With the temperatures we have experienced this year, you may have been tempted to buy a citrus tree which has grown happily in a pot outdoors. However, as the temperatures are falling, now is the time for you to prepare your citrus tree for the colder months ahead.
In October, we can get rain so, if the temperatures remain mild, to prevent your citrus trees becoming waterlogged, consider moving your tree(s) up against the side of the house (so that they are in a rain shadow) or under a porch to prevent the worst of the rain saturating the roots. If temperatures fall dramatically, your citrus needs to be moved undercover; into a greenhouse, conservatory or even in front of a big window in your house. It is important, however, that the plant is kept free from draughts, kept away from radiators (don’t forget underfloor heating), and where the temperature is reasonably constant, not falling below 5oC. It is also important that the tree’s leaves enjoy as much sunlight as possible.
During the colder, darker months, citrus trees’ metabolism slows down dramatically so instead of watering daily as you do in summer, only water when the top half of the soil in the pot has dried out. Using tepid, preferably rainwater, you may only need to water the trees every two to three weeks. When watering, ensure the pots are raised off the ground to improve drainage. Water heavily from the top of the pot and let excess water drain away as citrus trees do not like sitting in water.
Citrus trees have three main categories for hardiness which will affect the winter protection your plant requires:
- Sweet Oranges, Kumquats, Calamondin Oranges, Tahiti Limes, Grapefruit and Mandarins need to be kept at a minimum of 5oC so you will need to wait until temperatures rise again in spring before they go back outdoors.
- Lemons, Chinotto oranges and Kaffir Limes tolerate as low as -2oC for short periods. They will not handle hard frosts, and it is the rootball which will require most protection against freezing, not the leaves. It is worth wrapping the pot in hessian or horticultural fleece even when you bring the plant into shelter.
- Less common varieties incluidng Yuzus and Finger Limes are able to withstand temperatures as low as -15oC but they must not become waterlogged.
Most citrus will overwinter very well – even in quite warm houses – but our dark, wet winter days can lead citrus trees to drop their leaves even if you are watering correctly. Kaffir Limes, Kumquats and some Lime trees seem most susceptible to this, but once the days start to get longer they will pick up and put on new growth. Once they are back outdoors, they will be fine.
Citrus trees are not deciduous, so if your citrus tree is experiencing significant leaf drop this could be caused by sudden or dramatic temperature fluctuations or by being placed in a draughty position: losing leaves is a sign of stress. The early part of the year, when the days are cold and dark, are the hardest months for citrus trees. Misting their foliage, both summer and winter, is hugely beneficial. Misting a few times a week or running a humidifier prevents the leaves from drying out and helps avoid issues like leaf drop or pest infestations. It is also worth putting your citrus tree on a tray of pebbles to provide passive humidity as water evaporates and helps prevent the plants roots sitting directly in water.
It is important that you establish a feeding programme for your citrus trees as they require both a balanced summer and winter Citrus Feed. The summer feed with its high nitrogen content promotes foliage growth, whereas the winter feed which contains potassium and phosphate is essential for fruit development. The winter feed should be given every other watering.
Like all plants, citrus trees can be susceptible to pests, so it is important you keep a watchful eye for them. When your citrus plants are outdoors, birds and other insects along with better air circulation will keep pests at bay. However once indoors look out for scale, mealy-bug, red spider mites, aphids and caterpillars. If your plant develops red brown circles, shows white sticky fluff, webbing, or holes in the leaves these are all signs of pest attack and must be treated as soon as possible. If the problem is not too advanced, spray the leaves a few times each week, morning or evening, with a simple solution of soapy washing up liquid.
During the winter, citrus often suffer from iron or magnesium deficiency, recognisable by the appearance of yellow leaves with dark green veins. Treat this by applying a chelated iron plant drench or a specialist winter citrus feed trace-element spray.
When it comes to repotting citrus plants, most can remain in their original pot for a few years. However, you may wish to move the plant into a different type of container. It is important that you select something of a similar size and avoid disturbing the plants roots as much as possible. Your container should only be slightly larger than the rootball.
Using the right type of free-draining, slightly acidic soil is important. To mix your own use 50% multi-purpose, 25% ericaceous (acid) soil and 25% horticultural grit or sharp sand. Alternatively, buy a ready-mixed Mediterranean & Citrus Potting Compost.
In between repotting, you need to top-dress your plants. Simply remove the top layer of compost and replace with fresh. Repotting is best undertaken in spring or early summer before active growth commences.
