How to grow sweet potatoes in the UK
All you need to know about growing sweet potatoes in UK, in our Grow Guide.
Sweet potatoes are an increasingly popular vegetable crop to grow in the UK, both as an alternative to regular (white) potatoes and in their own right. They are not related to regular potatoes, but are actually a member of the morning glory family (Convolvulaceae). They are vigorous climbing plants with vines reaching 1.5m in length and red, white or purple potato-like tubers. Sweet potatoes are sweet to taste, rich in vitamins C and A, and packed with carotenoids, potassium and fibre. They can be boiled, roasted or made into chips, and the shoots and leaves can be eaten like spinach.
The heart-shaped, fresh green and lush foliage is highly ornamental, making sweet potatoes an excellent crop to grow in a more ornamental garden, or a conservatory.
Where to grow sweet potatoes
Sweet potatoes do best in a warm environment, typically at temperatures of 21–26°C (70–80°F), so in the UK are ideal for growing in a greenhouse, either in large pots or the greenhouse border. You can grow them outside but the crop will be smaller than if grown with protection. The trailing stems can be trained up an obelisk or wigwam of bamboo canes to save space.
You can grow the plants outdoors, especially in warmer regions. Again, choose a sunny, sheltered spot and pre-warm the soil with black polythene. Then simply cut a hole in the polythene to plant the potato, and so it keeps the soil warm to increase your chances of a good crop.
How to plant sweet potatoes
Sweet potatoes are usually grown from slips. These are unrooted cuttings from existing plants and are available to buy via mail order from April onwards. When they arrive, pop them in a jar of water for a couple of days to perk up, and then pot them up into small pots of moist, peat-free, multi-purpose compost, burying as much of the stem as possible, to encourage plenty of roots to develop. Cover the pots with a clear plastic bag or place them in an unheated propagator until they root and show signs of growth.
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Growing sweet potatoes outside
Prepare the ground by removing weeds and adding organic matter, such as garden compost or well-rotted horse manure. Then cover the area with black polythene to warm the soil and suppress weeds – the earlier you do this the warmer the soil will be. Once all danger of frost has passed, harden off the plants by gradually acclimatising them to outdoor conditions, and then cut holes in the plastic about 30cm apart, and plant one sweet potato plant in each.
To aid temperatures further, use a cloche to cover the plants as they establish.
Growing sweet potatoes undercover
Sweet potatoes do best when grown undercover such as in a greenhouse, polytunnel or conservatory. Plant them in the greenhouse border in well-prepared soil, spacing the plants 30cm apart (there's no need to warm the soil with polythene as you would if growing outside).
You can also plant them in large containers filled with peat-free multi-purpose compost enhanced with well-rotted manure or compost. Plant them 30cm apart, with a minimum pot diameter of 30cm (plant one plant per pot if using 30cm pots).
How to care for sweet potatoes
Water your plants regularly and feed with a high potash liquid feed, such as tomato food, every fortnight.
Pinch out the growing tips of longer stems to encourage bushy growth, and tie them into their support.
How to harvest sweet potatoes
Sweet potatoes are ready to harvest when the leaves turn yellow and die back – around 12 to 16 weeks after planting. Make sure you harvest them before the first frosts in autumn, which can damage the tubers.
Use a garden fork or spade to gently lift the tubers out of the soil.
They are best used immediately, but they can be 'cured' to store for a few weeks after harvesting. To cure the skins, lay them out in the sun for a few hours after harvesting and then move them to a warm humid place – such as a greenhouse – for around 10 days. Once you have cured the skins, you can store them in a cupboard or shed for a few weeks. keep them dry and check them regularly for signs of rotting. Avoid storing any damaged tubers as they can rot and spoil the rest of the crop.
Looking for inspiration on how to use your crop? Our friends at olive have curated a delicious collection of sweet potato recipes, including baked sweet potatoes with gruyère, cheddar and rosemary.
How to propagate sweet potatoes
You can propagate sweet potatoes by taking cuttings from plants in summer – simply root them in water, pot them up and overwinter them in a frost-free spot, ready to plant out the following spring.
You can also make your own sweet potato slips, by chitting a sweet potato to produce shoots. You can do this with a shop-bought tubers, but bear in mind that these are not bred to grow in the UK climate and may therefore not grow as well as varieties bought to grow in colder climates. These tubers may also be treated with an anti-sprouting agent, so give them a good scrub to remove it. Then place the tubers in moist vermiculite, perlite or sand in a warm propagator or airing cupboard to encourage sprouting. Slice off the shoots when they are 5-7cm (2–3in) long. Pop them into small pots filled with moist peat-free cuttings compost immediately, and keep them in a warm propagator to root.
Growing sweet potatoes: common problems
Mottled leaves covered in webbing are signs of red spider mite. Increase humidity in the greenhouse to stop them from breeding.
Advice on buying sweet potatoes
- Sweet potatoes do best in a greenhouse or other form of cover, so make sure you have the right growing conditions for them before you buy
- They are only available online; make sure you open the packet they arrive in as soon as they are delivered, as you will need to put the slips in water to hydrate them before planting up
- Some online suppliers sell sweet potatoes as jumbo plugs, which can be planted straight away. These are more expensive to buy than slips but you may have more success with them
Where to buy sweet potatoes
Varieties of sweet potato to grow
'Beauregard Improved' – orange flesh with a sweet flavour
'Bonita' – pinkish tubers with orange flesh
'Evangeline' – orange-fleshed tubers which are almost twice as sweet as many other varieties, but it needs a long hot summer to grow well. Very vigorous.
'Kaukura' – light orange skin and flesh.
'Tahiti' – purple-skinned, white-fleshed tubers.