Gardening: There's more to juice than Jaffas

A citrus fruit is an ideal pot plant to cheer you through the winter gloom, especially if it's a Tahiti lime.

Can there be anything more agreeable in Winter," enquired the horticulturist Richard Bradley in 1718, "than to have a view from a Parlour or Study through Ranges of Orange Trees and Curious Plants of Foreign Countries, blossoming and bearing Fruit, when our Gardens without Doors are, as it were, in a State of Death?"

No, Mr Bradley, probably not. It's acquiring that view that is the problem. My study looks straight out on to a border close to a state of death: huge leaves of crambe melting messily round the stump of its crown, peony foliage crusted and brown, the gaunt, twiggy outline of a dark red rose, `Souvenir du Docteur Jamain', mounds of damp leaves blown from the beech tree. Oh for a range of orange trees instead.

An important part of their appeal is that they look their best in the months when the rest of the garden is at its worst.

But I like the fictitious quality of citrus trees, too. Each one looks as though it might have been turned out by a craft workshop. The bright fruit is so perfect and unreal. The colour contrasts so acutely with the sober, handsome foliage.

With the prospect of an orangery (or even a mini lean-to conservatory) as distant as an oasis in the desert, I went instead for my citrus fix to Chris and Amanda Dennis's nursery near Pulborough in West Sussex. It was a horrible, damp, foggy, grey day, but as I walked into the show greenhouse, cruel reality was blocked out by picture-book trees, flowering and fruiting all at the same time. The smell was swoony. I had not realised that the foliage of citrus trees is scented, too. The same essential oils that give a lime its intense, tangy smell are present in the leaves as well as the fruit.

Chris Dennis is in his mid-thirties, and the nursery, only four years old, is a triumph of hope over dreary experience. He was working as a general dogsbody in an architectural and design practice in South Kensington when he decided to throw it all in and indulge his passion for citrus trees instead.

Had he established that there was a market need for these things? No, he said, he hadn't, but he was sure there ought to be. His buoyant optimism infected even his bank manager, and the Dennises, starting from scratch, have already built up a thriving business growing more than 140 different citrus varieties.

His trees hadn't enjoyed the miserable summer, he said. Low levels of light and cool temperatures had slowed down the rate of growth.

At low temperatures, the roots become less efficient at transporting nutrients to the leaves. To a certain extent you can get around that problem by foliar feeding, he explained, but you have to use a feed that is high in nitrogen, with all the right trace elements. He sells a well balanced liquid feed at the nursery, but uses liquid seaweed as an occasional booster. Trees get bored with the same diet all the time.

Fortunately, citrus trees, with their neatly contained rootballs, are well adapted to living in pots. In this country, where they have to be wheeled into frost-free quarters for the winter, that is an advantage. The chief danger with pot-grown plants is over-watering. They'll recover from under-watering, says Mr Dennis. Even if they are so dry that all their leaves drop off, they will probably grow back again, but over-watering is fatal.

He uses a very free-draining compost, with plenty of crushed bark mixed into it to help excess water drain away. Use the fruit as an indicator, he suggests.

Water only when the fruit feel slightly squidgy. If they are hard, resist the temptation - especially in winter, when the rate of growth slows down and trees need less sustenance.

Chris Dennis is in the position of a fond parent, loving all his offspring equally, but, if pressed, he points out useful differences between one member of the citrus family and another. Mandarins (such as the handsome willow-leaf mandarin which I ogled covetously) flower only once a year, so if the plant has a hiccup and drops its flowers, as they sometimes do, you have a long wait before the next show.

Lime trees are in flower by Easter and continue to produce a trickle of flowers all through the summer. They don't fruit as heavily as calamondins, but because of that they grow faster; bearing too much fruit slows a tree down. Lime trees are naturally compact, but other types of citrus may need pinching out or pruning to stop them getting straggly. Pruning can be done at any time of the year.

Trees can be potted on each year. That will make them grow faster than if they are left in the same pots, but, as Mr Dennis points out, they fruit better when they are slightly under-potted. Scale insects, like tiny blobs of dirty tissue stuck to the undersides of the leaves, can be a problem, sucking the sap from leaves. Wipe them off with a damp cloth. If you are happy to use insecticides choose malathion, but remember it kills bees and is dangerous to use near fish in aquariums. You will need to spray at least twice.

The difficulty, wandering through the Dennises' nursery, was to resist the urge to pick the golden fruit. I had to keep my hands firmly stuffed into the pockets of my jacket. The diarist Samuel Pepys was equally tempted.

"Mrs Penn carried us to two gardens at Hackney," he wrote in his diary for 1666. "The gardens are excellent and here I first saw oranges grow, some green, some half, and some a quarter and some full ripe on the same tree... I pulled off a little one by stealth (the man being mighty curious of them) and ate it." Lord Brooks, the owner of the garden, had the last laugh. These were Seville oranges.

The Citrus Centre is at West Mare Lane, Marehill, Pulborough, West Sussex, RH20 2EA (01798 872786) and is open Wed-Sun, 9.30am-5.30pm. Send SAE for a plant list and fact sheet. Plants can be sent mail order (ideal for Christmas presents) as long as there is no frost