Sweet potatoes are tropical climbing plants grown for their edible tubers. Planted as
Sweet potatoes produce trailing or climbing stems that easily reach 1.5m (5ft) or more long. These can be grown vertically up a trellis or wigwam of canes to save ground space, or can be allowed to sprawl.
Unlike traditional potatoes, which are grown from tubers, sweet potatoes are started from cuttings (known as slips) in spring. These must be kept indoors in the warm to get well established, then can be moved to their final growing position in late May or early June, once there is no risk of frost.
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There are several varieties of sweet potato to choose from, producing tubers of various shapes, sizes, levels of sweetness and colours, including orange, purple, red and white. Make sure you buy a variety suitable for growing in the UK, and if you’ll be growing them outdoors, select one of the hardiest options, such as ‘Beauregard’.
What and where to buy
Sweet potato cuttings (known as slips) and plug plants (rooted cuttings) are available from late April onwards from online veg plant suppliers. Young plants may occasionally be available in garden centres.
Sweet potatoes are grown from cuttings in spring, rather than from seed. You can buy cuttings from online suppliers or grow them yourself from shop-bought tubers.
Planting cuttings and plug plants
Both unrooted cuttings (known as slips) and rooted cuttings (plug plants) are easy to grow if kept warm, in good light and watered regularly.
When your cuttings or plug plants are delivered, plant them immediately into small pots of multi-purpose compost. Keep the compost moist, using tepid water. Put in an unheated propagator or cover the pots with a clear plastic bag on a warm windowsill. The cuttings should root quickly and easily.
Move the young plants into slightly larger pots as they grow. Keep them indoors until after the last frost.
You can take your own cuttings from shop-bought sweet potatoes, but bear in mind that these may be less hardy varieties, so not necessarily ideal for the UK climate. Also, the tubers are often treated with an anti-sprouting agent, so choose organic or scrub them clean.
Alternatively, you can take cuttings from tubers you grew the previous year, if you manage to store them successfully until spring.
To grow your own cuttings:
In spring, place sweet potato tubers in moist vermiculite, perlite or sand in a warm propagator or airing cupboard to encourage sprouting.
Once the leafy shoots are 5–7.5cm (2–3in) long, cut them off at the base with a sharp knife.
Insert the cuttings into small pots filled with multi-purpose or cuttings compost, then place in a warm propagator to root (see Planting cuttings, above).
Planting in final position
Once all danger of frost has passed, harden off the young plants by gradually acclimatising them to outdoor conditions.
You can plant them in a large container, growing bag or in the ground.
To plant in a container, choose a pot at least 30cm (1ft) wide and fill with multi-purpose compost, then position one young plant in the centre. Plant at the same depth it was previously growing, firm in and water well. Alternatively, plant one in a growing bag. Then keep in a greenhouse or in a warm, sunny, sheltered spot outdoors.
To plant in the ground, choose a very warm, sheltered location in full sun, with moisture-retentive, free-draining soil. Prepare the site in advance, in late March or April, by forking in lots of garden compost or well-rotted manure, then cover the soil with black polythene, cloches or fleece to warm the soil.
Plant through the polythene, making a slit for each plant at least 30cm (1ft) apart. Water in well, then cover the plants with cloches or fleece – the temperature lift makes all the difference. Provide supports for them to climb up (such as a wigwam of bamboo canes) if ground space is limited.
Sweet potatoes are thirsty plants, so keep them well watered at all times. If plants go short of water, the tubers won’t swell.
When growing outdoors, cover the ground with black polythene before planting, to warm the soil. Leave it in place for the whole growing season, to keep weeds at bay and hold moisture in the soil.
Alternatively, cover the soil with a thick layer of well-rotted manure or garden compost, which will do a similar job.
Feed sweet potato plants in containers every other week throughout the summer using a high potassium liquid feed.
Keep young plants weed-free, to reduce competition for light, water and nutrients. Once established, sweet potato vines grow vigorously and should shade out most weeds.
Harvest sweet potato tubers after four to five months, once the leaves turn yellow and die back in late summer and autumn, before any frosts.
Lift them carefully to avoid bruising the fresh tubers, which have delicate skin. Any damaged tubers should be used straight away. The skins can be dried by leaving them in warm sunshine for a few days.
Sweet potatoes are rich in fibre, vitamins and other nutrients. They can be boiled, roasted or made into chips. They are best used fresh, as they can be hard to store successfully. They freeze well if blanched or boiled beforehand.
The shoots and leaves can also be cooked like spinach.
Sweet potatoes are generally vigorous and healthy plants, when grown in suitably warm conditions and watered regularly.
They are troubled by few pests, although when grown in a greenhouse they can be affected by red spider mites or whitefly.
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