Sweet Potato
Vegetable Farming in South Africa

© Louise Brodie

Sweet potato (lpomoea batatas) is not related to the common potato. Sweet potato belongs to the morning glory family and produces edible storage roots. The crop plays an important role in food systems of Southern Africa countries, including South Africa. Sweet potato is an important food and poverty relief crop that can be used to combat widespread Vitamin A deficiency which compromises the immune system and eye health.

Different sweet potato cultivars can be divided into two main types:

Those with a dry flesh when cooked

Those with a moist (soft) flesh when cooked

The storage roots can be found in different colours. The skin can for example be white, yellow, pink, orange, purple or reddish brown. The flesh colour varies from white and yellow to light orange or dark orange. Orange-fleshed cultivars are rich in beta-carotene and thus used in food-based programs to address vitamin A deficiency. Sweet potatoes are rich sources of energy but also contributes vitamin C and minerals such as magnesium, copper, iron and zinc to the human diet. The leaves provide additional proteins, vitamins and minerals.

Soil

Sweet potatoes grow well in sandy-loam, loam or clayey-loam soil. The crop needs good drainage and is sensitive to waterlogging, salinity and alkalinity. Optimum pH (H20) is 5.6 - 6.5.  Stony or clay soil is not good, as it does not allow the formation (development) of good storage roots.

Climate

Sweet potato is a warm season crop, which means that warm days and nights are essential for optimum growth and development. Sweet potatoes are sensitive to low temperatures, especially frost. Sweet potato can be grown in all South African provinces if supplementary irrigation is provided. The plant is somewhat drought tolerant once the storage roots have formed.

Cultivars

Orange-fleshed: lmpilo and W-119 (dry); Beauregard (moist) Purple skin (fresh market): Blesbok, Bosbok (moist) Cream skin:  Ndou, Monate (dry)

Propagation

Propagation is by stem cuttings. Pieces of stem of 20-30 cm long should be taken for cuttings. The leaves may be removed from stem cuttings before planting, but it is not necessary. Top cuttings are more vigorous than cuttings from the other parts of the vine. Sometimes cuttings are prepared from storage roots: Plant the storage roots just covered with soil. When sprouts are 25-30 cm long, break them off and use for planting.

Cut 20-30 cm healthy, insect and disease free cuttings with a clean pruning shear or sharp knife.   Plant them in your prepared bed by covering half of its length in wet soil. Press surrounding soil firmly so that the soil should come in good contact with the stem, thus promoting quick root development. Water the plants immediately after planting. Always cut shoots from a healthy plant. Do not use vines from volunteer sweet potatoes because these might transport pests and diseases.

Soil Preparation

Loosen the soil thoroughly by either ploughing or using a fork, hand hoe or spade. Loosen the soil to a depth of 250-300 mm for good root aeration, root penetration and drainage. Remove stones and break hard layers to ensure good root penetration. All clods should be smashed by using a rake or hand tined cultivator until a deep fine bed is obtained.
Cover crops (green  manure) can be planted and worked into the soil 3-4 months before establishing the crop.

By Louise Brodie