Ipomoea batatas

Convolvulaceae

Sweet Potato

A vigorous perennial vine native to tropical America with large, edible tubers.

Uses

Cook -baked, fried or boiled.

Suitable for chips, hash browns, mash.

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). 

‚ÄčThe 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.

 

Cultivars

Sweet potato varieties may be classified in various ways:

  • Food types – varieties grown primarily for humans to eat. These are often divided into soft or dry fleshed varieties.
  • Feed types – grown for livestock

Dry or firm Fleshed types have a firmer flesh after cooking.
Soft or Moist Fleshed varieties have a softer flesh after cooking. These are of greater commercial importance in many countries, including the USA. The soft fleshed cultivars are sold as “Yams” in the USA, however, these are not yams.

 

Plant Health

Several insect problems including Moth grubs, beetles and weevils may be a problem.  Fungal diseases that cause rots, leaf spots, rust and fusarium wilt can occur. 

Black Rot causes dark depressions in the sweet potatoes, and black cankers on underground stems. Crop rotation and use of disease free seed greatly reduces any issue.
Internal cork can develop if stored at a high temperature. This involves tuber flesh becoming dry and corky in appearance. Some cultivars are less susceptible.

Pox causes soil rot depressions on tubers, thin yellowing leaves and overall stunting of the plant growth. The problem is reduced by improved hygiene, crop rotation and lowering soil pH (adjust pH carefully to 5.2 with sulphur).

Stem rot may start as yellowing between veins on the leaf, followed by wilting of vines and deterioration of stems. Hygiene and crop rotation are important to avoid this.

 

More info

Harvest when the plant is completely yellow and the tubers have a firm skin – normally 3 to 6 months after planting. Store the tubers at 10-12°C in a dark, well-ventilated position, but not in the fridge.

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