Growing lemon trees in pots

Lemon Lemon tree, very pretty and the lemon flower is sweet – but grow it in a pot and be prepared to face defeat! Well that’s my take on the old song, anyway.  And if I had a dollar for every time I’ve been asked “what’s wrong with my lemon tree” then I’d be a rich woman!  The Italians have been successfully growing citrus in pots for centuries but in the tropics and subtropics we rarely get it right.  This is because we’re challenging Nature by trying to grow a plant that thrives in dry climates with low winter rainfall and hot, dry summers.  Luckily most citrus bear fruit in the subtropical autumn/winter when it’s cool and dry but the soggy summers encourage pest and disease problems. So there are three main rules when growing a lemon tree (or any other citrus tree) in a pot:  The right environment, the right watering and fertilising program and the right care regime. ENVIRONMENT Choose a BIG pot that is wider at the top than at the bottom but not so small at the base that it can easily topple.  A lemon tree grows large and bushy and you don’t want to keep repotting so fill up any empty spaces with herbs that can be removed later. Choose a sunny position with plenty of space all around.  Citrus needs at least six hours full sun a day and an airy position discourages fungal diseases.  Perfect drainage is essential so put some gravel or small stones in the bottom of the pot, top with a 5 cm layer of coarse sand then fill the rest with a good quality potting mix. WATER AND FERTILISER Water thoroughly every two days; more in very hot weather.  Check regularly to see that the growing mix is neither soggy nor too dry.  Don’t spray the leaves because this encourages fungal diseases and sooty mould.  The potting mix will feed the plant for the first three months; after that apply a citrus fertiliser according to the instructions on the packet – usually every two months is enough. CARE Top up the potting mix every spring, first removing about one third of the old mix and flushing the rest with a hose at full strength.  Flushing breaks up a mix that is starting to harden and become too impacted around the roots.  It also gets rid of any build up of salts that come with regular fertilising. Lemon trees and other citrus are sadly prone to health problems and attack by insect pests. The leaves should always be a rick, deep green (darker in mandarins) and if they are not then start looking for problems. The most common health problems are due to incorrect nutrition and will show themselves by yellowing leaves or yellowing along the veins only.  If you are applying a complete citrus fertiliser regularly then this should not occur.  However, if older leaves develop yellow veins then dissolve a tablespoon of Epsom Salts in a 5 litre watering can and pour around the roots.  This problem is more common with citrus grown in ground than in pots.  Sooty mould is an unsightly black deposit on leaves and stems caused by the secretions (commonly called “honeydew”) from certain insects such as aphids and scale.  These are often found in association with ants so if you see ants all over the tree, check for their host insects and wash them off with soap and water.  This treatment also gets rid of the mould.  Adding some pesticidal oil such as Neem, or even a teaspoon of household disinfectant, will discourage the problem from re-occurring. The most common insect pests of citrus are Bronze Orange Bugs and Citrus Leaf Miner.  The former reveal themselves through a pungent, unpleasant smell and are either green (when very young) black or bright orange.  They can be picked off by hand but if the tree is badly infested use Pest Oil or Confidor.  If you handle them, they secrete a sticky, smelly liquid which is mildly corrosive.  Their sap sucking habit damages the branches and leaves.  Citrus Leaf Miner is the caterpillar of a moth that lays its eggs in new, tender young leaves.  The caterpillars leave pale, silvery trails through the leaves which become distorted and pallid.  Pest Oil discourages the moth from laying so be alert to the first signs and then spray the new growth and remove any leaves already affected.  This or any other insecticidal oil will kill off most insect pests.  However, it’s always safest to be sure so if your potted lemon tree looks unthrifty, with yellowing or distorted leaves, or blackening tips, get advice either on-line or from your local garden centre. Lemon trees grown in-ground in subtropical climates often show signs of citrus scab which are brownish lumps and patches on the fruit skin.  It looks bad but doesn’t harm the fruit.  However, as lemon trees are grown in pots for ornamental reasons you don’t want scabby, unsightly fruit so spray in mid-spring with a solution of copper oxychloride and white oil (available from nurseries/garden centres or hardware stores).  This stops the problem occurring and you should have lovely yellow unblemished lemons. Potted lemon trees need pruning, unlike those grown in the ground.  Lightly trim to shape as required but if you want flowers and fruit, don’t hard prune when flower buds start to appear.  Water shoots – the long, pale, branchlets with (usually) larger leaves than those on the main branches – grow from the base of the tree, below the graft mark, and should be removed.  If the branches in the centre of the tree are too thick and tangled, gently remove a few to open it up – this helps avoid fungus problems by letting more light into the centre of the canopy.  Always use sharp secateurs or pruning saws, and sterilise them first. After five years or so the constraints of being confined to a pot affect the roots of lemon trees and they begin to fail – symptoms are smaller leaves, leaf drop, fewer fruit or fruit drop.  The whole tree begins to look down at heel.  There are horticultural techniques to de-pot and trim the roots but these require a lot of skill and effort.  The obvious answer is to buy a bigger pot but if this is not feasible then just remove the tree and either plant it outside or just throw it away – you’ll have had plenty of value from it by then and no plant lives forever. Remember, if you want any more advice on this topic or any other, just email me at jrlakemedia@gmail.com and I’ll try to help.

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