Roasted, mashed, baked or fried - Sweet potatoes make a delicious alternative to the humble spud. In recent years their popularity has soared and they are easily found in the supermarket. But supermarket ranges are always limited, and with so many different coloured varieties to choose from, it makes sense to grow your own sweet potatoes.
Sweet potatoes are traditionally grown in warmer climates but don’t be put off. New, hardier cultivars mean that now you can grow sweet potatoes in the UK. Follow our sweet potato growing tips for bumper crops in a cooler climate.
Despite its name the sweet potato is not a potato at all! This tasty root vegetable is a member of the Ipomoea family; the same genus as the popular flowering climber ‘Morning Glory’. You will certainly notice the family resemblance from their pretty trumpet shaped flowers and vigorous spreading growth habit. Sweet potatoes come in a range of colours from orange to purple, and it’s not just the skins that are coloured - the flesh is too, so they look spectacular on the plate! Better still they’re low fat, containing only 90kcal per 100g, and loaded with carotenoids, vitamin C, vitamin A potassium, and fibre. The leaves and tips of young shoots can even be cooked as a spinach substitute. In fact Sweet Potatoes are the healthy-eating superstars of the root vegetable world!
All of our sweet potatoes are all suitable for growing in the UK, although ‘Georgia Jet’ is considered to be particularly reliable. For a brightly coloured skins try ‘T65’ - its red skins contrast nicely with the creamy, white flesh. ‘Beauregard Improved’ is our best selling variety, producing smaller tubers with a lovely salmon-orange flesh. Richly flavoured ‘O Henry’ has a slightly different, bushier habit than other varieties and produces it’s tubers in a cluster which makes for easier harvesting.
Unlike normal potatoes, sweet potatoes are grown from ‘slips’. These are the long shoots that have been removed from ‘chitted’ sweet potato tubers. ‘Slips’ don’t have roots, although sometimes there are signs of small roots beginning to appear. The roots will grow once the ‘slip’ has been planted. Whilst it is possible to grow your own ‘slips’ from supermarket sweet potatoes, most supermarket varieties are not sufficiently hardy to grow well in the UK so crops are likely to be disappointing.
When they arrive the 'Slips' will look withered, but place them in a glass of water overnight and they will quickly recover. The next day you can plant them up individually into small pots of multi-purpose compost. When planting sweet potato slips, it’s important to cover the whole length of the stem, so that it is covered right up to the base of the leaves. Try our ‘Sweet Potato Potting On Kit’ to give them a really good start.
Sweet potato plants are not hardy so you will need to grow them on in warm, frost free conditions for 3 weeks or more until they are established. Warm, humid conditions will quickly encourage the slips to produce roots. Once they are well grown, and all risk of frost has passed, gradually acclimatise sweet potato plants to outdoor conditions prior to transplanting them.
Sweet potatoes can be used soon after harvesting, but they will store well for several months if the skins are cured properly. Lay them out in the sun for a few hours immediately after harvesting and then move them to a warm, humid place for 10 days - a greenhouse is ideal. Once the skins have cured they can be stored in cooler conditions provided that they are kept dry.
Sweet potatoes require high temperatures of 21-26C (70-78F), and their long stems need plenty of space as they have a vigorous growth habit. When growing sweet potatoes in the UK, they are best planted in greenhouse borders, polytunnels or under cloches if you live in a cold area. In milder areas they are well worth trying outdoors, planted through a sheet of black polythene to warm the soil and suppress weed growth. Cover them with fleece or plastic cloches - you’ll be amazed the difference that this will make to the temperature.
Grow sweet potatoes in full sun on fertile, well drained soil. They are not particularly fussy but do prefer an acid or neutral soil. Plant sweet potatoes 30cm (12") apart, leaving 75cm (30") between each row. Where space is limited you can even grow sweet potatoes in containers or patio bags.
Water sweet potato plants regularly. If growing your crop undercover, remember to open doors and windows during the day to keep your greenhouse or polytunnel well ventilated. Greenhouse and container crops will also appreciate a feed of general purpose fertiliser every two or three weeks.
Sweet potatoes have a vigorous growth habit and long sprawling stems. In the greenhouse it may be useful to train the stems onto strings or trellis to keep them tidier. Outdoors you can simply spread the stems out around the plant. Pinch out the growing points of stems that extend beyond 60cm (2’) to encourage more lateral stems to develop.
In late summer, approximately 12 to 16 weeks after planting them, you will notice that the foliage and stems begin to turn yellow and die back. Now is the time to start harvesting your sweet potatoes, although they can be left in the ground longer if you prefer larger tubers. Make sure that you lift them before the first frosts though, to avoid the tubers being damaged by the cold. Lift them with a fork taking care not to bruise them.
Plants and gardens have always been a big part of my life. I can remember helping my Dad to prick out seedlings, even before I could see over the top of the potting bench. As an adult, I trained at Writtle College where I received my degree, BSc. (Hons) Horticulture. After working in a specialist plantsman's nursery, and later, as a consulting arboriculturalist, I joined Thompson & Morgan in 2008. Initially looking after the grounds and coordinating the plant trials, I now support the web team offering horticultural advice online.