Sweet potatoes (Ipomoea batatas), members of the morning glory family, are grown from sprouts called slips. Be sure to order slips from a source that offers certified disease-free stock, because slips have been known to carry harmful diseases, including black rot. (We’ve listed reliable sources further down the page.) Planting and growing sweet potatoes is straightforward, but we’ve gathered these tips to make sure you get a sweet harvest next year:
Choose the right variety of sweet potato
Heirloom varieties taste better than more recent introductions, says Glenn Drowns, who grows 86 sweet potato varieties at the Sandhill Preservation Center in Calamus, Iowa. Drowns’ favorites are ‘Betty’s’, ‘Frazier White’, and ‘Ivis White Cream’. But those may not be the best choices for your garden. If you live in a cool-season climate, select a short-season variety (see “Cool-Season Tricks” below for specifics). In the South, plant a mixture of short- and long-season varieties and you can harvest sweet potatoes for several months. If you or other gardeners in your area have had problems with diseases affecting sweet potatoes, you can solve that the organic way by choosing resistant varieties. Root-knot nematodes and fusarium wilt, for instance, are prevalent in many areas of the South. ‘Excel’ (with orange flesh), ‘Jewel’ (deep orange), ‘White Regal’, and ‘Topaz’ resist these plagues. If you have very limited space, try a bush variety, such as ‘Porto Rico’ (light red) or ‘Vardaman’ (red orange).
Rotate the crop
“The most important thing gardeners should do is rotate,” states Danielle Treadwell, Ph.D., an organic and sustainable farming specialist at the University of Florida. Plant sweet potatoes in a different location every year to discourage wireworms, which will bore into the tubers and blemish them cosmetically (though they are still edible), and diseases such as black rot and scurf, which cause postharvest rotting. Don’t use the same space for sweet potatoes more than once every four years. If you have a small garden, consider growing them in containers and changing the soil each year.
Feed your soil
Grow cover crops—“green manure” plants that add organic matter and nutrients to your soil—to feed your sweet potatoes gently and steadily without additional fertilizers. The tuberous roots need no more nitrogen than is supplied by legume cover crops, such as field peas, says Treadwell. Mix seeds of a winter annual legume (field peas) with a cereal grain such as oats or rye. A 1-to-3 ratio of peas to grain will deliver enough, but not too much, nitrogen. Plant in fall, and when the legume blooms, mow down the cover crop and turn it 8 inches into the soil. This combination slowly releases nutrients into the soil, Treadwell says. Get a soil test to determine if you need to add other essential nutrients, such as phosphorus and potassium, or adjust your soil pH. “Sweet potatoes thrive where the pH is 5.6 to 6.5,” says Rosie Lerner, a consumer horticulture specialist at Purdue University.
If you’re not ready or able to grow cover crops in your garden, spread a 2-to-3-inch layer of finished compost on the bed where you want to plant sweet potatoes. Gently scratch the compost into the top 6 inches of soil before planting. The compost will nourish your sweet potatoes, balance the soil pH, discourage diseases, and help with moisture management. (How’s that for multitasking?)
Sweet potatoes grow best in warm soil and hot weather, Drowns says. Mound the soil in your bed into ridges. This helps heat up the soil in spring and also allows rainwater to drain away, protecting the tubers from rotting. Mound ridges two weeks before planting—18 inches wide and 10 inches high on light soils, 12 inches wide and 15 inches high on heavier soils. Allow 3 feet between rows.
Leave space between. Plant slips on the top of mounds, burying them up to their first set of leaves. Space plants 12 to 18 inches apart. Keep slips consistently moist for a week after planting.