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Understand How Cold Temperatures Affect Citrus Trees

By Dr. William Johnson, Extension Horticulturist, Galveston County Texas AgriLife Extension Service

Many gardeners have inquired about the susceptibility of citrus to cold temperatures. The winter season has been tough on citrus plants.

It is important to understand how cold temperatures affect citrus trees. Among the citrus types most easily killed or damaged by freezing weather are citrons, lemons and limes. Temperatures in the high 20s will kill or severely damage these plants.


Some gardeners who protected their citrus trees during
the recent cold snap were surprised to see their plants
setting flower buds as temperatures started to warm.

Sweet oranges and grapefruits are somewhat more cold-hardy and usually require temperatures in the mid 20s before incurring major damage to large branches.

Tangerines and mandarins are quite cold-hardy, usually withstanding temperatures as low as the low 20s without significant wood damage.

But, among the edible types of sweet citrus, the satsuma and kumquats have the greatest degree of cold hardiness. Properly hardened bearing trees will withstand temperatures as low as 20 degrees Fahrenheit without appreciable wood damage.

Temperatures at ground level can be several degrees lower than temperatures around the canopy of the tree, especially if there is no wind.

Keep in mind the temperature ranges given above only refer to leaf or wood damage. Citrus fruits easily freeze at 26 to 28 degrees when these temperatures occur for several hours.

A longer duration of freezing temperatures is required to freeze grapefruit compared to sweet oranges.

The particular temperature at which tissue of a given plant will freeze and the degree of the damage sustained are functions of a number of factors in addition to the species and variety involved.

Some of the more important are:

  • The freezing temperature reached;
  • The duration of the minimal temperature;
  • How well the plant became hardened or conditioned before freezing temperatures occurred (the freezing point of tissue of a hardened citrus plant might be 5 to 6 degrees lower than an unhardened plant);
  • Age of plant (a young plant cannot withstand as much cold as a more mature tree); and
  • Healthy trees are hardier than diseased trees.

Another complicating factor contributing to observations by some that citrus plants seem to freeze at higher temperatures in some years is the difference between air (ambient) temperatures and leaf (tissue) temperature.

On a windy night with clear or cloudy skies, leaf temperature will be about the same as air temperature. On a cold, clear night with little or no wind movement, however, leaf temperature can easily drop several degrees (3 to 4 degrees) below the air temperature because of supercooling caused by frost.

Thus, under the latter circumstances, while the minimum air temperature on a given night may have only been 25 degrees, actual leaf temperature of the plants may have reached 21 to 22 degrees.

The critical temperature is that of the leaf or fruit and not the ambient air temperature.

Trees with a good fruit crop are less hardy than those with no fruit.

Research data provided by Louisiana State University indicated trees growing on bare ground have a higher probability of survival than trees growing in turf areas.

The heat from the ground can radiate upward into the canopy of trees. The difference in the canopy of the tree can be up to 5 degrees.

In general, it is recommended citrus trees be protected when the temperatures is expected to go below 27 degrees for an extended period.

The good news is before the cold snap, temperatures had been on the cool side for a while and citrus trees had hardened off and were fairly dormant.

Citrus trees can better withstand cold weather when they are dormant.

No immediate action is needed when freeze injury is suspected. There is no benefit to pruning the plant until spring growth commences, and the full extent of injury is manifested. Pruning might actually be counterproductive by stimulating faster bud activity before the danger of additional frost/freeze events has truly passed.

Dr. William Johnson is a horticulturist with the Galveston County Office of Texas AgriLife Extension Service, The Texas A&M System. Visit his web site: Gulf Coast Gardening.

Return to HortUpdate – March 2011 Index

Tips for Overwintering Citrus Trees

Watch our top 10 tips for looking after citrus and learn how to get the most from these rewarding plants.

As the weather and day length changes, so does the care that your citrus trees need. Because sometimes people can be caught out by this, we’ve put together our top 5 tips to remember for the winter season.

STOP PRESS: At the end of January the days are already starting to get longer, bear this in mind when you are thinking about watering and we’ll update this page again at the end of February.

1. Watering

As the temperature drops water evaporates more slowly but also because your citrus tree is no longer putting on new growth, the amount of water your tree will need will be considerably less in the winter months.

As always water heavily from the top of the pot and let the excess water drain away. Don’t let your citrus tree stand in water and don’t water again until the top of the soil starts to feel dry to the touch.

In our Nursery we have gone from daily watering in summer, to twice weekly watering in autumn to once every 7-10 days at the moment. How quickly the top of the soil dries out for you will depend on the position and temperature you are keeping it in and even the size of the plant compared to its pot.

2. Position

We all love sunshine, citrus more than most. Remember most citrus prefer to be above at least 5C in the winter. That means the coolest but very lightest place you can find indoors.

Citrus trees fall into 3 main categories for hardiness:-

Non-hardy Calamondins, Sweet Oranges, Kumquats, Tahiti Limes, Grapefruits and Mandarins should be kept above 5C and it’s best to move them inside before the night time temperature drops much below this and wait until late Spring before they go back outside. Choose the sunniest place in the house away from draughts and radiators.

Nearly hardy Lemon trees, Chinottos and Kaffir limes will be fine in temperatures right down to zero and will even tolerate -1C or -2C for short periods. This winter has been quite mild so far so we know many people have chosen to keep their trees outside. In wet weather do just make sure that your tree is not sitting in a puddle of water and that it protected from the worst downpours. Keep an eye out for any hard frosts and remember it’s not the leaves you need to worry about but the rootball – this must not freeze!

You can wrap the pot with hessian or fleece to extend the season outdoors and/or bring it close to the wall of your house to give your tree a bit of extra protection. When you think it is going to be too cold overnight it’s best to move your tree to a new position for the coming months rather than try and move it in and out and every day.

Hardy Yuzus and Finger Limes can withstand temperatures down to -15C. It’s still best to keep these in a pot as they will suffer if they become too waterlogged, but these hardy varieties are grown on Poncirus trifoliate stock and should withstand all that a British winter can throw at them.

In the middle of winter our dark, rainy days can lead to some leaf drop even if you are doing everything right. Kaffir Limes, Kumquats and some Lime trees seem most susceptible to this and once the days start to get longer they will pick up and put on new growth. In the meantime try to ensure they are getting as much direct sunlight on their leaves as possible.

Indoors you don’t need a conservatory but just a nice big window to place your tree or trees beside. Try to choose a place that is free from draughts and away from any radiators (especially under floor heating) and where the temperature is reasonably constant. Most citrus will overwinter very well even in quite warm houses but if your tree does start to suffer mid winter, hang in there – spring is just around the corner.

3. Winter Feed

Citrus benefit from a balanced Summer and Winter Citrus Feed. This is in addition to the free plant tonic we include when your tree is delivered.

The Summer Feed has more Nitrogen for leaf growth and the Winter Feed has proportionately more Phosphorous and Potassium to help develop fruits. At this time of year you should be using a Winter Feed every other watering to keep your tree at its best.

You should be able to buy citrus feed from a good garden centre or of course you can buy the citrus feed we use for £6.95 and have it delivered free of charge. Buy winter feed

4. Watch for Leaf Drop

Citrus trees are not deciduous. One or two leaves is not too much of a concern but more than this and it’s a sign that your tree is unhappy. This is almost always to do with too little or too much water and sometimes it can be tricky to know the difference. If you’re not sure which you are always welcome to give us a call on 01825 721162 and we’ll do our best to advise you.

Other things that can cause leaf drop are sudden or dramatic changes in temperature, under floor heating or being too near to a radiator or being in too draughty a position – but again if you’re not sure – do get in touch.

January and February are the toughest months of the year for citrus trees when overcast skies and short days mean they are surviving on minimal light for weeks on end. Some varieties are tougher than others but we find even in our greenhouses with maximum light, some of the limes particularly, will develop a bit of leaf drop at this time of year.

Once the days get longer, this will settle down and they will soon replace these leaves with fresh foliage in the spring. If your tree has lost more than a handful of leaves do give us a call though and we’ll just check through that there is nothing else that you can do.

5. Treat early for Pests

Outdoors birds and other insects plus the cooler temperatures will keep most pests at bay. However, indoors over winter, the warm conditions can become breeding grounds for pests.

Scale, mealy bug, red spider mite, aphids and caterpillars all do like citrus trees but the trick is to catch them early. Round brown circles, white sticky fluff, webbing, holes in the leaves or stickiness are all signs of pest attack and should be treated as soon as possible. A soapy washing up liquid solution is normally good enough if the infestation hasn’t got too advanced. Spray on to the leaves morning or evening a few times a week until it’s cleared.

If you are not sure what is attacking your plant then why not send us a picture by email or give us a call and we’ll be more than happy to help you identify any problems.

And finally…. don’t forget to enjoy the fruits of your labour!

Although citrus don’t always follow a strict fruiting season in the UK, they do usually fruit in the winter months. Lemon Meyers, Limes, Grapefruits, Kumquats and Clementines will naturally drop when they are ripe, but Lemon4seasons, Calamondins and Chinottos will need to be picked off the tree when they are fully coloured.

Don’t forget citrus are not just for your G&T. Try a slice of lemon in hot water for a healthy alternative to tea or coffee or try using sour Oranges and Kumquats in place of Lemons in your favourite recipes. Packed with vitamin C, all citrus are brilliant for keeping away winter colds but if you find them a little sour on their own, juice even the sourest Oranges with a bit of fizzy water and sugar and they make a super refreshing and healthy drink – way tastier than wheatgrass!

For more information about pruning, repotting and year round care

Meyer Lemon Trees: 7 Secrets for Tons of Fruit

The Meyer Lemon Tree is a fun tree that always seems to be blooming or fruiting. Many Meyer Lemon Trees are blooming now, bringing beautiful flowers and a wonderfully fresh citrus scent to many homes.

The Meyer Lemon Tree is a fun tree that always seems to be blooming or fruiting. Many Meyer Lemon Trees are blooming now, bringing beautiful flowers and a wonderfully fresh citrus scent to many homes. What’s a better way to prepare for spring cleaning than with an all-natural lemon scent?

The Secrets of Meyer Lemon Trees

Lemon blooms turn into fruit, so if you don’t have blooms, life won’t give you lemons. So, how exactly do you get these blooms? Make your tree comfortable. Under the proper care conditions, your tree will have a ton of blossoms!

1. Light

Before fruiting, Meyer Lemon Trees need to see the light! They won’t flower without getting enough light. Make sure your trees get at least 6 hours of sunlight a day. You can do this by placing your tree by a large, sunny window. If you can, try to place your tree near an area that faces South. Southern-facing areas tend to get more light.

Also, if your tree is potted and kept indoors, rotate it every three weeks. This way, the entire tree gets time in the sunshine!

2. Watering

Next, make sure that your trees get the right amount of water. Overwatering or under-watering your tree can harm fruit production. The soil should slightly dry in between waterings, but it should never be completely dry. Check on your soil once a week. If it feels dry to the touch 2 inches below the surface, it’s time for more water. Slowly pour water into the pot and count to 20, or wait until you see water running out of the bottom of the pot.

Generally, Meyer Lemon Trees need water every one to two weeks. Leaves can be an indicator as to how your tree feels. If the leaves are drooping like they’re too heavy for the branches, the tree is getting too much water. If the leaves are crispy and dry or curl upwards, this is a sign of under-watering.

Don’t immediately overcorrect under-watering. Gradually add more water to your tree over time. If you immediately saturate the soil with a ton of water, your tree may become stressed.

3. Nutrients

Another way to keep your tree healthy and productive? Make sure that it gets all of its vitamin and minerals. When potting or planting your tree, it’s beneficial to mix in some citrus planting mix with your natural soil.

Also, to give your tree an extra boost, give it some citrus fertilizer! Give your tree two tablespoons of fertilizer three to four times per year. Once in the early spring, once in early summer, then again in the late summer and in the fall. Space out your fertilizing by about four to six weeks.

4. Temperature

Meyer Lemon Trees are very cold hardy and can withstand temperatures down to about 20 degrees. If your area gets colder than that, your tree will need to be brought inside.

But when they’re inside, winter heat can dry them out. Be careful not to place them under a vent. If your leaves start to dry, you can mist them daily with a spray bottle for extra humidity.

Once it warms up, don’t just stick your tree out in the hot sun for hours! It will need time to adjust to the heat. Move your tree outside for a few hours each day, gradually increasing the amount of time it spends outdoors, before letting it live outside all summer.

5. Pollination

Once the blooms open on your tree, they’ll need to be pollinated. Good thing that these trees are self-pollinating! However, having two or more trees will greatly increase the amount of pollinated blooms.

Meyer Lemon Trees can bloom all year, but they have two main blooming times: fall and early spring. If they bloom while it’s too cold for them to be outside, simply keep your tree indoors. However, they won’t have the wind and bees to carry their pollen from bloom to bloom for them. You could release a few bees inside of your home to help with pollination, but we wouldn’t recommendit!

However, you can pollinate your indoor trees by hand. Simply take a small, dry paintbrush, and run it over each bloom as if you’re painting them. Do this once daily, and don’t wash the paintbrush until after the blooms have been pollinated.

6. Pruning

Another way to keep your Meyer Lemon Tree happy is by pruning it. Meyer Lemon Trees don’t have to be tall to produce fruit – just healthy. Keep them wide and branched out. When you decide to prune your trees in the early fall or early spring, look for branches that are growing straight upwards.

Generally, these aren’t fruit-producing branches. Also, remove any damaged or crossing branches. Make your cuts at 45-degree angles facing upwards to promote new growth.

Also, look for areas that block the sunlight from the center of the tree. Removing these branches will increase air circulation and the amount of sunlight that hits these branches, which will decrease your tree’s risk of mold and fungi.

Be sure to look at the number of lemons you have growing. In order to prevent fruit overbearing, you’ll want to remove a few lemons in large clusters when they’re pea sized. This will ensure that you have a few lemons that grow to their large, mature sizes, instead of a ton of lemons that stay small.

7. Patience is a Virtue

Your Meyer Lemon Tree will need time to get adjusted to its new environment before it starts producing fruit. Once your lemons start to grow, give them time to mature. They can take around six months to mature. Don’t harvest them until their skin changes from green to dark yellow. When your sweet Meyer Lemons are ready, their skin will be a shadeof yellow that’s similar to the color of an egg yolk.

How to plant and grow Citrus

GROW YOUR OWN FRUIT

Plant Information – Citrus (764 KB)
First plantings in the garden usually include at least one citrus plant – usually a lemon. Citrus overall embraces an interesting and attractive range of plants from more ornamental dwarf types to the larger and more commercially productive varieties. Unfortunately, because they appear non-complaining, citrus is usually left to look after itself; however, they do require some care. The following notes are a guide to situation, feeding, caring and ensuring the health of these wonderful plants.

SITE / POSITION FOR CITRUS

A position protected from winds and heavy frost in full sun is ideal. Without as much sun, they will not set as much fruit but for the home gardener this may still be sufficient.

SOIL FOR CITRUS

A deep, friable slightly acidic loam soil type is best for the citrus. They will grow in light or heavier soils provided some soil preparation is done. Light soils will require some additional WATERWISE CRYSTALS and a MUSHROOM COMPOST or COW & COMPOST MIX to help retain moisture and add nutrient to the soil. Heavy soils may require mushroom compost and organic matter to aerate, as well as GYPSUM CLAY BREAKER to open soil and ensure sufficient drainage. Good drainage is essential for citrus.

PLANTING CITRUS

Make sure the root-zone is moist before planting and then thoroughly water in after placing in position. Be careful to keep the tree level with the surrounding soil. Soil build-up around the trunk can cause collar rot. If you have clay soil, do not dig into this. Raise the bed or plant the tree as above the subsoil clay level if possible. By digging into it a pool can be formed which will collect water below the surface and kill the tree.

WATERING CITRUS

Citrus are not deep-rooted trees and thus require watering regularly.
Mostly their roots will be 1.2m to 1.5m below the surface. Care must be taken to ensure they have adequate watering during the hot summer months. In addition, be sure not to over water either.

MULCHING CITRUS

Mulching in spring helps conserve moisture around citrus trees in the hot summer months. A combination of MUSHROOM COMPOST, COW & COMPOST and WATERWISE CRYSTALS or PEAT MOSS will provide excellent moisture holding capacity. Do not build up mulches too closely around trunk. It is advisable to remove the previous year’s mulch before putting a new one down. Do not dig around citrus trees as their feeding roots are close to the surface and they resent disturbance.

FERTILISING CITRUS

In ground citrus should be fed with DINOFERT CITRUS FOOD during the warmer months with 1 application. Citrus also responds to applications of DYNAMIC LIFTER and COW MANURE, thus encouraging healthy growth.
For container growing, it is advisable to feed using OSMOCOTE TREES, SHRUBS & CITRUS or BRUNNINGS CITRUS FOOD during the warmer months, or a soluble solution of THRIVE SOLUBLE FLOWER & FRUIT.

PRUNING CITRUS

Pruning is really only necessary to remove dead wood and to cut out branches that are rubbing against each other. There is some advantage in training young trees to produce evenly spaced branches to allow light penetration into the centre of the tree.
Citrus that have become too tall may be pruned back severely, make sure you cover the wounds with a tree wound dressing such as STERIPRUNE. It is advisable to ‘skirt’ trees. This means removing all shoots to a height of at least 45cm to avoid disease problems, which may occur if branches are able to touch the ground. Remember to remove all shoots that come from below the graft. These shoots may occasionally arise from under the stock and if not removed will grow more strongly then the graft and eventually kill it. Thus, a tree that started as an orange may end up producing lemons, which is the type of under-stock.

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Edible Landscaping – How to: Grow Citrus in a Container

Select citrus tree varieties that naturally stay dwarf in containers. It will be easier to care for them and move them in and outdoors in cold climates.

‘Improved Meyer’ lemon is an excellent container citrus selection. The plants stay small and the fruits will grow and mature even indoors in a cold climate.

There’s nothing like the taste of fresh citrus fruits picked from your own trees. However, unless you live in citrus country (California, Florida, Texas, Arizona), then you’re probably going to have to get creative about growing it. The best way to grow citrus in colder climates is in a container. Even if you live in citrus country, container growing makes sense. It keeps the trees dwarf and compact, and makes the plants easier to manage. Newer varieties are better adapted to container culture, and many varieties are self-fruitful, so you don’t need to worry about pollination.

Even if you live in a climate where it will be difficult to get ripe fruit from your citrus tree, there are always the sweet scented flowers that bloom year round and make citrus a favored houseplant as well.

Here are the basics on how to grow citrus in containers.

1. Select the Right Plants. Although any citrus tree can grow in a container, full sized grapefruit or orange trees may be hard pressed to survive many years even in a large container. Look for dwarf varieties of citrus, such as ‘Improved Meyer’ lemon, ‘Bearss’ lime, ‘Kaffir’ lime, kumquats, ‘Trovita’ orange, ‘Calamondin’ orange, and ‘ Buddha’s Hand ‘ orange for container growing. These tend to stay between 6 and 12 feet tall at maturity outdoors and can be kept even at a smaller height in a container. In cold areas the ‘Improved Meyer’ lemon, ‘Calamondin’ orange, and kumquats are good choices since they’re most likely to fruit indoors.

2. Select a Good Container. Start with a small container when planting a young citrus tree since it will be easier to maintain proper soil moisture than in a big container. If the soil stays too wet in a large container, the young tree with a small root system may rot and die. A new citrus tree will grow fine in an 8-inch diameter container to start. Two to three year old trees will need a 10 to 12 inch diameter container. Eventually, you’ll need a 16 to 20 gallon container or one-half whiskey barrel-sized container for long term growth.

Select plastic, terra cotta, or wooden containers. Be sure they have adequate drainage holes. Plastic containers are the lightest weight and easiest to move in and outdoors with the seasons. However, the glazed terra cotta containers look more attractive when the plants are being grown indoors as houseplants.

3. Select the Right Soil Mix. Citrus need well drained soil, so selecting the right potting mix is important. Commercial potting mixes with peat moss, perlite, vermiculite and compost are fine to use as long as the soil is light enough to drain water well. If your soil is still too heavy, try adding hardwood bark chips to the mix to increase the amount of air spaces.

Even if you can’t get your citrus to fruit, the sweetly scented flowers leave a perfume that will fill a room.

Kumquats offer many small, tangy and sweet tasting fruits on rounded trees that are adapted to container growing.

4. Potting Up the Tree. Place bare root trees in the container, gently packing in soil around the roots to remove air spaces. Plant so the citrus roots are just below the soil surface, but the crown is just above it. If transplanting an existing citrus tree into a larger container, remove the old tree and examine the roots. Cut off any dead, broken, and circling root and repot. Water well.

5. Watering. Citrus prefer infrequent, deep watering as opposed to frequent shallow watering. Water when the soil is dry to 6 inches deep. If the leaves are wilting and perk up after watering, then you waited too long to water. If the leaves are yellowing and cup-shaped, and don’t perk up after watering, then you have been overwatering. Usually once or twice a week is a good frequency to water, but adjust it based on the time of year and weather. Cool cloudy conditions in winter will necessitate less frequent watering than hot, sunny summer conditions.

6. Fertilizing and Pruning. Fertilize in spring with a citrus plant food. Citrus need extra nitrogen, so look for formulations with double the nitrogen compared to phosphorous and potassium. If you can’t find citrus plant food in your area, timed-released or organic fruit tree foods with micronutrients are good alternatives. These slow release products will feed the plant over time. If the leaves yellow and the watering is correct, supplement the granular fertilizers with occasional foliar sprays of fish emulsion.

Prune off any new shoots that arise from below the graft union. These are rootstock shoots and won’t grow into the desired citrus variety. You can also remove thorns if you wish to make handling the tree easier. These will gradually diminish as the citrus tree ages. Prune for shape and balance in spring, removing errant or leggy branches.

7. Pests. Control aphids, scale, and mealybug pests by hand picking them, dabbing mealybugs with cotton swabs dipped in rubbing alcohol, spraying insecticidal soap on aphids, and horticultural oil on scale.

8. Winter Care. In cold winter areas, bring citrus indoors when temperatures dip into the 30Fs. Slowly transition the trees to the indoor/outdoor environment in spring and fall by bringing them in and out for one week. Place potted plants in a sunny south-facing window, reduce watering and consider placing a humidifier or other houseplants around to keep the humidity high during the dry months. In warm winter climates, protect trees left outdoors from the occasional frost with Christmas lights, blankets or burlap.

More information on growing citrus in containers:

Growing Citrus in Containers

Soil Preparation for Citrus Trees

Preparing your soil before you plant will greatly improve your plant’s performance and promote healthy, vigorous growth. It is a good idea to have your soil tested to determine if it is lacking in any essential minerals and nutrients. This can be done through your County Extension Office or with one of our digital meters.

The goal of soil preparation is to replenish vital minerals and nutrients, as well as break up and loosen any compacted soil.

NOTE: This is part 5 in a series of 11 articles. For a complete background on how to grow citrus trees, we recommend starting from the beginning.

When To Prepare Your Soil

Soil preparation can be done at any time that the ground is not too wet or frozen. Your trees may be planted even when temperatures are quite cool. If a hard frost is expected, it is advisable to delay planting for a while until temperatures become more moderate. Generally, as long as your soil is workable, it is fine to plant.

How To Prepare Your Soil

  • Roots grow faster when they’re spread out. Dig the hole deep and wide enough so the root system has plenty of room to easily expand. Keep the topsoil in a separate pile so you can put it in the bottom of the hole, where it’ll do the most good.
  • To loosen the soil, mix dehydrated cow manure, garden compost or peat moss (up to 1/3 concentration) into your pile of topsoil. Make sure the peat moss you get is either baled sphagnum or granular peat. You can also add our Coco-Fiber Potting Medium or 2 or more inches of organic material and work in evenly with the existing soil.

Your lawn can provide you with ideal organic materials such as grass clippings and shredded leaves. Not only will the grass and leaves break down to provide soil nutrients, but they will help loosen the soil as well. You can gather these in the fall with spring planting in mind.

Common soil amendments:

  • compost
  • sand
  • manure
  • lime
  • peat moss

Adding organic materials, such as our Coco-Fiber Potting Medium and compost will improve most every soil type. Organic materials bind sandy soil particles so they retain moisture and nutrients better. They also break apart clay and silt particles, so that water can infiltrate and roots can spread.

Soil Types

  • Clay and silt soils are made of very small particles. They feel slick and sticky when wet. Clay and silt hold moisture well, but resist water infiltration, especially when they are dry. Often puddles form on clay or silt soils, and they easily become compacted.
  • Loam soil is a mix of sand, silt or clay, and organic matter. Loam soils are loose and look rich. When squeezed in your fist, moist loam will form a ball, which crumbles when poked with a finger. Loam soils normally absorb water and store moisture well. Loam soils can be sandy or clay based, and will vary in moisture absorption and retention accordingly.
  • Sandy soils contain large particles that are visible to the unaided eye, and are usually light in color. Sand feels coarse when wet or dry, and will not form a ball when squeezed in your fist. Sandy soils stay loose and allow moisture to penetrate easily, but do not retain it for long-term use.

In This Series

  • Introduction

Getting Started

  • Acclimate
  • Location
  • Planting
  • Soil Preparation

Care & Maintenance

  • Fertilizing
  • Pest & Disease Control
  • Pruning
  • Spraying
  • Watering

Other Topics

  • Harvesting

Limes – Why are there no seeds?

I have wondered for years why lemons have seeds and limes don’t. No one could really give me a good answer until now.

LA times article

by David Karp

Why don’t limes have seeds

If you’d like to read the whole article, just click on the link above. I’m going to paraphrase a bit of it here.

Mr. Karp states that in the last 10 years or so there has been a boom in the quantity and variety of limes and their brethren here in the United States. California, of course is a major producer.

Most of us think of a lime as the big green thing that looks like and is about the same size of a lemon. Those are Persian limes or Tahitian or Bearss varieties and aren’t considered “true” limes. True limes are native to India or Asia and are known in the US as Mexican, Key or West Indian limes. They are distinctive because they are small, round, very acidic with seeds and tend to be more sour than the Persian limes. True limes also will yellow as they ripen in our cool winter climate.

The reason there are no seeds

And now for the reason there are no seeds in our most common, Persian limes. Originally, botanists gave the larger limes like the Persians their own “species” name, C. latifolia. But now, scientists understand that they are a natural hybrid of the true lime. You see, most citrus have two sets of chromosomes, but the large fruited limes have three. The three sets of chromosomes makes them sterile and therefore seedless. Mystery solved.

Options

I for one am very intrigued with the options available to us now. I love lemons and limes. They add just the perfect acid and flavor to drinks and dishes. If you haven’t tried a Meyer Lemon, you are in for a treat. Meyers look like a lemon but taste like a combination of lemon and orange. I grow Meyer Lemons and Persian limes at home in pots and if I can do it anyone can do it. They produce 8 to 15 fruits on each of my 5 plants each year and the blooms smell amazing.

What to look for

Sweet Lime – these are a hybrid of citron and either sweet or sour orange. They are small, round with a prominent nipple. The are yellow when rip and have a pale yellow pulp. They are very low in acid and their flavor is appreciated most by Latin American and Middle Eastern cultures

Kaffir Lime – these limes are related to “true” limes and are best known for the use of their leaves in Thai cooking. The fruit is round with a nob on the top and a bumpy rind. They are bitter and seedy. If harvested at all, the fruit is used in hair wash and insect repellent.

Finger Lime – these bad boys are long and skinny like a finger and grow up to 3 inches long. The skin is thin and the fruit has firm juice vesicles that pop on the tongue like caviar. The flavor is a combination of lime and lemon with herbaceous notes.

Rangpur Lime – these look like a mandarin orange which are medium sized and flattish with seeds. They are orange and are referred to as Mandarin Limes. They are native to India and is actually a hybrid of citron and mandarin. The rind and juice have a clean spicy flavor with is great in cocktails and marmalade.

Conclusions

I’m looking forward to trying some of the different varieties as they become available. If you are a plant enthusiast you should try growing your own limes and lemons. Don’t let them dry out and feed them often and you’ll have fruit the year round. Even though the plant blooms in cooler weather, the fruit will develop slowly and remain on the tree until you are ready for them. Once you have cut into a lime or lemon that you just picked from your own tree and have it be so juicy it squirts you in the eye, you will never go back. – jughandle

Citrus Trees – Care Guide

Light: Citrus plants can cope with our outdoor and glasshouse light levels but should be given a high level of light indoors (either through windows or artificial lighting) being careful not to allow leaf burn in direct summer sun through glass.
When there is no danger of frost, citrus plants like to be outside through the summer months. However, they must be acclimatised gradually to the new light level, by being moved first to a slightly shaded area outside for 2-3 weeks before being put in their sheltered, sunny spot for the summer. Equally, when being brought indoors in winter, they should be kept in the shade for 2-3 weeks before coming inside. This reduces any stress to the leaves that the sudden light change could cause.
Small plants should not be put outside in their first season.
Heat: Citrus trees can tolerate temperatures down to 4°C (even 2°C for short periods) but they must not be frosted. They are also tolerant of high temperatures but prefer to be at neither extreme for too long. Owners are often unaware of just how hot their greenhouse can become on sunny days and of the stress it can cause.
Feeding: During the growing months, the plants should be fed every 2 weeks with a tomato-type fertiliser and given the occasional dose of sequestrated iron (and if possible trace elements) if any yellowing of the leaves occurs. We have a Citrus Feed – summer and winter formula available in our sundries section of the website.
Pests: The most likely pests are woolly aphis and red spider mite. These can be easily controlled with an appropriate off-the-shelf spray. Occasionally scale insect may settle on citrus, and can, again, be easily killed with an appropriate insecticide spray, or by dabbing with methylated spirit.
Water: Water sparingly in winter without letting the pot dry out completely and increase the amount of water once growth starts in the spring. In a hot greenhouse or conservatory the plants will dry out more quickly and may need watering as often as once a day in sunny weather.
Humidity: In hot weather and in central heating, humidity can drop dramatically. If the leaves show signs of stress, the humidity can be raised by a fine spray or standing pots on a tray of wet gravel. Increased humidity will also discourage any red spider mite attack.
Flowers and Fruit: Generally flowering takes place in May but may occur several times in the year in more mature plants. A number of fragrant flowers appear but only about 1% will set (more than this would overload the branches when the fruit reaches full size).
The fruit gradually develops and turns colour around Christmas time. (The colder weather tends to act as a trigger for colouring.) It will then stay on the plants for several months after ripening.

Leaves: Citrus trees are evergreen and will naturally drop an old leaf from time to time. If, however, there is a lot of leaf drop, then the first thing to look at is whether the plant is too dry. This is generally the cause. The second most common reason is poor light, so moving the tree to a lighter position may solve the problem.
Should the leaves drop for any reason, do not be immediately discouraged, as the plant will most likely grow a new crop of beautiful glossy leaves in a month or two, and flower soon after.
Compost: Citrus trees need a slightly acid environment. The pH should be between 6 and 6.5, (Lemons slightly lower pH than Oranges) so use ericaceous compost. Do not use composts containing lime as they will have a higher pH. Most multi-purpose composts also contain lime and have a fairly high pH so should be avoided. Keep the compost open by using an additive mixture such as horticultural grit, sand and grit mixture, or coarse grit. This will improve the drainage and prevent over watering. Do not be tempted to use left over builders sand as this may contain lime.

Pruning: Citrus trees can be pruned to the desired shape and size at any time, however it would be better to prune your tree immediately after fruiting and before the new growth starts to appear. This would then encourage the tree to produce new branches within the area and size you require instead of extending its width and height. With a continuously fruiting variety this may mean sacrificing any blossom or fruit that may be on the tree at the time. January or February would be the preferred time.

There are no special instructions, but the tree will produce a branch from each leaf node so take this into account when cutting back in order to produce a good shape. Cut back to a leaf node that is pointing in the direction you would like to see the new growth take, i.e. pointing upwards and not down, although it is natural for new growth to seek out the light and to grow up rather than down. You do not need to be too particular.

The fruit is produced on old and new wood and even a quite mature, bare branch or trunk can sprout new growth. Take off any shoots that sprout below the graft as you do not want to encourage the root-stock to take over.

Compost for Citrus Trees

lemon tree image by Dennis Carrigan from Fotolia.com

Citrus trees are from the botanical family Rutacae, which originated in tropical and subtropical areas of the globe. They are cultivated throughout the world and come in a great many varieties. Orange, lemon, lime and grapefruit are the most well-known citrus varieties and they can be easily grown in the home garden. Citrus trees need mild winters and lots of sunshine. They grow very well using organic methods of gardening, which include a good composting plan. Compost is nature’s way of creating nutrient rich fertilizer from ordinary plant materials.

Compost Availability

orange tree image by bayu harsa from Fotolia.com

Good organic compost is available commercially at most garden centers and by mail order.You can also make your own compost if you have some backyard space. A backyard compost pile should be 3 feet wide, 3 feet long and 3 feet tall. You can create a simple stacked pile for kitchen scraps and garden waste, you can build a simple bin, or you can purchase a commercial compost maker. Newspapers can also be added to the compost mix in balance with green plant material. They provide carbon nutrients.

Compost Creation

lime? image by tomcat2170 from Fotolia.com

Begin by collecting kitchen scraps and garden plant waste. Compost is basically foolproof but you can tailor recipes to suit your garden needs. Citrus trees do well in a slightly acidic soil. Add coffee grounds to your compost to increase the acid content. Think in terms of “green” and “brown” scraps for a compost recipe balanced in carbon and nitrogen. Vegetable peelings, garden plant cuttings, and brown tree leaves make a good start for a compost pile. The compost pile becomes hot from the combination of moisture, plant material, and air.The heat helps break down the materials in the pile.

Benefits

grapefruit image by Glenn McGloughlin from Fotolia.com

Citrus trees benefit from a planting mixture of compost and garden soil. Composted soil allows the young tree’s growing roots to spread easily because the soil is loose and pliable. The addition of compost will create a nutrient rich growing environment for the young tree. Compost also makes the soil absorb water easily.You may notice that your tree is more resistant to pests and disease problems. Compost creates a slow-release of nutrients so the tree benefits constantly over time.

Expert Insight

Lemon tree image by Timo de Looij from Fotolia.com

The University of Florida Extension School recommends that you begin a fertilizing program one month after the citrus tree is planted. Compost is the best fertilizer to use for many reasons. The tree is able to absorb compost nutrients at its own pace. Chemical fertilizers can burn sensitive root systems by releasing high-nitrogen content into the soil all at one time.Compost creates a constant nutrient recycling process in the tree’s root system. Compost creates a more aerated soil rich in humus which absorbs and retains water more easily. This reduces water consumption and water irrigation bills.

Significance

Orange tree image by nw7.eu from Fotolia.com

A regular composting schedule benefits mature citrus trees by helping them resist disease and pest infestations. Healthy soil makes healthy trees, which resist the onslaught of aphids, whitefly, and leaf diseases. Microorganisms are being constantly recycled throughout the tree’s root system and top growth because of the slow-releasing nutritional benefits of compost.Compost increases the constant availability of minerals into the soil. Compost is less expensive than chemical fertilizers, especially if you make your own.

Citrus Growing Guide

Citrus trees laden with juicy lemons, oranges, limes and mandarins ready to be plucked from the branch are a quintessentially Kiwi addition to many home gardens. Plant in your garden or in pots.

Choose a variety

Before you get started, choose a variety suited to your garden and cooking needs. Below are some popular orange, lime, lemon, mandarin and grapefruit varieties to plant.

Orange: Best Seedless, Harwoods Late, Ruby Blood, Seville.

Lime: Bearss lime, Kaffir lime, Tahitian lime.

Lemon: Eureka, Meyer, Lemonade.

Mandarin: Burgess Scarlet, Clementine, Satsuma.

Grapefruit: Golden Special, Orlando, Wheeny.

Discover top citrus varieties

PREPARE

Choose a suitable spot: citrus trees are frost tender and they do best in a consistently sunny environment with adequate rainfall, in an area sheltered from cold winds.

The better the soil, the better your plants will grow. If you are starting with an existing garden bed dig in organic matter like Tui Sheep Pellets and compost to your soil. Then you can add a layer of Tui Citrus & Fruit Mix. This mix contains potassium, magnesium and iron necessary for flower and fruit development and healthy green growth. SaturAid soil wetter channels water directly to the roots and added seaweed extract stimulates root development whilst improving overall plant health. If planting in pots or containers, plant in Tui Citrus & Fruit Mix.

Clear the area before planting, removing any weeds.

PLANT

Planting citrus in the garden:

  • Soak your tree in a bucket of Tui Organic Seaweed Plant Tonic before planting and allow to drain. This will help prevent transplant shock and give your citrus a healthy start.
  • Add a layer of Tui Citrus & Fruit Mix to the planting area.
  • Dig a hole, approximately twice the depth and width of the root ball of your plant.
  • Gently take the plant from the current container, loosen the root ball and remove any loose or dead plant material and roots.
  • Fill in with Tui Citrus & Fruit Mix. Press mix gently around the base of the plant.
  • It is a good idea to stake when planting, as citrus don’t like having their roots disturbed – this will help support the tree.
  • Water your plant well and continue to water regularly.

Planting citrus in pots and containers:

  • Soak your tree in a bucket of Tui Organic Seaweed Plant Tonic before planting and allow to drain. This will help prevent transplant shock and give your citrus a healthy start.
  • Half fill your container with Tui Citrus & Fruit Mix.
  • Gently take the plant from the current container, loosen the root ball and remove any loose or dead plant material and roots.
  • Position the plant in the centre of the new container and fill with Tui Citrus & Fruit Mix up to 3cm from the top.
  • Gently firm the mix around the base of the plant. The mix should be at the same level on the plant as it was in the previous container.
  • Water your plant well and continue to water regularly.

NOURISH

Replenishing nutrients used by your citrus plants ensures they will grow to their full potential, producing abundant and juicy crops. Feed your citrus in spring and summer to encourage maximum fruiting and flowering.

Citrus require higher levels of potassium and magnesium, and Tui Citrus Food is specially blended with all the nutrients needed for citrus planted in gardens. Feed citrus planted in containers with Tui NovaTec Premium fertiliser.

Magnesium deficiencies can be common in citrus, shown by yellowing leaves. Apply Tui Epsom Salts around the drip line of the tree (where the leaves extend to), to correct the deficiency.

Citrus require more watering over the summer months – and well watered, well nourished citrus will have a better chance of keeping insect pests and diseases at bay.

The weather, weeds, pest insects and diseases can all impact on the success of your citrus. Protect your plants from the elements with layers of mulch, to help keep their roots moist. Keep the area around your citrus weed free.

If you have lemons that are ready to be harvested, try Christine’s Lemon Brownie recipe to enjoy your bumper crop.

Tui Tips

  • Prune if you need to for either a desired shape, to remove any diseased stems, or to improve air circulation. Remember leaves are the life of the tree, so don’t cut unnecessarily, particularly before the tree has matured. If you are pruning, avoid September/October as there is risk of lemon tree borer laying eggs in fresh cuts.
  • In the first year after planting your citrus, remove any fruit that sets. This allows the tree to establish itself and encourages better fruiting in the following seasons.

Citrus trees are trendy. The proliferation of portable trees—grafted onto dwarf rootstock—makes it possible for almost anyone to grow a lemon, lime, or kumquat without having a large space.

With the rise in popularity comes the challenge of citrus care, especially in climates with hard winters, when the subtropical trees must overwinter for months indoors in conditions that can be stressful to the plants (and sometimes to their owners). Indoor winter conditions are challenging, with lower humidity, higher and drier heat, and more difficult watering protocols.

While we feel that we have turned the winter corner and are headed toward spring, this final stretch is a crucial one for overwintered citrus, when problems that have been building up sneakily can threaten the trees we love.

Read on to learn what you might be doing wrong with your overwintered citrus, and how to fix it.

Photography by Marie Viljoen.

1. Poor drainage can kill citrus trees.

Above: The annual citrus migration in my house in Brooklyn (USDA zone 7b) begins when nighttime temperatures begin to dip reliably below 50 degrees Fahrenheit. In October my collection of two sturdy Thai limes (Citrus hystrix, also called makrut), a Meyer lemon, and a petite finger lime (Citrus australasica) is herded indoors for a long winter stay.

Citrus trees require outstanding drainage. Soggy bottoms will kill them Water must flow right through the pot and out. I mix my potting medium with large handfuls of shredded hardwood (I use a natural cedar mulch – meaning no nasty dyes). Softer woods like pine break down too fast. My mix is one-third shredded wood to two- thirds potting medium. My pots have large drainage holes in the bottom. If your pots are set in an ornamental, closed pot, it is imperative that you never allow them to stand in water. If the water stands for more than 12 hours after watering the tree, drain it (see No. 2). More work for you, but essential.

Signs of poor drainage: damp pot bottoms, constantly moist soil, fungus gnats in the room, yellow leaves, drooping leaves, leaf drop.

2. Overwatering can kill citrus trees.

Above: On average my citrus trees spend about seven months inside, going back out in late April. I have learned, sometimes the hard way, how to care for indoor citrus, so that by mid spring they are in excellent health and ready to make a break for the great outdoors.

Citrus hate having wet feet, and overwatering is the most common cause of their poor health. Do water deeply, but only water again when the pot is close to dry. Nancy Lingner, who provides customer support at LemonCitrusTree (her daughter, Crystal Kim, owns the business) recommends that you drench the pot and “drown the soil” allowing the water to run freely from the drainage holes.

To do this, Nancy likes to keep trees on a stand above a substantial plastic saucer that can accommodate one gallon of runoff. Because of space constraints I use shallow pot feet and smaller saucers. If water in the saucers touches the bottom of the pot, I let it remain in the saucer for up to 12 hours (thirsty trees will absorb this water again). But after 12 hours, I suck up excess water with a turkey baster (yes, really).

I also like to use terra cotta pots. If the outside is dark and damp at the base, this is a sign that the soil in the bottom of the pot is too wet (even if the top is dry), which is not good, so I hold off on watering. In terms of touch and feel, the top inch or two of soil will also transition from dark and moist to the touch to lighter and dry. Time to water.

Signs of overwatering: the soil stays moist every day; the bottom of a terra cotta pot looks dark, or green, and is damp to the touch; water stays standing in the saucer; the leaves are drooping, but not dry and crisp; the leaves gradually turn yellow all over and drop; little bugs like fruit flies hover everywhere – these are fungus gnats and are an indication that the pots are staying moist too long.

3. Citrus trees also hate to be too dry.

Above: Less common than overwatering, underwatering tends to happen when you go away for a few days, or simply forget. Citrus trees need deep watering, so a spritz on the surface will not help them.

Nancy reiterates that “a few cups here and a few cups there” are ineffective. Establish a schedule (I water once every seven to ten days, for example), water the citrus trees deeply till water runs from the drainage holes, and observe how fast or slowly the pots dry out.

Signs of under-watering: the soil pulls away from the sides of the pot; when you water, the water sits on top of the soil for a while before draining; water runs quickly through the pot and out; the leaves droop, and turn crisp; branches die.

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