Most vegetable gardeners lucky enough to have the use of a greenhouse use it for raising seeds early in the year, extending the season into the autumn, and of course growing tomatoes and cucumbers in the height of the summer. If you’d like to find something a little more exciting when you open the greenhouse door, these unusual crops will appreciate the extra heat.
Melons, Cucumis melo
Difficult to grow outside in the UK, melons enjoy the heat and humidity of the greenhouse. They are grown in the same way as cucumbers, trailing, or climbing up nets, and are best planted on a mound, as they don’t like getting their stems wet. You’ll need to prune them to encourage a good crop of fruit (start by pinching out the growing tip to make the plant bushy, then restrict the plant to four lateral stems and pinch out their growing tips when they have six leaves. Plants fruit on sub-laterals formed on these lateral stems). You’ll also need to feed your plants and keep them very well-watered once they start to flower and fruit.
You can also grow your own watermelons (Citrullus lanatus), for which seeds are sown indoors in April or May, although it’s best to choose an early variety that has been bred to crop well in the UK climate. You could be harvesting fruits weighing five kilos from midsummer, but they will need plenty of water! Like squash, watermelons have male and female flowers, and will benefit from a little help in the form of manual pollination. Prune in the same way as melons.
Peppers, Capsicum species.
It is perfectly possible to grow peppers (both sweet and chilli) outside in a sunny spot on the patio, or on a windowsill indoors. But they also make a great greenhouse crop, enjoying the extra light and heat. They’re treated in much the same way as tomatoes, and seeds have to be sown in late winter or early spring to get a head-start on the season, but you’ll still be able to buy plants at your local garden centre, and there’s a large range of varieties available mail order.
Peppers need to be given a high potash tomato feed every week once they start to flower and form fruits. And, like tomatoes, they need to be kept consistently damp to perform at their best. The ‘heat’ of a chilli depends on a number of factors, including the variety you choose and the weather – so in the event that we have a long, hot summer, handle with caution!
Most peppers grown in the UK are Capsicum annum species, but if you can take the heat and don’t mind a bit of hunting around you can often find seeds and plants for some of the less well-known species, including Rocotos (or Lotocos), which are C. pubescens and have lovely purple flowers.
Lab lab (or hyacinth) beans, Dolichos lablab or Lablab purpureus
Although relatively unknown in the UK, lab lab beans are an Asian favourite. They need protection to grow well in the UK, but if you have a polytunnel or a greenhouse then they can be grown in the same way as climbing French beans, with pods picked as soon as they are large enough to eat. As an added bonus, they have scented flowers that appear from July onwards from seeds sown in April.
Like French beans, lab lab beans are very varied – they come with different colours of both pods and flowers. Some are day length sensitive and will only crop well in the tropics, but there are also day neutral varieties that don’t mind our long summer days.
Dudi (also known as calabash, or the bottle gourd), Lagenaria sicceria
Dudi will grow outside in a good summer, but is more reliable in the greenhouse. It’s a popular Indian vegetable, a bit like a climbing courgette, and the fruits are best eaten when they are young. Like pumpkins, dudi seeds are sown in April or May and potted up into relatively rich soil. They make big plants, so give them plenty of space and a solid support to scramble up. If you do grow them, remember to pop out to the greenhouse in the evening so enjoy the flowers, which open at night!
Sweet potatoes, Ipomea batatas
Sweet potatoes have actually been grown in the UK for over 450 years, but they often don’t crop well outdoors in a British summer. Another big plant, they trail rather than climb, and need to be given a reasonable amount of space. They are grown from ‘slips’ which are cuttings taken from a seed potato, and sold in late spring. Slips need to be potted up and kept warm, before planting out into the greenhouse once they have established a good set of roots – plant them really deeply to encourage tuber production. They like the heat and humidity of the greenhouse and a rich soil, but don’t feed them too much nitrogen as that encourages leafy growth at the expense of the tubers.
Melons and watermelons, all kinds of peppers, and sweet potatoes are all widely available from the major seed companies and garden centres. For anything more exotic try the Sowing New Seeds Project varieties available through the Heritage Seed Library, or a commercial supplier like Jungle Seeds.