Sweet potatoes are tropical plants that grow best when it’s hot. The plants are sensitive to shade which leads to low yield. However, for maximum root filling to occur, the temperature should be between 25-32°C. Higher temperatures slow photosynthesis leading to vegetative growth (lots of kalembula) and not for tuber filling.
Preparing to plant
Sweet potatoes typically grow from slips, which are shoots that are grown from a mature sweet potato. You can buy slips or grow your own. To grow your own slips, be sure to find out if you’re getting a bush type or a vining type sweet potato.
To grow your slips, start with several healthy, clean sweet potatoes. Each potato can produce up to 50 slip sprouts. You can cut the sweet potato into large sections or use whole. Place each section in water with half of the potato below the water and half above. Because the slips need warmth, place them on a window ledge or on top of a radiator. In a few weeks your potatoes will be covered with leafy sprouts on top and roots on the bottom.
You then have to separate them into plantable slips. To do this, carefully twist it off each sprout from the sweet potato. Take each sprout and put it with the bottom half of the stem submerged in water and the leaves hanging out over the rim of the bowl. Within a few days roots will emerge from the bottom of each new plant. Once that happens, you are ready to plant. Remember to keep the water fresh and discard any slip that isn’t producing roots or looks like it’s wilting. You can also get slips by planting halfway in soil for a couple of weeks.
Soil and planting
Growing sweet potatoes works best in loamy, well-drained preferably sandy soil to form large tubers. You don’t want the roots to face resistance when they try to expand in the soil. Ideally the pH has to be between 5.8 and 6.2, although they will tolerate a more acid pH to 5.0. Before planting, mix in a 2.5 cm layer of compost and thoroughly dampen the bed. If your soil is heavy clay, raise the beds amended with compost and sand. However, potatoes in clay are sometimes thinner and oddly shaped. Good root development depends on there being plenty of air space in the soil (good aeration). Shade plants if they wilt too much after planting them in the heat.
Plant sweet potatoes about 30 to 45 cm apart, and allow 100 cm between rows so the vines will have plenty of room to run. If you plant your sweet potatoes when it’s very hot and sunny, cover the plants to shield them from baking sun.
Once all of the slips are in place water them. You’ll need to give them a thorough soaking until all of the surrounding dirt is wet everyday for the first week and every other day the second week. Each week the watering will get a little farther apart until you’re watering once a week.
Thoroughly weed your sweet potatoes 2 weeks after planting by pulling them gently; if possible avoid deep digging with a hoe or other tool that disturbs the feeder roots that quickly spread throughout the bed.
Historically, sweet potatoes have been a poor soil crop that produces a decent harvest in imperfect soil, but will do much better with a little fertilizer. About 2 weeks after planting, feed plants with a fertilizer that contains potassium (the third number on the fertilizer label), such as 5-10-10. Use about 2 cups 5-10-10 per 900 square cm. Gently scratch the fertilizer into the soil surface. Then mulch over the soil with an inch of grass clippings or another biodegradable mulch. Continue weeding and adding more mulch for another month. After that, sweet potatoes can can withstand drought but they’ll produce less, though they do benefit from weekly deep watering during serious droughts.
Sweet potatoes are usually ready to harvest just as the ends of the vines begin to turn yellow. Most sweet potato varieties mature between 14 to 18 weeks after planting. Lift tubers after removing vines using hand forks, separate and sort tubers according to market requirements and pack in crates.