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.
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.
- Botanical Name: Ipomoea batatas
- Common Name: Sweet potato, Yam (used incorrectly)
- Plant Type: Many varieties are perennial, but they are grown as an annual vegetable
- Mature Size: Vines can easily spread 20 feet and the tubers average about 4 to 6 inches.
- Sun Exposure: Full sun to partial shade
- Soil Type: Slightly acidic soil
- Soil pH: 5 to 6.5
- Bloom Time: 3 to 4 months from when planted
- Flower Color: White, pale to deep lavender
- Hardiness Zones: 8 to 11
- Native Areas: Tropical Americas
How to Grow Sweet Potato Plants
Sweet potatoes 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. Plant sweet potato slips as soon as the ground has warmed and all danger of frost has passed. 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.
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.
Plant in a soil high in organic matter and then leave them alone. To give them a head start, sweet potatoes are often planted in raised rows, about 8 inches 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.
Once established, sweet potatoes will tolerate growing in dry soil. It's best to keep it evenly moist with an inch of water once a week. Don't water your sweet potatoes during the final 3 to 4 weeks prior to harvest in order to keep the mature tubers from splitting.
Temperature and Humidity
Sweet potatoes should not be planted outdoors until the temperature of the soil has warmed to 60 degrees Fahrenheit. They need soil growing temperatures between 60 to 85 degrees Fahrenheit and an air growing temperature of 65 to 95 degrees Fahrenheit.
Feeding sweet potatoes tend to produce just foliage. You can add compost to the beds before planting the sweet potatoes.
Varieties of Sweet Potatoes
- Beauregard: This produces a potato with pale reddish skin and dark orange flesh; it's a popular commercial variety that takes 100 days until maturity.
- Bush Porto Rico: Yields a potato with copper skin and orange flesh. The compact vines with big yields are good for smaller gardens. Takes 110 days until maturity.
- Centennial: This has good disease resistance and relatively quick maturing; takes 90 to 100 days until maturity.
- Georgia Jet: A type with reddish skin and orange flesh. This is a good choice for a shorter season; takes 90 days until maturity.
- Patriot: This is known for copper skin and orange Flesh. Great pest resistance makes it a good choice for organic gardens; takes 100 days until maturity.
- Ruddy: This type has better pest resistance (insects, diseases, and nematodes) than Beauregard; takes 100 days until maturity.
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.
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
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.