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 warm-weather perennial 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 potato and yam 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 four 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|
|Plant Type||Herbaceous perennial, but usually grown as an annual vegetable|
|Mature Size||Vines spread to 20 feet; tubers average 4 to 6 inches|
|Sun Exposure||Full sun to part shade|
|Soil Type||Medium-moisure, well-drained soil|
|Soil pH||5 to 6.5 (slightly acidic)|
|Bloom Time||3 to 4 months from when planted|
|Flower Color||White, pale to deep lavender|
|Hardiness Zones||8 to 11 (USDA)|
|Native Areas||Tropical Americas|
How to Grow Sweet Potatoes
Sweet potatoes growing for consumption are usually planted from purchased slips—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.
Sweet potatoes will generally thrive in any average well-drained soil in a sunny location. These plants are tropical in origin, so wait until the soil has warmed up fully before planting. If your soil is too dense or rocky, consider planting sweet potatoes in raised beds filled with a sandy but rich potting soil. 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.
Keep the plants moist, especially during dry spells. Three to four months after planting, the tubers should be ready to harvest for eating.
Be sure to plant your sweet potatoes in full sun to part shade. They generally prefer full sun but appreciate some afternoon shade in hot, dry regions.
Sweet potatoes prefer soil that is well-drained but high in organic matter. Sandier soil is preferable to dense, clay soil.
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 three to four 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.
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 popular commercial variety produces a potato with pale reddish skin and dark orange flesh that takes 100 days until it reaches maturity.
- 'Bush Porto Rico': The compact vines yields a potato with copper skin and orange flesh after 110 days. This variety has big yields, so are good for smaller gardens.
- 'Centennial': This type has good disease resistance and is relatively quick to mature, averaging about 90 days to reach maturity.
- 'Georgia Jet': Known for its reddish skin and orange flesh, the Georgia Jet is a good choice for a shorter season because it only takes 90 days to reach maturity.
- 'Patriot': This potato is known for its copper skin and orange flesh. The Patriot's great pest resistance makes it a popular choice for organic gardens.
Propagating Sweet Potatoes
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.
The tubers are ready to harvest in about four 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 when growing sweet potatoes 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.