There are several ways to get a sweet potato to sprout “slips”, the mini-plants that sprout from the nodes on the tuber. Many folks swear by suspending the sweet potato in glass above water; that will give you roughly two to six starter plants. But small farmers who are planting several rows of sweet potatoes have other methods—the most common among them is planting a healthy sweet potato from the previous year’s crop in soil and collecting the sprouts.
If you simply plant in a bin or bucket of potting soil, you can loosen the potato and then peel the slips off, carefully turning them sideways to keep the roots intact, and then gently separating the roots from each other. Growing slips takes about six weeks.
Some growers prefer to cut the slip off the potato without the roots, but it may take longer for the plant to get established.
Transplanting
Slips favor a warm environment, but once they are separated from the root, they should be maintained at a cooler temperature (50-60 degrees F) and moisture loss should be prevented in order to produce good yield. Slips can be planted immediately and are the healthiest if planted within six days. Larger slips, planted more deeply, may have an advantage in terms of growth above and below ground and in terms of yield.
A study from the University of Szeged Faculty of Agriculture in Hungary found that planting in ridges or hills resulted in the best yields.
Once the soil has been prepared and hilled, slips can be planted a few inches deep, leaving at least 3-4 leaves above ground. Some growers who have a lot of slips to plant make a furrow in the ridge, lay the slips in place 10-14 inches apart, and then poke the root end into the soil with a forked wooden stick. Mechanized planting tools were tried by the Kerr Center and found to be of limited benefit.
Sweet Potato Plant Care
Sweet potatoes are hardy and attract few pests, but these plants do benefit from weed suppression and even a little bit of dressing with compost around the plant once it is growing steadily.
Light, Soil, and Nutrients
Sweet potatoes need full sun and warm weather to thrive. They also require a balanced level of nitrogen, according to a study carried out at Shangdong University in China. Too little will cause the plant to form thin roots and struggle to form storage roots; too much will inhibit the activity of the adventitious root cambium, also inhibiting the formation of storage roots. Their study showed that optimal nitrogen fostered more root-forming activity and larger sweet potatoes.
Since the roots of the plant will need to spread out and swell up, the soil should be well loosened ahead of planting. Compost can help the soil structure. Sweet potatoes prefer slightly acidic soil and may be more disease prone in neutral to alkaline soils, according to the National Gardening Association.
Create ridges between 6-10 inches high and 2-3 feet across. If it’s not too big a project, a long-handled hoe will do the job, but for larger planting areas, a wheel-hoe with a hiller attachment can help. Creating loose, friable texture is especially important in clay soils.
Water
Water the plants deeply for most of the growing cycle. While drought stress will reduce the number and size of sweet potato tubers, tapering off watering at the end of the growing cycle, so that soil isn’t too heavy, will make digging them up easier
Temperature and Humidity
When planting the slips, wait until a few weeks after your last frost. They are a hot weather crop with a long growing season, and so need the soil to be at least 50 degrees F, even at night.
How to Harvest Sweet Potatoes
These are the most common sweet potato varieties to grow and cook with:
Japanese sweet potatoes have pink flesh, a light yellow inside, and a creamy consistency when baked.
Garnet sweet potatoes have red skin, deeper orange insides, and a dense, smooth texture when cooked.
Jewel sweet potatoes have light, pink-orange skin and bold orange inside, featuring that slightly carrot-like, traditional “holiday yams” flavor.
Hannah sweet potatoes have pale, pink-tan skin and cream-colored insides. This variety is drier and flakier than others but has a honey-sweet taste.
Purple sweet potatoes, such as the Okinawan, are purple all the way through, dense, dry, sweet, and considered a super food.
After harvesting, sweet potatoes have to “cure” for seven to 10 days at 80-90 degrees F and with adequate humidity. Uncured sweet potatoes are likely to dry out and not store well.