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 this warm-weather perennial vining plant. Edible sweet potatoes are closely related to morning glories (Ipomoea tricolor) and are the same species as the sweet potato vining plants commonly grown as ornamentals. The edible and ornamental types are different cultivars of Ipomoea batatas
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 are slow-growing and are always planted in spring because they 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-moisture, well-drained soil|
|Soil pH||Acidic (5 to 6.5)|
|Bloom Time||3 to 4 months after planting|
|Flower Color||White, pale to deep lavender|
|Hardiness Zones||8 to 11 (USDA)|
|Native Areas||North America, South America|
How to Plant Sweet Potatoes
Sweet potatoes grown for consumption are usually planted from purchased slips—small rooted pieces of a tuber—or from tubers that you root at home. 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 slips from a reputable seed supplier. Plant slips 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.
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.
Sweet Potato Care
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 1 inch of water given once a week. Don't water your sweet potatoes during the final three to four weeks prior to harvest to prevent 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.
Sweet potatoes are not heavy feeders, but it's important to give them balanced nutrition, typically with proper soil preparation. Overfeeding tends to promote growth of foliage rather than tubers. The best approach is to add compost to the beds before planting the sweet potatoes. Alternatively, you can apply an organic liquid fertilizer to the soil prior to planting.
Sweet Potato Varieties
- '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': This compact vine yields a potato with copper skin and orange flesh after 110 days. This variety has big yields, so it's a good choice for smaller gardens.
- 'Centennial': This cultivar offers good disease-resistance and is relatively quick to mature, averaging about 90 days to maturity.
- 'Georgia Jet': Another fast-maturing variety, 'Georgia Jet' is prized for its reddish skin and orange flesh; it matures in about 90 days.
- 'Patriot': Outstanding pest-resistance makes this variety a popular choice for organic gardens. The potatoes have copper skin and orange flesh.
Sweet potato tubers are ready to harvest in about three to four months, depending on the cultivar. 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 up 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.
If your winters are longer than a couple of months, you can save tubers over the winter and plant them the following spring. Dig up the tubers before the first frost in fall. Store them over the winter in peat, vermiculite, or other dry material, and keep them in a cool, dry place without light (such as a basement or root cellar). In spring, the tubers will start to sprout. Divide them into pieces, making sure that each piece has at least one eye. Plant them in the garden after the threat of frost has passed and the soil temperature is at least 60 degrees Fahrenheit.
If you live in an area with short winters, you can begin new slips from vine cuttings. Snip off about 6 inches from the tips of the vines, before the first frost. Place the cuttings in water; once they develop roots, plant them in soil in pots and keep them in a sunny location until it’s time to plant them outdoors.
You can also create slips from a full-grown sweet potato. Cut it in half lengthwise and place each half on a bed of damp potting soil. Cover the pieces with a few inches of soil and keep it 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).
Common Pests and Diseases
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 sweet potato slips. Rotating their location in the garden from year to year also helps. Mice can also be a problem, so be on the lookout.