Potassium is a major mineral nutrient required in tomato plant. Applying potash can increase tomato yield obviously, especially in marketable yield. The content of soluble sugar, organic acid and soluble solid also increased when potash applied. Plant growth is restricted when potassium deficiency. The experiment on effects of potash applied at different growth phases on tomato yield and quality was conducted with tomato plants grown in pots in greenhouse. There were five treatments in this experiment: potash applied at seedling phase (treatment1); potash applied at flowering phase (treatment2); potash applied at fruit enlarging phase (treatment3); 40, 30 and 30% of total potash applied at seedling, flowering and fruit enlarging phases respectively (treatment4); no potash applied (CK). The results indicated that: potash promoted plant vegetative and generative growth significantly. Applying potash at flowering could obviously increase plant height and stem width, 11.4% and 4.4% higher than that of CK, respectively. Potash applied at flowering phase could obtain the highest yield and the total yield was 2.14 kg/plant, increased by 38.9% as compared with CK. Applying potash at seedling and SFE phases could also increase tomato yield to some extent, but it’s not the optimum phases for potash application, but applying potash at fruit enlarging phase was similar to that of the control plants. Potash applied at different phases on tomato quality was also investigated, significant difference appeared. The content of soluble sugar, organic acid and soluble solid were the highest among all the five treatments, significantly increased by 44.7%, 28.8% and 7.1% as compared with CK, respectively. Potash applied at fruit enlarging phase got the highest ratio of sugar to acid. From this result, we concluded that flowering phase was the optimum phase to applying potash with fruit of the highest quality. The effective potash applied at different phases on tomato vegetable growth, yield and fruit quality were discussed.

Kinds of Tomato Fertilizer

Effective tomato fertilizer, whether organic or not, provides nutrients tomatoes need at different stages of growth.


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What nutrients tomatoes need

To grow successfully, tomatoes need nitrogen, phosphorus, potassium, potash, calcium, and magnesium, along with other trace minerals.

It’s always best to have your soil tested to check for nutrient levels and pH. You can test your soil yourself, both its nutrient levels and its pH, in a simple, inexpensive soil test kit. Or contact your local extension office and ask about local soil testing services. Tou can also find simple (but accurate) pH test kits online.

Test results may show a particular nutrient deficiency. Then you can amend your soil appropriately. Soil nitrogen content should be higher than phosphorus content.

The next step is to select a tomato fertilizer.

How to read a fertilizer package

Most fertilizers are a combination of the three nutrients commonly fed to plants: nitrogen, phosphorus, and potassium (referred to as the “N-P-K ratio”). A commercial fertilizer’s analysis is listed on the label in a three-number series, such as 15-10-5. The three numbers represent those three nutrients. A 15-10-5 fertilizer contains 15% nitrogen, 10% phosphorus, and 5% potassium. The remainder of the fertilizer is filler material.

What fertilizer nutrient balance to choose for tomatoes

Nitrogen. Nitrogen encourages leaf growth, which is why fertilizers with higher ratio of nitrogen (the first of the three numbers) are an optimum choice for lawns and grasses. But in tomatoes, excess leaf growth discourages blossoms and fruit.

A complete fertilizer with a balanced supply of the three major nutrients, such as 10-10-10 or 5-10-10, is a better choice for tomato plants at initial planting time. Stay away from high-nitrogen fertilizers such as urea, ammonium sulfate or fresh manure, which will help produce dark green, tall tomato plants but fewer tomatoes.

Phosphorus. Phosphorus (the second number in the N-P-K ratio) encourages flowering, and therefore fruiting.

Potassium. Once a tomato plant starts flowering, it needs a higher ratio of potassium (the third number in the N-P-K ratio). Good organic sources of potassium are granite dust and wood ash.

Specialized tomato fertilizer

Two fertilizers specially formulated for tomatoes are :

Miracle-Gro Tomatoes (18-18-21), a crystal formula that is mixed with water and applied through a hose, sprayer, or sprinkler

Tomato Tone: (4-7-10 or 3-4-6): a granular fertilizer that is worked into the soil. Tomato Tone is organic and contains calcium, magnesium, sulfur and trace nutrients.

When to add nutrients during the tomato season

Once a plant is established in the garden, a phosphate-concentrated application (such as 0-46-0 commercial fertilizer) every 6-8 weeks increases tomato production. Bone meal, with an analysis of 4-12-0, is a good organic source of phosphorus. When a tomato plant sets fruit, start a systematic fertilization program and feed every three weeks until frost.

See more on our Fertilizing Tomatoes Pinterest board.

More about tomato fertilizer
How to use tomato fertilizer to get the best tomato production
Organic tomato fertilizer: advantages and disadvantages…
Epsom salts: a natural tomato fertilizer …
Does tomato fertilizer potency stay strong over time?
Tomato fertilizer question: will this fertilizer work for tomatoes?
More on growing tomatoes
Staking tomatoes produces a bigger, healthier harvest …
Watering tomatoes when planting and just afterwards …
Watering tomato plants: the basics …
Watering tomatoes: FAQs (Frequently Asked Questions) …
Techniques for watering tomato plants …
How and when to mulch tomatoes …
What’s the best mulch for growing tomatoes?
How to control weeds in the tomato garden …
Pruning tomato plants: how and when to do it …
Growing tomatoes: top 4 areas of tomato care …

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New! Comments

Have your say about what you just read! Leave a comment in the box below.

I usually add either seaweed, manure or both to some part of the garden depending on what I’m growing. This give me an all round fertile soil. I may need to add some amendments later on for hungry plants like tomatoes or courgettes but for the most part I can leave things as they are.

You may not have a ready supply of manure or access to seaweed so you will need to use some handier packaged products. We have a wide range of options to solve any problem all of which will be gentle on your soil. Just make sure you also add some bulky material every year, the best being your own home produced compost.

Liquid V’s granular or bulky feeds
In general granular or bulky feeds like seaweed, manure or compost take longer to have an effect as they need to break down n the soil first. Liquid feeds, on the other hand, are readily available to your plants and will have an immediate effect.

It is a good idea to apply bulky organic feeds at any time of year to improve the long term health of your soil. If treating a specific issue or to give a plant a boost it will be more beneficial to use a liquid. Remember a liquid doesn’t build the soil so they should always be used as a addition to your broader soil feeding regime.

The exceptions to this rule are container grown plants. They will always need direct feeding because of the limited root space available to them and the fact that they are growing in a simple growing medium like peat. Peat, coconut fiber or peat free compost has has very low nutrient levels so your plants will need a supplementary feed.

What is HIGH POTASH plant food?

flowerJust a note on Tomato Feed: They are very high in Potash (K) and initiate flowers and then tomatoes but tomato feed is also high in nitrogen (N) for growth. The high N is to balance the very high K (potash) which is very import for tomatoes, this means it can be too ‘strong’ for other plants. If you would like to use it for other plants dilute it by 50%.

Nitrogen encourages green growth, Phosphates (phosphorous in soluble form) is essential for healthy growth and good for roots, Potash (potassium in soluble form) not only produces more flowers and good fruit but also, makes plants tougher and resistant to diseases and pests.

Last of all, if you feed too much with high N or balanced feeds you may stop flowers forming (why would they need to flower? They are happily growing away). If this is the case stop using these feeds, water with plain water for a week or two & then feed with the high potash food.

Still not sure? Call us on air on BBC Radio Sheffield between 9 & 10 am every Sunday on 0114 279 6699.

Keep both of the following as essential ‘tools’ for successful gardens and plants.

When I first started growing my own fruit and veg in containers, I found information about how, when and what to feed plants in containers surprisingly hard to come by. Perhaps this isn’t surprising. Crop nutrition is never going to be a sexy subject. At its best it’s a complicated and slightly smelly one. Still, if you want your plants to thrive in containers, you need to put a bit of thought into feeding them. You can dedicate a lifetime to learning about crop nutrition. But I’ve found a little knowledge can go a long way.

Plants need a mix of nutrients, just as humans need to consume a mix of protein, fat, carbohydrate, minerals and vitamins. They particularly need nitrogen (N) for leaf growth, phosphorus (P) for root growth, and potassium (K) for fruit growth. All plants need all three, but leafy crops particularly need nitrogen, and fruit crops won’t develop well without enough potassium. They also need a wide range of other nutrients, often in tiny quantities. I think of these as the equivalent of the vitamins and minerals we need to keep us healthy. Finally, plants need bacteria and fungi in the soil to break it down and release food to their roots, just as humans need bacteria to digest food in our guts.

Most compost or growing mixes you can buy in garden centres only contain enough nutrients for six weeks’ growth. So for optimum results, you need the right fertiliser (rich in either nitrogen or potassium) and you need to make sure the plant has enough vitamins and minerals and that there is plenty of soil life in your pots.

Here are some of the easiest ways to add these critical ingredients.


Your salads and other leafy crops won’t flourish unless they have enough nitrogen.

Chicken manure pellets are cheap, easy to source, and contain most of the essential nutrients for plants. They are particularly high in nitrogen. I use them all the time for rejuvenating old compost to grow salads. Simply mix a handful into your compost before you plant your salads.

If you have a supply of nettles nearby, you can make nettle tea by soaking nettles in a bucket of water for two weeks. The resulting brew is high in nitrogen and other goodies (if a bit whiffy!).

Take care not to add too much nitrogen to fruiting crops – you may get lots of leaves and not many fruits. Try experimenting – a little bit at a time is the safest strategy.


To get good yields of tomatoes, runner beans, squash, chillies, strawberries and other fruiting crops from containers, you need to regularly add additional potassium (K).

The easiest way to do this is to buy a bottle of tomato feed. Although called tomato feed, this will do the job for all fruiting crops.

You can also make an excellent potassium feed by soaking comfrey leaves in water for a week to make comfrey tea, which is a more organic solution. You can find comfrey alongside canals and in town marshes where it can grow wild in abundance – or you can buy liquid comfrey online. This is wonderful stuff, though it is even smellier than nettle tea.

Vitamins and minerals

Liquid seaweed is an excellent source of vitamins and minerals. You can add it to your watering can once a week to keep your plants healthy. Or, to make a precious bottle go further, you can spray it on to the leaves of your crops using a simple hand spray (an empty spray bottle, cleaned well, works perfectly).

Rock dust (available in some garden shops) is another source of minerals – mix a few handfuls into the soil in each container.

Soil life

Healthy soil contains an invisible and amazing array of bacteria and fungi which digest the nutrients you are adding, releasing it to the roots of your hungry plants.

You can buy various products such as mycorrhizal fungi to add life to your pots. But one of the best sources is worm compost or worm tea. You can make this at home in a wormery.

Worm compost

Worm compost is fantastic for containers: as well as soil life it’s rich in the vitamins and minerals your plants need, as well as some of the major nutrients. Mix 10 – 25% into old compost to rejuvenate it, or add 5 – 10% to new compost to add soil life. Add a layer of an inch or two to hungry crops like courgettes and tomatoes to give them a boost half way through the growing season.

How much to feed?

Feeding crops is as an art as well as a science. How much you feed depends on lots of variables: the size of pot, what compost you’re using, how big your plant is, and how fast it’s growing. The secret is to give it a go, observe the difference, and learn from the results. As a general rule, little and often is the safest strategy (too much feeding is as bad as too little). And feed more when your crops are fruiting.

I’m only scratching the surface of a big subject here – but following these simple rules can, in my experience, transform small harvests into more significant ones.

Interested in finding out more about how you can live better? Take a look at this month’s Live Better challenge here.

The Live Better Challenge is funded by Unilever; its focus is sustainable living. All content is editorially independent except for pieces labelled advertisement feature. Find out more here.

What Is Potash: Using Potash In The Garden

Plants have three macronutrients for maximum health. One of these is potassium, which was once referred to as potash. Potash fertilizer is a natural substance that is constantly recycled in the earth. Exactly what is potash and where does it come from? Read on for these answers and more.

What is Potash?

Potash got its name from the old process used to harvest potassium. This was where wood ash was separated in old pots to soak and the potassium was leached from the mash, hence the name “pot-ash.” Modern techniques are a bit different from the old pot separation mode, but the resulting potassium is useful for plants, animals and humans.

Potash in soil is the seventh most common element in nature and is widely available. It is stored in soil and harvested as salt deposits. Potassium salts in the form of nitrates, sulfates and chlorides are the forms of potash used in fertilizer. They get used by plants that then release potassium into their crops. Humans eat the food and their waste deposits the potassium again. It leaches into waterways and gets

taken up as salts which go through production and are used again as potassium fertilizer.

Both people and plants need potassium. In plants it is essential for water uptake and for synthesizing plant sugars for use as food. It also is responsible for crop formulation and quality. Commercial bloom foods contain high amounts of potassium to promote more flowers of better quality. Potash in soil is the initial source for the uptake in plants. The foods produced are often high in potassium, such as bananas, and afford a useful source for human consumption.

Using Potash in the Garden

The addition of potash in soil is crucial where the pH is alkaline. Potash fertilizer increases the pH in soil so should not be used on acid loving plants such as hydrangea, azalea and rhododendron. Excess potash can cause problems for plants that prefer acidic or balanced pH soils. It’s wise to do a soil test to see if your soil is deficient in potassium before using potash in the garden.

The link between potash and plants is clear in the promotion of bigger fruit and vegetable yields, more abundant flowers and increased plant health. Add wood ash to your compost heap to increase the potassium content. You can also use manure, which has a small percentage of potassium and is relatively easy on plant roots. Kelp and greensand are also good sources for potash.

How to Use Potash

Potash doesn’t move in soil more than an inch so it is important to till it into the root zone of plants. The average amount for potassium poor soil is ¼ to 1/3 pound of potassium chloride or potassium sulphate per 100 square feet.

Excess potassium accumulates as salt, which can be damaging to roots. Annual applications of compost and manure are usually sufficient in the garden unless soil is sandy. Sandy soils are poor in organic matter and will need leaf litter and other organic amendments tilled into the soil to increase fertility.

Fertilizing Tomatoes

Tomatoes need quite a big food supply over the season — they’re what we call “heavy feeders.” This is no surprise when you look at all the work they’re doing: extending the stem, putting out more branches, leaves and blossoms; developing, nurturing and ripening all those fruits! To do all this work they need a steady diet of water and nutrients.

All About Side-Dressing

In most gardens, it’s a good idea to side-dress tomatoes. That simply means placing fertilizer around the plants to give them extra nourishment through the season. One or two side-dressings is fine for most gardens.
Many kinds of fertilizers can give tomatoes the extra nutrients they need. Some gardeners prefer to use a complete fertilizer (such as 5-10-10 or 10-10-10). Organic fertilizers such as bone meal, dried manure or cottonseed meal are also good. Just remember that most organic fertilizers don’t contain balanced amounts of the three major nutrients – nitrogen, phosphorus and potassium. For example, manure tends to be low in phosphorus so you could add bone meal at the same time to provide a more complete diet.
Stay away from high-nitrogen fertilizers such as urea, ammonium sulfate or fresh manure because it’s easy to use too much. When you over fertilize, you get tall, dark green plants with few tomatoes.

When To Side-Dress

Start side-dressing when the first tomatoes have just formed – when they’re about the size of golf balls. Make repeat side-dressings every three weeks after that. About a pound (two cups) of 5-10-10 should be enough for all the plants in a 30-foot row (about 20 plants). This works out to about 1-1/2 tablespoons per plant spread in a one-inch-deep circular furrow five to six inches away from the stem, usually right under the drip line of the plant. Be careful not to get any of this fertilizer on the leaves or stem because it will burn them. Cover the fertilizer with one to two inches of soil. The next rain or watering will start carrying the nutrients down into the root zone of the plants.

To feed or not to feed our flowering plants?

That’s the question Peter Dowdall poses this week on foot of new research into the life cycle of garden plants.

It’s the time of year that we need to keep feeding our flowering plants to extend their display.

Getting the best out of hanging baskets, window boxes and patio planters means feeding with a good liquid feed. Perennials too and roses will all benefit from dead heading and some fertilising.

Or will they? Is it all just a myth? A marketing ploy to keep us gardener’s buying plant feeds and fertilisers. Do they actually make any difference and if so which one should we use? Good gardening advice has always been that we should feed the soil and not the plant. The logic being, obviously, that if the soil has everything that the plant needs to thrive, then you shouldn’t have to add specific feeds.

For years gardeners like myself have been using and recommending high potassium feeds such as tomato food and sulphate of potash to encourage flowering but there is much debate at the moment as to whether potassium actually has any discernible effect on promoting flowers.To understand what plants need, it is important to have a grasp of the different nutrients and what each provide to plants.

Nitrogen is necessary for leaf production and green colour, phosphorous is important in root development and potassium regulates water and nutrient movement in plants and also has an effect on fruit production. Magnesium and iron are necessary for green leaf colour. When you look at a plant fertiliser you will see the NPK analysis on the packaging, this will tell you the ratio of nitrogen to phosphorous to potassium.

The Royal Horticultural Society (RHS) advises using potassium, but there have been many studies and trials undertaken that show potassium has no effect on flowering and its all just a myth.

It is certainly true to say that nutrients don’t promote flowers — hormones do and potassium is not a hormone so it cannot promote flowers. However, if a plant is suffering from a potassium deficiency then this will lead to stunted growth and this may limit flowering because the plant cells can’t divide to allow the growth.

There is no doubt that a potassium deficiency will reduce the quality of flowering and thus a potassium feed will improve the quality of the blooms, but there is little or no evidence to suggest that it will increase the number of flowers.

Why then have gardeners for generations used and still use, high potassium feeds to encourage flowering? Perhaps it’s because potassium is essential for the development of over 50 soil enzymes so the argument isn’t as clear cut.

There is still much in the world of nature and under the soil that we do not understand. So let me stay on the garden fence on this one, maybe the benefits of potassium as a plant food have been overstated or maybe nature still has much to tell us.

Let me tell you something about my friends the earthworms. They work like mini processors, ploughing through the soil, aerating and improving its texture. Up they come to the soil surface and munch away on pieces of leaf mould and other garden debris, regurgitating it as worm cast. Earthworms have been used in trials for sewage treatment plants and in this waste there are traces of heavy metals. When a worm feeds on the waste, there is no trace of heavy metals in its cast. There are traces of these same metals in the worm but when that worm dies he is devoured by another worm and there are no traces of these metals in the new worm. The more I work in the garden and the more I learn, the more I am aware of how much I have still to learn and how much I will never know.

I am a great believer in the logic of feeding the soil as opposed to the plant and I would encourage all gardener’s to invest in a wormery or worm composting bin.

The main feeding that my soil gets is what my worm bin produces in both worm casts and also the liquid ‘worm tea’ that is produced.

Both the casts and the liquid are extremely high in nutrient value but also, and more importantl,y they are probiotic which means that by adding them to the soil they will stimulate the beneficial bacteria and micro organisms already present. A wake up call to the soil if you like.

Worm tea is widely available in a locally produced product called Liquid Gold so even if you don’t fancy setting up the worm processing unit, help is still at hand.


Keep an eye out now for tell tale signs of vine weevil damage. Leave s of susceptible plants will be eaten from the outside in with tell tale signs. If you can remember the old weekly bus tickets that we used to get long ago — each day the conductor would punch a piece from the side. Well, that’s what a leaf looks like once the vine weevils have attacked — a well used weekly bus ticket.

It’s the adult beetle that causes this damge but the damage done by the larvae is more insidious and much more harmful.They will feed on the roots of host plants and their attack results in weakened growth and a plant loose in the soil.Because they are unseen, the damage is done before it is spotted.

Go online to supernemos.ie and read about this Irish-developed product and apply it to your garden now to eradicate this cursed pest.

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