How to Grow Sweet Potatoes
Growing Sweet Potatoes is Easy as Pie!
By Kristi Cook – Learning how to grow sweet potatoes is a rewarding task. Sweet potatoes are about as versatile of a vegetable as one can get, making this tasty root the perfect garden staple in nearly any USDA planting zone. Sweet potato pie, marshmallow-covered casseroles, and sweet potato bread are but a few of the mouthwatering dishes made possible by this humble root. And much to a gardener’s delight, learning how to grow sweet potatoes is, well, easy as pie.
Sweet Potatoes or Yams?
Sadly, the sweet potato is a victim of mistaken identity. Dating as far back as colonial times, orange-fleshed varieties have been routinely labeled as yams, yet they’re not yams at all. Sweet potatoes (Ipomoea batatas) belong to the morning glory family (Convolvulaceae), while true yams (Dioscorea L) reside in the aptly named yam family (Dioscoreaceae). In the United States, only sweet potatoes are grown commercially, with yams being relegated to specialty growers and markets. So, despite names such as “candied yams” or “fresh, local yams,” most often, these tasty treats are still the common sweet potato. No matter, though, the dishes these little roots create are simply mouthwatering, no matter what they’re called.
Start With Slips
Sweet potatoes are not grown from seed. Instead, small shoots called slips are sprouted from a sweet potato from the previous year’s harvest. Once slips reach the desired length, they are “slipped” off the root tuber and then planted in the ground. You can either purchase ready-to-plant slips from local nurseries, catalogs, or other growers, or you can sprout slips yourself from a sweet potato purchased at the supermarket. If going the grocery store route, select only organic varieties as conventionally grown sweet potatoes are often treated to prevent sprouting.
Starting your own slips is simple, though it does require a bit of planning because the process takes four to six weeks. Most sweet potatoes require 90 to 110 days to reach harvest size, so slips should be ready to plant as soon as soil temps reach 60 degrees F and all danger of frost has passed. For example, in my zone 7 garden, planting dates generally range from mid-April to the end of May, making the best times to start the slip growing process sometime between the end of February to the first week in April.
Several methods exist to sprout slips, but the two most common are the water jar and sandbox methods. The water jar method is likely the most familiar as many of us unwittingly grew slips in our elementary science classes. Simply skewer any disease-free sweet potato midway down with three or four toothpicks around the root’s circumference. Balance the potato in a water-filled jar and set it in a window or under grow lights. Make sure to change the water every few days to avoid stagnant, stinky jars, which can also affect slip growth.
Just as easy, and quite possibly my favorite way to start slips, the sandbox method offers the winter-weary gardener an opportunity to dig in the dirt. Fill a small tote, box, or flower pot with moist sand or potting soil. Nestle the sweet potato on its side in the planting medium, leaving up to half of the top exposed.
To increase heat and moisture retention, cover the top with plastic wrap to create a greenhouse effect, especially if placing in a window instead of on a propagation heating pad as the roots need consistent warmth to allow for slip production. It’s also a good idea to poke a few slits in the wrap to allow some moisture to escape slowly. This helps prevent mold issues but is not always necessary.
However, regular monitoring of the container’s moisture and heat level is necessary to ensure all is going well. You can also forgo the plastic wrap entirely by simply covering the entire root with one to two inches of sand/soil which acts as insulation and more closely mimics garden conditions. As always, keep the root and medium moist but not wet at all times.
Both methods will sprout slips within a week or so with a single potato producing up to 20 slips over three or four weeks. Once slips reach six to nine inches, cut or “slip” them off at the root. The slips are now ready to plant if garden conditions are right, or you can place the new slips in a jar of water to allow roots to develop before planting. It’s not necessary to have roots prior to planting as the slips will continue to develop once in the ground.
However, there is one drawback that I’ve found when transplanting without a decent number of roots. That is the tendency for the slips to dry out very quickly and die on that random early spring day that reaches higher than normal temps or when a drying wind is present. Because of this, I tend to opt for a longer transplant growth time and allow several inches of roots to develop prior to transplanting.
While sweet potatoes are not fussy, they do require consistently warm (60-65 degrees F) soil at planting time. Once soil temps are stable, plant slips three to four inches deep, 10 to 18 inches apart in well-drained soil (sandy loam soil is best for uniform root development) with a pH of 5.7-6.7. Learning how to check soil pH level will be helpful for not only growing sweet potatoes but for your other garden goods, too. If possible, use a simple raised bed design to provide good drainage during heavy spring rains. In dry weather, provide one inch of water weekly as needed.
Harvest and Cure
Dig roots with a spade fork before soil cools to 50 degrees F and before the first hard frost hits. Allow soil to dry on roots. Cure in a shaded, well-ventilated area between 85-90 degrees F for seven to 10 days. Then store at 55-60 degrees F in a dark location such as a closet or pantry in baskets or burlap sacks. Allow three to four weeks for the full flavor to develop before enjoying.
Easily adaptable to a variety of growing conditions, every garden has a place for a few sweet potatoes and every gardener can learn how to grow sweet potatoes. If you start your slips now, you’ll be enjoying homegrown candied yams by Thanksgiving!
Now that you know how to grow sweet potatoes, will you be adding them to your next garden? We would love to hear from you in the comments below.
Originally published in the May/June 2021 issue of Countryside & Small Stock Journal and regularly vetted for accuracy.