Culture
Sweet potato grows best in warm, dry conditions, with three months of temperatures above 20°C. Shade is needed in very hot conditions. They do not withstand frost.
Plants are commonly planted 30 to 45 cm apart in rows up to 1 metre apart. Planting may be by hand or machine (for large scale production).
The ideal soil is a well-drained sandy loam, with a pH in the range of 5.5 to 6.5. Soil must be cultivated to keep the surface loose and free of weeds. Heavy clays can result in roots that are rough and irregular in shape. Excessively light soils tend to produce long thin roots.
Cultivation after planting is minimal. Mechanical cultivation is sometimes carried out after planting, in order to control weeds, until plant growth becomes rapid. Once plants are established, they compete strongly with weeds and further cultivations cease (they would damage the crop once tubers begin forming).
Nutrient requirements:
Sweet potatoes have an average rate of nutrient uptake not heavy or light they need moderate rates of nitrogen but potassium, phosphorus, calcium and magnesium are needed in higher than normal ratios. Moderate amounts of nitrogen and higher than normal quantities of potash and phosphorus are required for growth and tuber formation.
Research has shown that a thick and more even shaped tuber is produced when fed with potash. Tubers grown without potash can be more irregularly shaped. Soils with an excessive amount of nitrogen can produce too much top growth and longer, thinner tubers.
Larger applications of both nitrogen and potash fertilisers may be needed on more freely draining sandy soils. Loams (or any soils that retain nutrients better); should be fertilised less.
If a legume cover crop has been grown and ploughed in before planting, it will have increased nitrogen soil levels; hence less nitrogen fertiliser should be applied.
Most experts recommend against using manures for sweet potato crops; though some growers use low levels of manure.
Propagation
Propagate from tubers or cuttings
Medium-sized tubers may be planted direct in a bed
Alternatively plant into a box of moist sand in a warm area. When the shoots on the sprouted tubers are 20-25 cm long, transplant them into prepared beds. Plant in rows 1 m apart, with 30-45 cm between each plant.
Another way is to strike shoots as cuttings then planted out. This may be more time consuming, but can be a way to reduce risk of disease.