Quantcast
Sweet Potatoes: How to Plant, Grow, and Harvest Sweet Potatoes | The Old Farmer's Almanac

Sweet Potatoes

Photo Credit
Bonnie Taylor Barry/Shutterstock
Botanical Name
Ipomoea batatas
Plant Type
Sun Exposure
Soil pH
Bloom Time
Flower Color
No content available.
Subhead

How to Plant, Grow, and Harvest Sweet Potatoes

The Editors
Print Friendly and PDF

Just a few sweet potato plants can produce a generous harvest of this nutritious, sweet-tasting root vegetable. More commonly grown in the South because they require warm weather, northern regions can have success with select varieties. Here’s how to plant, care for, and harvest sweet potatoes—plus, discover best varieties.

About Sweet Potatoes

The sweet potato is a tropical plant and a member of the morning glory family. Compare a sweet potato vine’s foliage and flowers to those of a morning glory and you’ll see the family resemblance! Despite their name, they are not related to potatoes, which are in the nightshade family. Another difference between sweet potatoes and “standard” potatoes is that the edible portion of the sweet potato is a tuberous root, not a true tuber (which are technically modified plant stems). 

This root vegetable has deep-orange flesh and a coppery skin jacket. Sweet potatoes are commonly served cooked in mashed form, or roasted whole. Or, they may be used as a pie filling.

Sweet potatoes. Photo Credit: Brent Hofacker/ShutterstockPhoto Credit: Brent Hofacker/Shutterstock

This tropical crop needs at least four months of warm weather and warm soil, but they are drought- and heat-tolerant and have few pests or diseases. Although traditionally more of a Southern crop, there are many short-season varieties of sweet potato today. They will grow in the North (even parts of Canada!), when grown in sandy soil or raised beds that are mulched with black plastic to keep the soil warm.

Sweet Potato Slips

Note that sweet potatoes are not grown from seed. Instead, they’re grown from slips, which are sprouts grown from existing sweet potatoes. Slips are often available at local garden centers, nurseries, from local farmers (such as farmers markets), or from mail-order companies. Or, you can start your own (see how below).

Before ordering slips, make sure that you have a long enough growing season to actually grow sweet potatoes. Most varieties will take about 90 to 120 days to mature. See your frost dates and length of growing season. Also, make sure you time your order with your planting dates in mind!

Planting

Choose a sunny spot with well-drained soil. Sweet potatoes aren’t too picky, but they do prefer soil on the sandier side. They need plenty of air space in the soil for roots to reach down. If your soil is clay, rocky, or compacted, consider growing in raised beds.

Add compost as well as perlite and/or coconut coir to the growing area to build fertile, loamy soil down to 8 to 10 inches. Avoid adding animal manure, including pelleted chicken manure; it can result in spindly and/or stained roots. Also avoid heavy nitrogen fertilizers, which produce lush leaf growth at the expense of the edible roots!

When to Plant Sweet Potatoes

  • Plant slips outdoors 3 to 4 weeks after your last spring frost or once the soil has warmed to at least 65°F (18°C). Nighttime temperatures should be at least 55°F (13°C). The trick is to plant them early enough for them to have time to mature fully, but not so early that they get killed by a late spring frost.
  • Be sure to protect young sweet potatoes from any late frosts or cool nights (lower than 55°F/13°C), as they are very tender. Cover them with plastic milk jugs or use row covers, removing the covers during the day.
  • If you ordered slips from a mail-order source, unpack them right away. Stick the roots in water for a day or so and they’ll perk up. Plant them as soon as conditions are right.

planting_sweet_potato_lex20_gettyimages_full_width.jpgImage: Sweet potatoes are grown from slips—sprouts grown from existing potatoes! Credit: Lex20/Getty Images.

How to Grow Your Own Sweet Potato Slips

You can start your own slips instead of buying them, but it’s more work. Here’s how:

  • About 8 weeks before your last spring frost date, look for unblemished, smooth, organic sweet potatoes at the store or farmers market. Be sure to ask about the variety and check that it’s one that you want to grow.
  • Place the whole sweet potatoes in pots or bins that contain at least 3 inches of light, organic, well-draining soil. Leave an inch or two of space between each sweet potato.
  • Lightly cover with a few inches of additional soil. Water now and as needed to keep soil damp but not soggy.
  • Maintain the soil and the room at 75°F to 80°F in sunlight or under artificial lights. Use a heating mat if necessary; sweet potatoes respond well to warm temperatures.
  • Soon, slips (shoots) will emerge from the soil.
  • After about 6 to 8 weeks, the slips should be between 6 and 12 inches long, with a number of leaves and roots.
  • Remove the slips from the sweet potatoes, with roots attached. (If no roots have formed on the slip itself, remove the slip and place it in water; roots should appear in 1 to 2 weeks.)
  • If it is still too soon to plant outdoors, stand the slips in potting mix or sand and keep moist until the right planting time (3 to 4 weeks after last frost).
  • Harden off the slips (before planting outdoors) for 1 to 2 weeks by exposing them to filtered sunlight outdoors during the day.

How to Plant Sweet Potatoes

  • Create raised mounds 6 to 8 inches tall and about 12 inches wide. 
  • Plan 3 feet between mounds so that there is enough space for vines to run. 
  • Plant the slips on a warm, overcast day, when the soil temperature has reached 60°F (15°C). 
  • Break off the lower leaves, leaving only the top ones.
  • Set the slips deep enough to cover the roots and the stem up to the leaves. Sweet potatoes will form on the nodes.
  • Water with a high-phosphorus liquid fertilizer, then water generously for 7 to 10 days to make sure that the plants root well.

See more tips for growing sweet potatoes.

Growing
  • Side-dress the sweet potato plants 3 to 4 weeks after transplanting with 5-10-10 fertilizer. If you have sandy soil, use more.
  • Weed the sweet potato beds regularly starting 2 weeks after planting.
  • Avoid deep digging with a hoe or other tool that disturbs the delicate feeder roots.
  • Water regularly, especially during mid-summer. Deep watering in hot, dry periods will help to increase yields.
  • Do not prune sweet potato vines; they should be vigorous.
  • Late in the season, reduce watering to avoid cracking of the sweet’s skin—a problem in storage.

sweet_potato_gettyimages_full_width.jpgImage: We thinks sweet potatoes make a nice ground cover, too! Credit: Getty Images.

Harvesting
  • You can start digging up the roots as soon as they are big enough for a meal.
  • Harvest when the leaves and ends of the vines have started turning yellow or about 100 days from planting.

  • Loosen the soil around each plant (18 inches around, 4 to 6 inches deep) to avoid injuring the roots. Cut away some of the vines.
  • Pull up the plant’s primary crown and dig up the roots by hand. Handle the sweet potatoes carefully, as they bruise easily. 
  • Shake off any excess dirt; do not wash the roots.
  • Complete harvesting by the first fall frost.

sweet-potatoes-tubers_full_width.jpg

How to Cure and Store Sweet Potatoes

  • Curing sweet potatoes gives them that sweet taste and also allows a second skin to form over scratches and bruises.
  • Handle sweet potatoes carefully; they bruise easily.
  • To cure, store roots in a warm place (about 80°F) at high humidity (about 90%) for 10 to 14 days. A table outside in a shady spot works well. Arrange sweet potatoes so that they are not touching.
  • After curing, discard bruised sweet potatoes, then wrap each one in newspaper.
  • Carefully pack in a wooden box or basket. Store in a root cellar, basement, or the like with a high humidity at 55° to 60°F.
  • The roots should last in storage for about 6 months.
Wit and Wisdom
  • Sweet potatoes are a very healthy root vegetable, and they provide many benefits. Here’s why you should eat sweet potatoes.
  • They were used in folk remedies to treat asthma, night blindness, and diarrhea.
  • Sweet potatoes are not yams, which are related to grasses and lilies. They’re also not related to regular white potatoes, which belong to the nightshade family, versus the morning glory family. As mentioned above, potatoes’ edible portion is a true tuber, while sweet potatoes produce tuberous roots.
Pests/Diseases

Sweet Potato Pests and Diseases

Pest/Disease Type Symptoms Control/Prevention
Flea beetles Insect Numerous tiny holes in leaves Use row covers; mulch heavily; add native plants to invite beneficial insects
Fusarium wilt (stem rot) Fungus Yellow/puckered leaves; older leaves drop; wilting vines; plants eventually die; stems under-/near ground may appear slightly blue; stem cross section reveals brown/purple/black discoloration, especially near ground Destroy infected plants; choose certified, disease-free slips and resistant varieties; rotate crops
Sweet potato scurf Fungus Skin-deep, dark brown/black spots or blotches on root tuber that may enlarge in storage; roots may shrivel; reduced shelf life Choose certified disease-free plants or use vine cuttings or sprouts cut at least 1 inch above soil line; disinfect tools and storage containers; rotate crops
White rust Fungus Chalk-white blisters mainly on leaf undersides; small, yellow-green spots or blisters, sometimes in circular arrangement, on upper leaf surfaces; possible distortion or galls; flowers/stems may also be infected Destroy infected plants; choose resistant varieties; weed; destroy crop residue; rotate crops
Whiteflies Insect Sticky “honeydew” (excrement); sooty, black mold; yellow/ silver areas on leaves; wilted/stunted plants; distortion; adults fly if disturbed; some species transmit viruses Remove infested leaves/plants; use handheld vacuum to remove pests; spray water on leaf undersides in morning/evening to knock off pests; monitor adults with yellow sticky traps; spray with insecticidal soap; invite beneficial insects and hummingbirds with native plants; weed; use reflective mulch
Cooking Notes

Relatively low in calories, sweet potatoes are very nutritious, a top source of beta-carotene, and also contain some protein, calcium, iron, vitamins A and C and other minerals.  They can be stored longer than winter squash.

To the cook, sweet potatoes are easier than pie (or sweet potato pie!).

  • They can simply be scrubbed, poked with a fork in a few places, and baked at 400°F for 35 minutes to one hour, until they give a bit when you squeeze them in your pot-holder-protected hand.
  • In the microwave, a whole sweet potato baked on high should be ready in 4 to 6 minutes. It may still feel firm when done; let it stand about 5 minutes to soften.
  • Sweet potatoes can also be steamed whole (cleaned and unpeeled) for about 40 minutes or until tender, or cooked whole (cleaned and unpeeled) in boiling salted water for about 35 minutes. (Boiling reduces the flavor considerably.)
  • Immerse cut raw sweet potatoes in water until you’re ready to cook them; they will darken otherwise.

As a general rule, don’t substitute sweet potatoes for regular potatoes in recipes; the two aren’t related. Sweet potatoes don’t hold together the way potatoes do, and their strong flavor can overwhelm a dish meant for a milder potato taste. Sweet potatoes are also not related to yams. But they make a fine substitute for pumpkin, especially in desserts.

Check out our ten best sweet potato recipes!

vegetable_gardeners_handbook_spring_ad.png