How to Grow and Care for Sweet Potatoes
Introduction
Sweet potatoes (Ipomoea batatas) are a long-season, tropical vegetable, so it's no surprise that they're grown mostly in southern states. However, it's also possible for northern gardeners to grow these tasty, highly nutritious vegetables. Most sweet potato varieties require at least 4 frost-free months to grow big potatoes. Plants yield best if night temperatures average 72 degrees F.
However, sweet potatoes are not just for the dinner table! There are also ornamental varieties. These ornamental varieties do produce tubers, but these tubers do not taste good and are mostly starch. Instead, use these ornamental varieties as groundcovers or container plants.
Sweet potatoes belong to the morning glory family (and are not closely related to true potatoes), and if you see their flowers, you can definitely see the resemblance. All sweet potatoes, whether ornamental or edible, are tender plants that thrive in hot weather, can't take frost, and refuse to grow in cool soil. Thus, they should be planted as early as possible to get the most out of them.
Propagation
Since sweet potatoes rarely set seed, they are instead grown vegetatively. The ornamental varieties are usually grown from cuttings, and the edible varieties from "slips," or sprouts, which are available at nurseries in southern states or by mail. If you are growing your own slips or cuttings, begin sprouting them about 8 weeks before planting.
To start slips, suspend a sweet potato in water with toothpicks. The sweet potato will begin to grow roots and shoots. Change the water regularly to avoid the risk of the sweet potato rotting. Plant when the weather has warmed up and the slip is a few weeks old.
For cuttings, take a stem from a parent plant. Leave only a few leaves at the top, and set the cutting in water, changing the water regularly. It will grow roots and leaves. When the weather has warmed up and the cutting is a few weeks old, plant the cutting in the soil.
Choosing a site to grow sweet potatoes
For both the ornamental and edible varieties, select a site with full sun and well-drained soil. Prepare the garden bed by using a garden fork or tiller to loosen the soil to a depth of 12 to 15 inches, then mix in a 2- to 4-inch layer of compost.
Planting Instructions
For edible varieties, unless the soil is very sandy, raise the planting bed 6 to 8 inches to make a ridge 1 foot or so wide. After danger of frost is past and the weather is warm (nights above 55 degrees F), set slips 12 to 18 inches apart along ridges or in rows that are 36 to 48 inches apart. Set the slips in the soil to the depth of the first leaves with several nodes (joints) underground. Firm the soil and make a shallow depression around the plant. Water beds generously for a few days.
For ornamental varieties, make a hole that can accomodate the root ball. In order to let the plant adjust to its new environment and recover from transplant shock, water it thoroughly and don't let it dry out. The leaves may appear droopy for the first few days after planting, but it will eventually recover.
Ongoing Care
For edible varieties, control weeds by hoeing or mulch the area 4 to 5 weeks after planting. Provide deep watering in hot dry periods to increase yields. If planning to store part of the crop, don't give the plants any extra water late in the season. Contact your local County Extension office for controls of common sweet potato pests such as flea beetles. If you live in a cool climate, protect sweet potato vines from late-season frost. If vines suffer frost damage, they can transfer rot to the roots below ground.
For ornamental types, fertilize monthly to encourage growth. Keep the soil moist and trim back if needed. Sweet potatoes are very tenacious plants but are also easily manageable. Use them to spruce up neglected areas of the garden. These plants grow quickly and often outcompete weeds without any additional help.
How to harvest sweet potatoes
Sweet potato plants will keep growing as long as the weather stays warm. The vines don't die and signal harvest time the way white potato plants do. If you garden in a hot climate that has a long growing season, you just have to keep checking the hills and harvest the roots at the best cooking stage.
It's best to dig sweet potatoes on a dry, overcast day, or at least shade the unearthed roots from direct sun.
Let the potatoes dry on the ground for a couple of hours. Don't wash the potatoes after the harvest, either. Sort any badly cut or bruised potatoes to eat first.
Sweet potato flowering and seeds
Sweet potatoes mostly focus on vegetative growth and do not flower often. Some varieties do flower more than normal (for example, the ornamental varieties 'Sidekick Black Heart' and 'Blackie'), but in general, sweet potatoes cannot be forced to flower and will only flower if they feel like it.
Sweet potato seeds are even rarer and are mostly ever only used in breeding programs. If sweet potatoes are grown from seed, they will not come true to their parent. Sweet potatoes will not set seed unless the plant is cross-pollinated.
Sweet potato seeds are the only inedible part of the plant. They are highly toxic and contain LSA (a compound similar to LSD). All other parts of the plant are edible, including the stem, tubers, and leaves.
