How to grow sweet potatoes

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 also be available in garden centres.

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 peat-free multi-purpose compost. Slips should root quickly and easily. Alternatively, you can stand the slips in a glass of water – they will soon produce roots and can then be planted into pots. 

Place the pots of newly planted slips or plugs in a propagator or cover with a clear plastic bag, to maintain high humidity, until the plants are growing strongly. Keep them somewhere warm and bright, in consistently moist compost. Move them into slightly larger pots as they grow, watering them with tepid water.

You can take cuttings from tubers you grew the previous year, if they were stored well and are still in good condition in spring. To grow your own cuttings:

• In spring, place sweet potato tubers in moist 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 peat-free multi-purpose or cuttings compost, then place in a propagator to root (see Planting cuttings and plug plants, above)

Space sweet potato plants at least 30cm (1ft) apart, as they will produce long leafy stems

• To plant in a container – choose a pot at least 30cm (1ft) wide and fill with peat-free multi-purpose compost, then position one plant in the centre. Set it at the same depth it was previously growing, firm in gently and water well. Alternatively, plant one in a grow bag. Keep in a greenhouse or coldframe or in a very warm, sunny, sheltered spot outdoors. If possible, cover containers placed outside with a cloche or plastic-free fleece, to improve the likelihood of a decent crop.
• To plant in the ground – ideally plant them in the ground inside a greenhouse or coldframe. If planting outdoors, choose a very warm, sheltered location in full sun, with moisture-retentive, free-draining soil. Prepare the soil by forking in lots of home-made garden compost or well-rotted manure, about two bucketfuls per square metre/yard. Alternatively, if you're practicing no-dig, mulch the surface and plant directly into the mulch. If growing outside – cover the ground with cloches or plastic-free fleece to warm the soil for a few weeks before planting. Plant the young plants at least 30cm (1ft) apart, at the same depth they were previously growing, firm them in and water generously. If possible, keep sweet potatoes planted outdoors covered with cloches or plastic-free fleece – the temperature lift makes all the difference.

Sweet potatoes are thirsty plants and need regular watering in dry weather and when growing in a container. Aim to keep the soil or potting compost consistently moist. During hot weather, plants may even need watering daily. If they go short of water, the tubers won’t swell.

When growing sweet potatoes in the ground, apply a thick mulch of well-rotted manure or garden compost over the soil surface to keep weeds at bay and hold moisture in the soil. 

Sweet potatoes growing in prepared ground (with added organic matter) shouldn't need feeding, but to get a good crop from plants grown in containers, it's best to feed regularly. Apply a high potassium organic liquid fertiliser every 14 days throughout summer.

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.