Growing Sweet Potatoes

The sweet potato is a warm weather vegetable and a native to Central and South America. The orange fleshed varieties are most commonly available in our area however some cultivars are white and red and are rich in vitamin A. Although they look a lot alike, the sweet potato is not related to the yam. The yam is an entirely different specie.  The sweet potato is actually related to the morning glory, can be grown in bush or vine variety and likes a long growing season.

Sweet potatoes are started from plants called “slips”. You can grow your own plants by placing several sweet potato roots several inches apart in a hotbed and then cover them with about two inches of sand or light soil. Add another inch of sand or soil when the shoots begin to appear.  The soil will need to be kept moist but do not allow it to get water logged. The soil temperature should be kept at 75 to 80 degrees and in about 6 weeks you will have plants that are ready to pull. The sprouts (slips) are then planted directly into the garden as soon as the soil warms up after the last frost. To prevent diseases, plant varieties with multiple resistance, use “certified “plants and rotate their location, not growing them in the same place for three to four years..  

Sweet potato roots prefer fertile, well drained, sandy soil which is moderately to slightly acidic with a pH of 5.6 to 6.5. Set the plants 12 to 18 inches apart in a wide (18”), raised ridge about 8 to 10 inches high. A raised ridge will dry better during the spring and it will warm up faster than an unraised area. To speed up early season growth, spread black plastic mulch over the planting area. The black plastic will capture and store more of the sun’s heat in the soil. Allow 3 to 4 feet between rows as the vining varieties need a lot of space.

Sweet potato plants are sensitive to cool soil so transplant them to the garden three to four weeks after the last frost. It is best to purchase or harvest plants the same day you plan to set them in the garden. If the weather is hot and sunny, set the plants in the garden in the evening to avoid wilting. Water with one to two tablespoons of a 12-12-12 fertilizer per gallon of water mixed in. Control weeds using shallow cultivation or mulch.

It is not recommended to water the plants 3 to 4 weeks before harvest. Too much water can cause the potatoes to split especially if conditions have been dry before the watering begins. Too much water or poorly drained soil prevents proper root formation and you may end up with long and stringy potatoes instead of short and plump ones. Sweet potatoes prefer hot, dry weather once the vines have covered the ground.

Sweet potatoes can be dug after the first frost in the fall. Using a spading fork or a shovel, dig down below the level of the ridge working closer to the plant and removing soil as you go. Be careful, their skins are tender and will bruise easily. Potatoes should be placed into clean storage containers. Allow them to dry and cure before removing clinging soil.

Sweet potatoes need to be cured before storing to allow wounds to heal and to improve the flavor. Sweet potatoes can be cured by placing them in a warm area. Optimal conditions would be 80 to 85 degrees and 85 to 90 percent relative humidity for 10 to 14 days and then stored in a cool (55 degrees) location. If curing room temperature is a bit cooler it may take up to three weeks for them to cure. Once the sweet potatoes are cured, wrap them in newspaper and store them in a cool, dark area where the temperature can be maintained at 55 to 60 degrees.

As always, Happy Gardening!

More information about gardening and related subjects is available online at  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.