Care of Citrus
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Notes on the care of Citrus

Citrus trees make interesting and attractive indoor plants. They provide year-round interest, with fragrant white flowers, followed by small fruits which take 4-6 months to reach full size. The fruits can be picked at any time after ripening, and will retain their flavour on the tree for several months. The miniature-fruited Calamondin tree makes an excellent houseplant for a windowsill; while the larger-fruited varieties are ideal for conservatories and greenhouses, or any light position which has adequate room to accommodate their growth.


All Citrus enjoy high light levels, so smaller plants will do well on a windowsill in the house. Larger plants need a conservatory, greenhouse or sheltered summer garden, but should be given supplementary light if they are to be kept away from windows indoors. Be careful not to allow leaf scorch in direct summer sun through glass. East or West facing windows are best in Summer. Try to keep dark-coloured pots shaded as roots can become overheated and die; water evaporation through unglazed terracotta pots will have a slightly cooling effect.

When there is no danger of frost, Citrus trees like to be outside in 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.


Most Citrus trees can tolerate temperatures down to 4°C (even 2°C for short periods). They must not be frosted, but a cool period is useful over the winter to rest. 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 conservatory can become on sunny days and of the stress this can cause to their plants and trees. A Min/Max thermometer is a ‘must’ for measuring temperatures when no-one is around. Central heating can put the trees under stress in Winter, and ideally they do better in a cool room or conservatory, rather than a warm living room. (See last page for cold hardiness).


Water less often in winter without letting the pot dry out completely, and increase the amount of water once growth starts in the spring. As a general rule, when the top of the compost is beginning to dry out, give enough water to reach the bottom of the pot, preferably washing a little out through the bottom each time. Do not water again until the surface of the compost starts to dry again – this may be every day in Summer, but not for 2 or 3 weeks in cool Winter weather. The big pots take a lot of water, so enough must be given to reach the lower part of the pot (maybe several gallons). Be flexible about watering - judge the need by the look of the compost rather than the day of the week! Over-watering can cause problems too, by drowning the roots and creating stagnant soil conditions which encourage root diseases. With small plants it may be advisable to immerse the whole pot in water to thoroughly soak the compost and allow to drain. Citrus should never sit in water for longer than about an hour.. During colder periods, compost should be kept dryer.


Keep the top feeder roots of the tree covered with compost if possible. Trees should be fed weekly when in growth with a citrus fertiliser (high in trace elements). Use Summer formulation from March to September inclusive, and the Winter formulation fortnightly throughout the rest of the year, or weekly if the plant is growing actively at room temperature. If citrus food is not available, then a seaweed based fertiliser is adequate if supplemented with the occasional dose of sequestrated iron and trace elements when any yellowing of the leaves occurs. Foliar feeding can also be helpful in correcting deficiencies. Too much feed will lead to scorching of the leaf tips, and it is a good idea to wash the compost through with lots of water once in Summer and again in Autumn to avoid a build up of fertiliser salts.


The ideal humidity is about 50%. 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. In centrally heated conditions, a humidifier can be helpful. Increased humidity will also discourage red spider mite attack.

Flowers and Fruit

Generally flowering takes place in May, but may occur several times in the year with fruit setting each time. An enormous number of fragrant flowers appear, but only about 1% will set on the large trees (more than this would overload the branches when the fruit reaches full size). Calamondins and kumquats and some lemons, especially Meyer, set a higher percentage of fruit and may even have to be thinned to avoid weighing the branches down too much. Dry, hot conditions will not favour fruit set, which can be improved by misting the flowers.

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 tree for several months after ripening. Calamondins and Valencia Late Orange trees are noted particularly for holding the ripe fruit on the branches for 6-10 months


Most Citrus trees are self pollinating, with the exception of some Mandarines where cross-pollination with an orange improves the yield.


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 tree is too dry. This is generally the cause, particularly in the lower half of a big pot. The second most common reason is poor light, so moving the tree to a lighter position may solve the problem. Over watering can also cause problems - do not give more water until the surface of the compost is looking dry. Inadequate feeding may also cause leaf drop: this can be rectified particularly effectively with special citrus food.

Should the leaves drop for any reason, do not be immediately discouraged, as the tree will most likely grow a new crop of beautiful glossy leaves in a month or two, and flower soon after. Often heavy flowering and new leaf growth trigger some leaf drop in Spring. This is quite normal and new leaves will fill gaps; but more diligent feeding may avoid this leaf drop in the first place.


To keep the trees in shape, pinch out the growing tip once a new branch is 10-15cm (4-6”) long. Regular pinching out of branches will encourage bushy growth nearer the middle of the tree, and this can be carried out at any time of year. Pruning of large branches is best done in February, just before growth starts speeding up, bearing in mind that Citrus trees store excess food in their leaves, so removing too much leaf may result in a poor fruit crop.


In general it is best to repot just before or during the growing months, rather than in the Autumn or Winter. Either loam or peat-based composts can be used, mixed with extra sand or grit to improve drainage, and preferably crocks in the bottom of the pot. The ideal pH is 5-5.5, so a slightly acid (ericaceous) compost is beneficial. Loam based composts will give welcome increased stability for a tree outside, but it will also make large trees extremely heavy to move in and out of doors with the change of seasons. Where possible, pot up one size each time, with enough depth to cover the top feeder roots and give a 1" ‘reservoir’ for water. In normal conservatory conditions, where the size of tree is to be restricted, a final pot size of 45cm will be adequate. Once it has reached this size pot, instead of repotting into a larger size, take the rootball out of the pot at the end of February: if it is overcrowded with roots, cut off about 2.5-5cm (1"-2") all around the edges, and put back into the same pot with fresh compost around the edges; or, if this has been done before with the same tree, remove 3 vertical triangles of compost from the rootball, and refill gaps. Try and roughly match the original compost, i.e. use a loam-based compost, if that has been used before. Keep the tree fairly cool and shaded for the following month, in order not to make great demand on the root system until it has started re-growing.

Varieties in order of Cold Hardiness

Most tender:
  • (Min.6°C):
    • Citron
    • Lime
  • (Min. 4°C):
    • Lemon (other than Meyer)
    • Grapefruit
    • Orange
    • Mandarine/Clementine
    • Calamondin (Citrofortunella microcarpa)
    • Satsuma
    • Kumquat ‘Fukushu’
Most cold tolerant:
  • (Min. 2°C):
    • Kumquat ‘Nagami’
    • Meyer Lemon


The most likely pests are aphids (greenfly), red spider mite and mealybug. These can be 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. As dead scale insect can harbour viable eggs under it, any scales are best removed by rubbing or scraping gently with a fingernail.

A systemic insecticide can be used to very good effect, but should be used with caution when there is any intention of eating the fruit within 2-3 weeks. (See insecticide bottle for details about use on vegetables and fruit). Sprays containing Dimethoate may cause some leaf fall in Citrus, but this is not usually too serious. Never spray a plant in full sun outside or under cover; it is best to spray either very early in the morning or in the late afternoon/evening as otherwise the leaves may become scorched.

Biological control

Insects are the easiest and cleanest methods of keeping pests down in the whole conservatory, but should not be introduced for 6 weeks after any chemical sprays have been used. In these 6 weeks, a fatty acid (insecticidal soap) spray may be used, as it is best to reduce pest populations as much as possible before bringing in any beneficial insects. Average temperatures of above 20°C are necessary for most biological control agents, so they are used only between April and September, unless high levels of heat and light can be provided at other times.


  • Red Spider Mites: Phytosieulus persimilis
  • Whitefly: Encarsia formosa
  • Thrips: Amblyseius cucumeris
  • Aphids: Aphidius
  • Mealybug: Cryptolaemus montrouzieri
  • Vine Weevil: Hortinem (Nematodes)
  • Caterpillar: Bacillus thuringiensis (Bacterial powder for spraying)
  • Scale Insect: Metaphycus helvolus
For more information please contact our Helpline at 01206 240466.

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