They have trailing stems that can reach up to 3 m if left un-pruned. Cultivars vary considerably in leaf shape and tuber size, shape and color. Most cultivars are short-day plants. Tubers are eaten cooked and the leaves may be used in the same way as spinach.
For best results grow them in highly fertile, well-drained, sandy loams with a pH of 5.5-6.5 and medium to high nitrogen levels. Water and weed regularly, mulch to conserve moisture. Train shoots to spread around the plant. Apply a general-purpose fertilizer at two to three weeks intervals until the tubers have formed. Protect the plants from winds.
In tropical and subtropical areas plant sweet potatoes at the start of the rainy season. In warm and temperate areas plant them in spring. Make raised ridge about 75 cm apart and plant tubers 5-7 cm deep in the ridge spacing them 25-30 cm apart. Also you can take 20-25 cm long stem cuttings from mature plants and insert them to half their length just below the apex of the ridge.
You can also sow seeds. Cultivars raised from seeds will provide reasonable crops. Sow indoors in trays or 21-25 cm pots at a temperature of at least 24 Celsius degrees (75 F). When seedlings are about 10-15 cm high harden them off and transplant outside. If you cannot grow them outside transplant the seedlings to growing bags or prepared beds under cover.
Also under cover you can grow sweet potatoes from cuttings. Insert 3 or 4 into 15 cm pots. Maintain a minimum temperature of 25 Celsius degrees (77 F) and a humidity of over 70 per cent by damping down regularly. When roots develop transfer the plants to greenhouse beds or growing bags. Water regularly and remove the growing points of shoots longer than 60 cm to encourage the growing of lateral shoots. Keep the temperature below 28 Celsius degrees (82 F) and the growing area well ventilated.
Harvest 12-16 weeks after planting when the stems and leaves turn yellow. Crops from seeds are ready three or four weeks later. Lift the tubers with a fork without damaging them. Before storing them they need to be cured 4-7 days at 28-30 Celsius degrees (82-86 F) and a humidity of 85-90 per cent. They may be stored in shallow trays at 10-15 Celsius degrees (50-59 F) for several months.