Growing sweet potatoes

Sweet potatoes originate from South America. Their heat tolerance makes them a useful summer crop for areas that are too warm for most vegetables.

Growing sweet potatoes
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It’s a pity their popularity has waned over the past couple of decades in South Africa.

We used to see vendors with bags of sweet potatoes at intersections throughout the Lowveld – but no more. Perhaps the new and improved ARC varieties will see the vegetable brought back into favour – and flavour!

Growing sweet potatoes

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Sweet potatoes are planted into ridges spaced 1m apart. Fertiliser and/or manure can be incorporated or directly ridged where possible. Harvest or buy runners about 30cm long. If too long, they can be broken up into the required lengths.

Tip runners are slightly higher-yielding, but only by about 3%, so most growers use runners and tip runners, unless they have surplus planting material. Because freshly harvested runners are brittle and can break easily, it’s safer to allow them to wilt slightly before planting.

This can be done on the land when planting commences. Plant only when the runners are flaccid enough to be pushed into the soil without snapping.

The procedure is as follows. Place the runners transversely across the ridge 30cm to 40cm apart. A stick with a notch at the end is used to secure the runner, which is then pushed into the soil from the top of the ridge until the two ends protrude above the soil.

You can also push in the runner from the broken stem end, leaving more of the runner above ground.
However, this means more of the runner will dry out before rooting and there’s a smaller area to develop roots. To prevent this keep the surface of the soil moist by frequent, light irrigations.

Many weedkillers will work on a pre-emergence basis. Regardless of whether or not a pre-emergence weedkiller is used, any germinating weeds can be taken out at the two-leaf stage by using Paraquat at 0,5â„“/ha without a wetter or sticker. Irrigate as soon as planting is complete.

This crop is resistant to most weedkillers. Sweet potatoes are the same family as morning glory which is notoriously difficult to control with most herbicides.

Do a light re-ridging just before damage will be done to the new growth. Very often this and the Paraquat will be sufficient to keep weeds at bay. As soon as the newly planted runners start sending out new shoots, apply a LAN top dressing to get them off to a good start and encourage rapid coverage of the soil surface.

This will smother weeds and enable plants to make maximum use of sunlight as soon as possible for a good yield and uniformity. An uneven stand becomes a problem with marketing as there’s variation in maturity and size.

After the runners have covered the whole area, be sure to monitor the nitrogen levels – leaf-colour must be green, but not overly lush.

It’s also important to lift when the sweet potatoes are the right size for your market. Sweet potatoes are a hardy crop and more forgiving of malpractice than other vegetable crops. Stick to the basics, and you’ll find sweet potatoes easy and economical to grow.

For more information on new varieties and planting material, contact the Agriculture Research Council on 012 841 9611.