How to grow sweet potatoes in the UK

The delicious sweet potato isn’t a traditional British vegetable crop that our ancestors would have grown. However our changing climate is producing much warmer summers, so lots of gardeners in the UK are growing more exotic crops including sweet potatoes. These frost-tender plants produce nutritious, low-fat tubers and they’re loaded with carotenoids, vitamin C, vitamin A potassium, and fibre. So this is a very healthy crop that’s delicious to eat.

Sweet potatoes are not really potatoes

Despite their name, sweet potatoes are not potatoes at all. They’re climbing members of the Morning Glory family, or the Ipomoea family. For many years they were thought to have originated from tropical regions of South America. However Indiana University in America have found fossil evidence in India that suggests that they are native to Asia and not America. They were originally grown as decorative plants.

The sweet potato is the world's third most important root vegetable, after potato and cassava. They are an important food crop in the southern United States, tropical America and the Caribbean, the warmer islands of the Pacific, Japan, and parts of Russia. These are subtropical areas that don’t suffer from frosts. They thrive in average temperatures of 24C, or 75F, and they also need warm nights.

Growing sweet potatoes in the UK - greenhouse or garden?

It all depends on the weather. Gardeners in warmer, sun-baked areas of the UK may succeed with them outdoors in good summers. Those in cooler areas of the UK will have to grow them in containers in a greenhouse, with a frost-breaking heater, or in polytunnels.

Sweet potato plants must avoid frosts at every stage of their growth cycle. If you’re growing them outdoors don’t put them outside until early June and harvest them before mid-October.

Keep them weed-free, because sweet potatoes don’t like competition.

Starting off sweet potato plants

You can buy sweet potato slips and cutting-raised plants. You will probably have more success with more expensive cutting-raised plants, although they are pricier. 

Growing sweet potatoes from slips

‘Slips’ are long shoots that have been removed from ‘chitted’ sweet potato tubers. These are raised from hardier varieties and not supermarket sweet potatoes.

These long leafy shoots have small roots at the base. Soak the slips in water overnight, to rehydrate them.

Plant them into pots of multipurpose compost, and cover the whole length of the stem right up to the top leaves. You will need deep pots.

Keep them in the warmest place you have. A greenhouse is ideal, or a polytunnel, or under a cloche.

If you’re in a warmer part of Britain, you can grow them in the soil. Warm the ground up by covering the area with black polythene in March. Plant outside in May or early June. Cover with fleece and polythene for the first few weeks because cold nights will check their growth.

Growing sweet potatoes from plants

Seed companies are now selling cutting-raised plants and these give a better yield.

Check the compost is moist and, if required, leave your plants to soak in shallow water for a few minutes until the top of the compost is damp.

Stand the plant in a warm, light, airy place such as a windowsill or conservatory and allow to grow, ensuring that the compost is kept moist.

Once the roots fill the pot and hold the compost together, transfer your plants into their final growing place. It must be warm and sunny.

If you’re growing them in the ground space them 30cm (12in) apart, leaving 75cm (30in) between each row.

Once each plant has reached 60cm (24in) pinch out the tip to encourage more side shoots.

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Harvesting sweet potatoes

The foliage should begin to yellow and die back after 20 - 24 weeks and the crop should be harvested before frost strikes.

Try not to water in the last 3 or 4 weeks of growth, this will discourage the tubers from splitting.

Early October is an ideal time and great care should be taken not to damage the tubers.

Place your freshly-dug, UNWASHED tubers in trays and keep them in a warm area at a temperature between 25-30°C, with high humidity, as this will help to prevent weight loss during curing. They should not be touching each other, so space them out.

Allow your tubers to cure for 7-10 days and then they will store at 10-12°C for up to six months. Alternatively leave them for 21 days at 21C. They should feel moist but firm.

Wrap them in newspaper.

Leave them for another 6 - 8 weeks before eating them, to allow the starches to turn to sugar. Winter squashes also get the same treatment, as do parsnips.

Try one of our many delicious sweet potato recipes, or find out how to cook sweet potatoes

Sweet potato varieties suited to growing in the UK

‘Beauregarde’

The best starting point and the most commonly grown variety in the UK. It produces lots of sweet, orange coloured tubers.

‘Evangeline’

This high-yielding sweet potato produces large, red-skinned tubers with a high-sugar content. Handsome and taller top growth.

‘Bonita’

Consistent, elongated tuber with pink skin, that fades when stored. The pale-yellow flesh has an intense nutty flavour.

‘Erato Orange’

Recommended for growing in large pots during the summer months. The orange flesh has a bright orange-red skin.

‘Erato Gusto’

This produces flavourful, large red-skinned tubers with white flesh. The flavour’s sweeter so it’s very popular.

‘Erato Violet’

Small all-purple tubers with a rich sweet flavour.

Where to buy in the UK

Swiss-based Exotic-specialist Lubera - www.lubera.co.uk is a good supplier of sweet potatoes, but at present UK shipments are on hold due to Brexit until a solution is found. Thompson and Morgan also offer a range of sweet potatoes.

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