Tropical & tender crops, for indoors and out

Over the years I have tried to grow almost every edible plant and crop and sometimes been surprised by outstanding successes. To some it may seem unlikely that we could cultivate any tropical plants here in the cold climate of Britain but of course with glass or plastic protection and additional heat we can grow almost anything; I've even produced respectable crops of bananas and pineapples.

However at first glance it hardly seems sensible to suggest that others do the same. Yet most of us already grow many South American natives. We have learnt to cultivate potatoes, maize, French and runner beans, all of which come from the hot New World. We have learnt to look after them and improved their varieties to the point where they've become widely cultivated without a thought as to their origin. The same goes for courgettes and cucumbers; few subjects are more tender yet many of us grow them. And in the flower garden of course there are a multitude of examples of plants from tropical and subtropical regions.

Probably the commonest tender crop we grow is tomatoes - Tomatoes are not an easy crop, their seed from dropped fruits germinates outdoors here but too late to ripen their fruits before the frosts return. So we have learnt to start tomatoes in the warm and plant them under glass or outdoors once the weather has warmed up sufficiently for them to survive. Doing this gives them a head start and they are growing long enough to ripen a few trusses. Given enough warmth and light tomato plants may ramble for yards and produce dozens of trusses though it is a rare year when they manage to ripen more than a half dozen. So we have learnt to de-shoot and de-truss them to concentrate their energy on ripening just the first few trusses for us. Under cover tomatoes have long been dependable and with some considerable help from the plant breeders we now have varieties of tomato that crop outdoors reliably most summers. And although the crops indoors are bigger they never taste so good as the same sorts grown in the open air.

Many of the other tropical and subtropical crops are not much more difficult or demanding than tomatoes. So if you already grow tomatoes successfully then maybe you should try tomatillos. Tomatillos and Cape gooseberries are Physalis and look and grow much like tomatoes with a papery husk, the former are sweet and eaten for dessert, the latter are essential for the authentic flavour of salsa dishes. Tomatillos are grown just like tomatoes and crop prolificly. Cape gooseberries can be grown like tomatoes and are perfectly happy in pots outdoors all summer but crop late and poorly from plants started that spring and do much better from plants rooted in autumn and over wintered just as Pelargoniums and Fuchsias are often treated.

Again if you succeed with tomatoes then try Sweet peppers. These are easy under cover and given a warm spot modern varieties crop outdoors, the hot Chilli peppers seem to need no warmer conditions and surprisingly their crop is just as hot as if grown in the tropics. However yields outdoors are a fraction of those under cover. Both sorts of pepper are happy to grow in big pots and so they can be kept under cover and then go out in mid summer which suits them better than the close atmosphere of a congested greenhouse. Neither sort of pepper needs hand pollination or training though some support is needed for the crop or the weight may snap a stem. They do get aphid attacks but otherwise have few problems.

Aubergines require more warmth - I have not yet raised a decent crop outdoors. Grown similarly to tomatoes and peppers they seem to prefer the bright conditions under glass to the diffuse light under plastic. Aubergines need a richer soil than peppers and their heavy crop needs good support. No hand pollination or pruning is needed but watch out for red spider mite attacks.

Needing even more warmth is Okra. This just does not grow without warm conditions and a rich soil, given them it thrives. Unfortunately the plants only crop one or two fruits at a time so you need several plants to give enough for a meal. I have found the only way to get good yields is to grow Okra on top of a small compost heap made under cover, it never thrives in the cold border soil.

For the best melons and fine cucumbers under cover it is also effective to grow them on small hotbeds or compost heaps. If they are grown in the cold soil of the borders at ground level the crops are smaller, and later. It is essential to give them a very well enriched soil, I find mixing grass clippings in their compost helps and they need plentiful lime as well. Melons are sweetest when they get full sun so theoretically they do well under glass but in practice they prefer the moister conditions under plastic and gladly suffer the diffuse light. It is not essential to hand pollinate melons, or to reduce the shoots and fruits to four as left to themselves they tend to produce one huge fruit and a couple of small ones later; this suits me as I'm not after marketable fruit but gourmet ones! I've succeeded with melons outdoors both under plastic sheets and by starting them off in coldframes and letting them run free as they outgrow it. But to get sizeable fruits the site needs to be grossly enriched and preferably be on an actual hotbed or compost heap. Unfortunately, as yet, the varieties recommended for outdoor cultivation are poor by comparison with old varieties intended for greenhouse culture though hopefully breeders are working on this. On the other hand breeders have worked wonders with cucumbers; these are so much more productive, disease resistant and cold tolerant that modern indoor varieties are in a different league to the traditional and the cucumbers for outdoor cropping are nearly as much improved

So just because a plant is tender does not mean we can't grow it outdoors. Indeed indoors the high temperatures make courgettes have too many male flowers so they are better off outdoors. Likewise such as the ridge cucumber, squashes and marrows are also so quick to grow and crop that they can be sown in situ in May under a plastic bottle cloche, will grow, mature and finish cropping by autumn. Hopefully soon we will be able to do likewise with watermelons, currently these are not easy even under cover and they are very difficult to crop outdoors. Watermelons need less rich conditions than melons and prefer a sandy soil, they are extremely prone to red spider mite. I find the best way to succeed with them is on hotbeds made under plastic or in dead deep freezer coldframes.

Ginger is a tropical crop that we can easily succeed with. Small buds of root ginger potted up in the warmth in spring will produce several pounds of ginger by the autumn. Ginger needs a warm well drained soil with it's leaves in bright shade (sic); in full sun they bleach and in full shade it's too cool. Because of this ginger does best growing in a black pot in the sun but with it's foliage shaded by a taller plant. The plants can go on the patio for the summer. When the foliage dies back in autumn the roots can be dried for winter use, or alternatively the stem bases can be candied earlier in the year.

Lemon grass is an expensive herb to buy yet almost any fresh bit will root and it can be rooted in a glass of water on a sunny windowsill. Ideal for a frost free greenhouse it soon gets big and forms big clumps like pampas grass if given the room. I plant it out for the summer and it survives right up till the hardest frosts when I rescue offsets to grow on. In the same way I grow sugar cane; this is almost the same in habit but huge. Planting out autumn rooted plants in late spring they soon establish and are towering over your head by autumn. Sadly the canes do not get as sweet as in the tropics.

Luckily sweet potatoes do get as sweet, and they give better crops than Irish potatoes. I find they do best in large black pots as this gives higher soil temperatures than in the border. I also find that if the runners are allowed to root they waste energy. It is better to train the runners up a line or stake and then they also get more sun. It is hard to get a sweet potato to sprout but with heat they usually eventually do. These sprouts are best detached from the parent and potted up separately. Likewise in autumn the runners are layered to give fresh plants to over winter which saves sprouting a new tuber and gives bigger plants sooner. I find sweet potatoes need a lot of water, rarely suffer much from pests and some sorts flower very prettily. They can go outdoors all summer if in a warm sheltered spot,

Another tropical root crop is Eddoes, a form of Colocasia. The edible tubers, which have an irritant skin, are sold in supermarkets. Potted up these produce a gorgeous house plant, and given a big pot or planted out all summer they multiply giving a cluster of new tubers. Eddoes make a very architectural addition to any border or they can be stood on the patio in pots.

I've found it's possible to crop sweet peppers, hot peppers, cape gooseberries and even melons on the vegetable beds, I've done so. But don't get me wrong; they have always done much much better under cover. The point is that these and other crops once thought tricky are now easy under cover and marginal outdoors but with climate warming, continued breeding and good techniques outdoor cropping is becoming more feasible. However only in sheltered gardens is it currently really worth the risk of trying these crops outdoors. Still they are possible; that's the marvellous thing about gardening, you can grow anything you want if you try!