You can either plant rooted shoots or vine cuttings. But make sure the material is disease-free, because the sweet potato plant is very vulnerable to viral diseases, where an organism (virus) gets into a plant’s cell and basically destroys the plant from within.
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This involves using a few well-shaped roots from your previous crop or those bought from a registered nursery. Buying from a nursery can be expensive, but the material is guaranteed to be disease-free.
- Plant close together in a seedbed in July to August.
- Cover with a 5cm layer of soil.
- When the shoots appear, increase watering.
- The shoots are ready for planting when they are 20cm to 30cm long (in five to eight weeks). Simply pull them off for planting.
- Plant them 30cm apart on ridges 90cm apart.
- Cut runners or vines into 30cm to 40cm lengths.
- Plant the cuttings up to half their length 30cm apart in ridged rows 90cm apart.
- Press down the soil firmly to ensure good growth.
- Increase watering when the shoots appear.
- With both rooted shoots and vine cuttings, you can plant the crop successfully on level soil, but you get a better yield with flattened ridges.
- On sandy soils, the ridges should be 30cm high, and 40cm high on heavier soils.
- Pay special attention to the space between shoots or cuttings when planting – the closer the spacing, the smaller the sweet potato tubers will be.
- Water the plants immediately after planting – it’s important to keep the soil moist until the plants are well-established.
- Stop watering two to three weeks before lifting, otherwise the sweet potatoes may rot.
- Weed regularly, especially while the plants are still young.
- As the plants grow, draw up soil to the main stem to ensure a good yield and to prevent the sweet potato weevil from reaching the roots through cracks in the soil.
- Leaf mottle is caused by a virus, and leaves will have lighter and darker lesions. Remove and destroy plants infected with it.
The crop can be harvested when the roots are big enough, usually three to five months after planting, depending on the cultivar. If the vines are still green, cut them off, but not earlier than two to three weeks before harvesting. This makes it easier to lift the tubers.
The vines can be used to make new cuttings or as stock feed, because they’re very nutritious.
Use a garden fork to lift the tubers. “Be very careful not to damage them, because damaged tubers may rot when they’re stored or marketed,” says the agriculture department.
Sweet potatoes do not store very well unless well cured. If you have a large enough crop to sell, cure the tubers by placing them in small heaps on the land for about seven days to dry off. Cover them lightly with vines to prevent sun damage.
If you have a small crop, lift only as many as you need each time.
Source: The agriculture department’s Directorate: Agricultural Information Services.