Sweet potatoes may be associated with the southern U.S., but they will grow in just about any garden. The part we eat is the tuberous root of a vining plant that is closely related to morning glories (Ipomoea tricolor) and you’ll easily see the similarity in leaves to the sweet potato vines we now grow as ornamentals.
What Are Sweet Potatoes
Although the terms sweet potatoes and yams (Dioscorea sp.) are used interchangeably in the U.S., they are two entirely different vegetables. They are also unrelated to regular potatoes. The orange-fleshed sweet potatoes are the most familiar, but sweet potatoes can be white, yellow, and even purple.
Sweet potatoes require 4 months of warm temperatures to develop full-size tubers, but they are surprisingly easy to grow. Since the vines root wherever they touch the ground, a few plants can produce a generous harvest. There are also bush varieties, for smaller gardens.
Growing Sweet Potatoes
Sweet potatoes like a slightly acid soil, preferring a soil pH between 5.0 and 6.5. They are usually grown from slips, which are small rooted pieces of a tuber.
You can create your own slips by slicing a sweet potato in half lengthwise and placing it on a bed of damp potting soil. Cover the pieces with a few inches of soil and keep moist and warm. Small roots should develop within a few days, followed by leaves.
They are ready to be lifted and planted once they’re between 4 and 8 inches tall (about six weeks). You can try growing sweet potatoes from the grocery store, but the only way to be certain you have certified disease-free roots is to buy them from a reputable seed supplier.
If you have a short winter, you can begin new slips from vine cuttings. Snip off about 6 inches from the tips of the vines, before frost. Place these cuttings in water. Once they develop roots, plant in soil and keep them in a sunny location until it’s time to plant them outdoors.
When to Plant Sweet Potatoes
Plant sweet potato slips as soon as the ground has warmed and all danger of frost has passed. To give them a head start, sweet potatoes are often planted in raised rows, about 8" high. This helps the soil warm faster and keeps them well drained. If you are gardening in a cooler climate, spreading black plastic on the soil will also help it warm faster.
Space plants about 12 to 18 inches apart with 3 to 4 feet between rows. The vines will spread and fill in, so give them plenty of room.
Feeding sweet potatoes tends to produce just foliage. Plant in a soil high in organic matter and then leave them alone. Don't water your sweet potatoes during the final 3 to 4 weeks prior to harvest, to keep the mature tubers from splitting.
Sweet Potatoes' Hardiness Zones
Although many varieties of sweet potatoes are perennial in USDA hardiness zones 8-11, since we dig the whole plant at the end of the season to get the tubers, sweet potatoes are grown as an annual vegetable. Their size will depend on the variety of sweet potato; vines can easily spread 20 feet and the tubers average about 4 to 6 inches.
Be sure to plant your sweet potatoes in full sun to partial shade. They generally prefer full sun but appreciate some afternoon shade in hot, dry regions.
The tubers are ready to harvest in about 4 months. If you like to eat the leaves as greens, you can do so in moderation throughout the season. Be sure to leave enough to keep the plant growing.
- Beauregard - Pale reddish skin with dark orange flesh. Popular commercial variety. (100 days)
- Bush Porto Rico - Cooper skin with orange flesh. Compact vines with big yields. Good for smaller gardens, (110 days)
- Centennial - Good disease resistance and relatively quick maturing. (90-100 days)
- Georgia Jet - Reddish skin with orange flesh. Good choice for a shorter season. (90 days)
- Patriot - Copper skin/Orange Flesh. Great pest resistance. Good choice for organic gardens. (100 days)
- Ruddy - Better pest resistance (insects, diseases, and nematodes) than Beauregard. See photo. (100 days)
Harvesting Sweet Potatoes
You can dig your tubers once the foliage starts to yellow. If the foliage is hit by a frost, the tubers are probably still fine. Just don’t let them sit in the ground too long after the tops die back or they could start to rot.
Be gentle when digging. Sweet potato tubers grow close to the surface. Their skins are tender and can be damaged and bruised easily
Sweet potatoes can tolerate periods of drought, but regular watering is the best way to prevent splitting.
Pests and Problems for Sweet Potatoes
Wireworms and root-knot nematodes are the biggest problems in home gardens. Damage is lessened if you rotate your crop each year.
Many diseases can be avoided by choosing disease-resistant varieties and using certified disease-free seed sweet potatoes. Rotating their location in the garden, from year to year, also helps.
Mice can also be a problem, so be on the lookout.