Versatile and becoming increasingly popular, sweet potatoes are well worth trying outdoors in milder areas – or in a glasshouse or polytunnel elsewhere. Even in mild regions, indoor growing will produce more reliable crops.

Sowing

Sweet potatoes are best grown from cuttings or slips ordered from a mail order supplier.
You can try growing them from shop-bought tubers. Many shop-bought tubers are also treated with an anti-sprouting agent, so give them a good scrub to clean them first. Then place them in moist sand in a hot propagator or even in the airing cupboard. Once the sprouts/shoots are 5-7.5cm (2-3in) long, they can be removed as cuttings.

Growing

Plants ordered as cuttings or slips are delivered from late April onwards. Pot them immediately upon receipt into small individual pots with multipurpose compost. If the slips are not rooted, simply cover the pots with a clear plastic bag or place in an unheated propagator until roots appear.
Grow the plants on in a well- lit, frost-free, spot until early June. In mild regions, sweet potatoes can be planted outdoors after a period of hardening off. They require a highly fertile but light, preferably sandy, soil. If your soil is not naturally sandy or free-draining, plant into ridges 15-30cm (6-12in) high, spacing plants 30cm (12in) apart, with 75cm (2.5ft) between rows.
Sweet potatoes crop best at temperatures between 21-26°C (70-80°F). Keep well watered, feeding every other week with a high-potassium liquid feed.

Harvesting

Tubers take from four to five months to mature. They can be lifted from the end of August, but it is better to leave them until the leaves begin to yellow and die back.