Learn About Sweet Potatoes

Posted in: Other Vegetables
Learn About Sweet Potatoes

How To Sow    How To Grow    Tips    Common Pests    FAQ

How to Plant

  • Plant sweet potatoes as soon as you receive the bare roots, or “slips”, in spring, after all danger of frost has passed.
  • Do not be concerned if the plants look limp and the green tops do not look robust. If the roots are white and firm the plants are healthy and ready for planting. You can put them in a glass of water to help the roots absorb water and the greens should perk up.
  • Choose a sunny location with a loose, easily worked, well-drained soil. Sweet potatoes prefer a soil pH of 5.5 to 6.5. The ideal time to plant is late in the afternoon after the hottest part of the day, on a day that is not windy.
  • Plant sweet potatoes in ridges 8-12 inches high and 3 feet apart. Set the plants 10-18 inches apart.
  • When setting the plants in the ground do not cover the stem. Cover the roots and firm the soil. Water lightly.
  • If there is danger of frost cover the rows with row covers.
  • In areas with shorter seasons use black plastic mulches to warm the soil earlier in the season. If you use this method you may need to water more during periods of high heat during the growing season.

How to Grow

  • Cultivate around the plants to prevent weeds, and to prevent side roots from developing. Weeds compete with plants for water, space and nutrients. Cultivate carefully so as not to bruise or cut the young tubers forming just below the soil. Once plants get started their growth will tend to smother out many weeds and grasses.
  • Provide sweet potato plants with about ¾ inches of water weekly when they are young, and water them more as the plants mature. Do not water during the 2 weeks before harvest.
  • Many gardeners prefer not to fertilize because they feel not fertilizing improves the flavor, while others feel that fertilizing increases yields. If you choose to fertilize, side dress with a balanced fertilizer about six weeks after planting. Do not use excessive nitrogen.
  • Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.

Harvesting and Preserving Tips

  • Harvest small roots, or “baby bakers” anytime as desired, or harvest full-sized roots in the fall. Simply examine an average hill and dig the potatoes when they approach the desired size. Dig any remaining roots before frost.
  • When digging sweet potatoes be careful not to bruise them. Use a shovel or large pronged fork. With a loose row, pull the soil away with your hands.
  • After digging up your sweet potatoes, cure them in a warm, well ventilated location out of the sun for 8-10 days. This will help heal cuts and bruises and toughen the skin for winter storage.
  • Store sweet potatoes at 55°F at high humidity. Sweet potatoes can store for several months after being properly cured.
  • Eat sweet potatoes baked, mashed, candied, caramelized, deep-fried, stuffed or boiled.

Common Disease Problems

Black Rot: This bacterial disease thrives in warm and humid conditions and attacks underground fleshy storage roots as well as leaves. Infected roots develop a firm, black dry rot with lesions that enlarge. Black cankers form on the underground parts of the stem. Plants may be stunted, wilt and leaves may turn yellow and drop. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet. Control weeds where the disease can overwinter.

Dry Rot: This mostly affects sweet potatoes in storage, but can occasionally affect plants in the garden. It progresses from one end and causes the sweet potato to shrink or wrinkle. Affected tissue is light to dark brown externally and dark brown to black internally. Affected roots become mummified. Sprouts from infected seed roots may develop a reddish-brown to black decay at the base. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet. Control weeds where the disease can overwinter.

Fusarium Wilt:  Soil borne fungus causes yellowing of older leaves followed by wilting, leaf drop, and stunting or dying of the plant. Discoloration of the vascular tissues of the stem occurs earlier. Frequently, the symptoms are one-sided. They are more severe when soil moisture is low. The fungus persists in the soil for many years. Burpee Recommends: Practice crop rotation and plant resistant varieties.

Root Knot Nematodes: Microscopic worm-like pests that cause swellings (galls) to form on roots. Plants may wilt or appear stunted. This is a serious problem in many Southern states. Burpee Recommends: Do not plant into infested soil. Grow resistant varieties. Try planting ‘Nema-Gone’ marigolds around your plants.

Scurf: This fungus causes dark brown to black spots on the roots. The spots enlarge and coalesce. The lesions continue to enlarge in storage. The disease causes mostly cosmetic damage. Burpee Recommends: Rotate crops and remove all plant debris after harvest.

Common Pest and Cultural Problems

Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.

Cucumber Beetles: Beetles may be spotted, striped or banded and can be very harmful. Beetles are usually ¼ to ½ inch in size. Beetles start feeding as soon as they hatch and can kill or slow the growth of the plants. Beetle larva can bore through the roots of the plants. Beetles can also transmit diseases from plant to plant. Burpee Recommends: Knock off adults into a jar of soapy water and destroy them. Spade the soil to destroy dormant beetles before you plant. Use a row cover to prevent adults from feeding on young plants. Consult your Cooperative Extension Service for other insecticide recommendations.

Flea Beetles: These small hopping beetles feed on plant foliage and may spread diseases. Burpee Recommends: Rotate crops with plants in a different plant family. Use floating row covers to prevent damage to young foliage.

Sweet Potato Weevil: Weevil adults feed on any portion of the plant, but they prefer the roots. Larvae make feeding tunnels that begin just under the skin of the root. Adult exit holes in the root are about the size of a match stick. Sweet potato weevil infestations may be found in the field or in storage sheds, and in propagation beds. Burpee Recommends: When cultivating throw soil around the base of the vines to prevent adults from reaching the potatoes underground. Remove and destroy all plant debris. Remove and destroy volunteer sweet potatoes and morning glory vines, which serve as alternate hosts. Rotate crops. Check with your Cooperative Extension Service for pesticide recommendations

Wireworms: These insects live in the soil and kill seedlings by girdling their stems at the soil line; they bore into stems, roots and tubers. They may be found around the stems in the soil and are and ¼ to ¾ inch long, thin, yellow brown worms with a shiny skin. The adults are called click beetles, and are about 1/3 inch long, reddish brown with a hard shell. Burpee Recommends: Rotate crops. Check with your Cooperative Extension Service for pesticide recommendations which must be applied prior to planting.

Sweet Potato FAQs

How many sweet potatoes will I get from every slip? On average you should get about 2-4 pounds per slip.

Why did I not get any sweet potatoes? Sweet potatoes are a long season crop and the most tuber growth comes at the very end of the season. The absence of tubers or small tubers could indicate that your growing season was too short OR if leaves are repeatedly eaten or removed, this will reduce the size of the underground tuber OR your soil is not loose and friable enough.

My sweet potatoes arrived wilted. Are they dead? The tops will look wilted, but the roots should look white and firm. As long as the roots look good, the plants will grow.

My sweet potatoes have a hollow center in them, what happened? Hollow hearts can occur when uneven growth occurs during the formation of the tubers such as drought conditions followed by excessive rain. Mulch can help prevent uneven watering.

Are the colorful lime and purple sweet potato vines I see in window boxes and other planters edible? No these plants are ornamental.

October 29, 2021
©2023 W.Atlee Burpee & Co