Citrus: Greenhouse Plants
C – cool, minimum of 7°C (45°F) / W – warm, minimum of 13°C (55°F)
These are great fun to grow because of the possibility of their bearing fruit as well as scented flowers and the lovely citrus smell from their glossy leaves and bark. Most Citrus can virtually tolerate frost free conditions but will not do very well and are unlikely to bear fruit. A temperature of 10°C (50°F) in winter is preferable. Fluctuations in temperature should be avoided. The biggest problem is their liability to be attacked by mealy bug or scale insects. Either will secrete sticky honeydew which falls on to the leaf surfaces which then become covered with sooty mould growing on the honeydew. Having controlled the pests, the only way to be rid of the mould is to wipe it away. With large plants when this is not feasible I usually resort to pruning the plant back hard to get rid of most of the foliage. Fortunately Citrus respond well to this hard pruning. Do not be afraid to cut back to quite old wood, cutting always above a node. Within a short time fresh green shoots will appear in such a profusion that it is often wise to thin them out in order to get a well-balanced plant. It will probably take at least one year for flowers to appear. Citrus are heavy feeders and will quickly become yellow-leaved and sorry looking if this is neglected.
Citrus limon, the lemon, flowers in spring. As the fruits take about a year to form and ripen they can be ready for Shrove Tuesday. C. mitis is the Calamondin orange from the Philippines. It is a small compact shrubby plant which is excellent for pots, flowering and producing its small fruits all year round. C. sinensis, of Chinese origin is the sweet Orange of commerce but makes a rather large plant. Propagation can be by sowing the pips. I plant mine just under the surface of theand place them in a temperature of 21°C (70°F). Germination should take place within two weeks but can take up to one month. Interestingly there are often three from one pip. Two arise from embryonic tissue in the mother plant and will be identical to it, whereas one will be the true hybrid and is an unknown quantity. Cuttings of 8-10-cm (3-4-in) long semi ripe wood should be taken during the summer. Lemon and Citron (C. medica) are relatively easy to root in comparison to Grapefruit (Citrus paradisi) and Orange. For the adventurous it is possible to bud any Citrus, usually on to one year old seedling stocks of a close relative, Poncirus trifoliata. This should take place in August. Grafting is also possible. Budded plants usually fruit earlier.