Hope for the zest: how to grow citrus plants in cool climates

Italy was described last year by Helena Attlee as “the land where lemons grow” in her excellent book of the same name. I have just been looking for their starter homes in England. Lemons are being grown extremely well in polytunnels in West Sussex.

This non-winter has been tantalisingly kind to their owners. In London, mild weather has let them get away with plant murder — the habit of leaving lemon trees and grapefruits outdoors from November until May. At the Citrus Centre in Pulborough (citruscentre.co.uk) this bad practice is banned. Thousands of citrus trees are wintered in tunnels and kept at a temperature above freezing. They are a splendid sight, rows of well-potted lemons, limes and oranges at heights that would make Mayfair’s gardeners reach for their credit cards. If you want a citrus tree for your conservatory, and in summer for your garden, the centre is the answer.

Its owners, Chris and Amanda Dennis, run a stock of about 15,000 plants, spanning about 130 varieties up to sizes that are impressively mature. They live on the job, do the work personally and cope with their three children on site. They have years of experience in the nursery trade and give off the optimistic calm that always makes me think that if I were a plant, I would do my best for such a person. When they became interested in the citrus and saw a gap in the English market, they studied the plants far and wide and scoured the US for good varieties. On a chilly morning they answered my questions effortlessly and told me which ones to buy and why. They then showed me a fruiting tree of a type that I know as a historian and a reader of the Bible but one I never expected to see in yellow flesh in Sussex.

The charms of the citrus are evident: fresh evergreen leaves, exquisitely scented flowers and a constant sequence of squashable fruit. They grow fast and do not need complicated pruning. To survive and thrive they must be brought under cover in October and kept there until late May. They need a temperature no lower than 3C. They must not be kept too near a radiator, but a bay window or a space by a glass door is fine for them. Small plants can also spend the days on sunny windowsills. They need plenty of light and are ideal in a conservatory. In a greenhouse they drop their leaves if they are heated by temporary oil or paraffin heaters. Electric fan heaters, though, are fine.

They do not like lime-free soil. A pH of about 6 is ideal and the centre suggests a compost of which a quarter should be chopped bark and the rest a coarse commercial mixture with some peat in it. The main reasons for failure are overwatering and insects, especially red spiders. The watering has to be restrained. It is much better to let a plant beg for water than to dampen it regularly. The big mistakes are to stand a potted plant in water and to water it little but often. The advice is to watch the leaves and see when they are looking lacklustre and beginning to turn downwards. The centre’s rule is that for every citrus plant killed by underwatering, 200 are killed by overwatering. Wait for signs of drought and then soak the dried-out pot thoroughly.

Why do the fruits sometimes become soft and apparently rotting? The usual answer is that the plant needs water and is taking it from the fruits, not from the roots. A good soaking will correct it. For heavy crops of well-formed fruit, feeding is essential all year round. The centre sells its own blended feed and strongly recommends it for the purpose. I had not realised how greedy a grapefruit can be.

The menaces to all citrus are not secateurs but red spiders

Pruning is best done in early spring and can be ruthless if your citrus has grown too freely. Plants will shoot again from the pruning-point as readily as a cherry laurel. Do not cut them right down as they have been grafted on their lower stem. The menaces to all citrus are not secateurs but red spiders, those curses of indoor carnations. Outdoors, the plants can be hosed from time to time, but indoors they need to be hand-washed with soapy water, just like the dog. The red spider likes life in a conservatory, but it can be controlled there by biological means. In a drawing room the mite is not usually a problem. The other unwanted visitors are scale insects, which leave a sticky patch on some of the leaves, followed by a sooty mould. It does not hurt the plant, but for appearances it needs to be washed off. If the new young growth becomes twisted, it is being attacked by greenfly. Spray it with an aphid killer.

Otherwise, most citrus are rewardingly easy. Avoid oranges if you are a beginner and, in the centre’s experience, avoid the widely available Meyer’s lemon, a hybrid that has sweet fruits but is not easy to please. Among lemons, go for the reliable Four Seasons and the Spanish staple Verna, which flowers up to three times a year. Try a lime too, Tahiti being the easy one with a good crop of fruit. If you like Thai cooking, the Kaffir lime is the one with the aromatic leaves that Thai recipes specify. The leaves are far more pungent and effective when freshly picked off the plant. Among grapefruits, Amanda gives her top mark to an Australian one called Wheeny. Its name is not the Australian for “tiny”. It arose in Wheeny Creek in New South Wales and is the centre’s top seller.

At the back of the Dennis’s first citrus house, I marvelled at trees with big orange-yellow fruits and a thick skin. I am not alone in marvelling. They are citrons, known in the Middle East long before the citrus, one of whose varieties is the Etrog used in Jewish festivals, including the Feast of Tabernacles. When Alexander the Great conquered the old Persian empire, one of his followers wrote about the methods for cultivation of these citrons at Ecbatana, modern Hamadan, home of the Medes. The bright yellow fruits came over to Greece where they are duly admired by the Athenians’ equivalent of an “Essex girl” in a comedy about Alexander’s time. The silly twit, a Boeotian, thinks they are golden apples from the mythical Hesperides. Wiser than her, I mistook them for a sort of pointed grapefruit.

(Ed’s note: I have been growing citrus for 30 years. Oranges are easy and most of them can take a little frost. One of my miniature orange trees lives outside, in the ground rather than in a pot, in Oxford. My potted citrus comes inside during winter. The majority take very little water while others drink quite staggering quantities. Either way overwatering should never be a major problem if the correct compost is used and the roots are never allowed to stand in water. I’ve never had to wash mine. Feeding is important and, sometimes, I add a dose of sequestrated iron and seaweed as well as a liquid citrus feed.)

Photograph: Natural History Museum, London/ Bridgeman Images