce fruit well into November and sometimes December depending on how cold it gets, so it’s well worth leaving them in the ground.

A helping hand for harder-to-grow crops I’d be hard pushed to grow decent tomatoes, cucumbers or peppers in my garden in West Wales without some form of cover. It also gives me room to experiment with more adventurous produce. The key here is making sure your polytunnel is clean inside and out to ensure your plants get as much light as possible, especially this time of year.

Seed saving If you’d like to extend your seed saving efforts, a polytunnel will help immensely. It allows you to safely overwinter more sensitive biennials such as carrots, parsley, beetroot and swede so they can successfully flower and set seed the following year. Now is a good time to take a few tomatoes, peas, french beans, cucumbers and the like and bury them in the ground so they can spring into action when they’re ready the following year. This really is lazy gardening at its best.

Winter protection for container plants Potted herbs such as rosemary, parsley, sage and thyme will benefit from being brought inside, rewarding you for their shelter with more opportunities for winter pickings. While any more sensitive plants can also benefit from being given a barrier against the elements. Just bring them inside and remember to keep watering.

  • For more resilient gardening ideas and antics see getbadlybehaved.com or @badlybehavedone

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