When to Plant Sweet Potatoes: Soil Temperature, Slips and Dates by Frost

Sweet potatoes aren't grown from seed or seed pieces like regular potatoes. They're grown from slips, sprouts that grow from a stored root, and the plant is a tropical member of the morning glory family (UMD). That changes the timing completely: sweet potatoes go in weeks after regular potatoes, need a long warm season and must come out of the ground before cold weather damages the roots.

Step 1: wait for warm soil

The soil temperature matters more than the calendar. UMD and Clemson say to plant once the soil has warmed to 65°F; Texas A&M says the soil at planting depth should be over 65°F. Push a soil thermometer about 4 inches down in the late morning. Two ways to get there sooner:

• Ridges or raised rows. UMD notes that planting on ridges lets the soil warm faster in spring; Texas A&M suggests beds about 8 inches high.
• Black plastic. USU says planting through black plastic mulch allows planting up to ten days earlier than in uncovered soil.

Step 2: dates by last frost

The table uses Texas A&M's guidance: plant about two weeks after the last frost, within its window of 2 to 8 weeks after the frost-free date. Check the soil thermometer before the earliest date, especially after a cool spring. The slip column is for growing your own, about six weeks before planting (UMD).

Regional examples: Clemson lists May 1 to June 15 for South Carolina's Piedmont and April 15 to June 15 on the coast. UF/IFAS Gardening Solutions says Florida gardeners can plant any time after the threat of frost through the end of June. Clemson and Texas A&M both say a fall crop isn't recommended.

Step 3: buy slips or grow your own

UF/IFAS recommends starting with certified disease-free slips, and garden centers and online suppliers sell them in spring. Growing your own takes about six weeks from bedding the roots to planting (UMD):

• Bed method: UMD halves a root lengthwise, lays it cut side down in moist sand or potting mix, covers it with 2 inches more and keeps it at 75 to 85°F until shoots emerge. Illinois describes a hotbed at 70 to 80°F with slips ready in about six weeks.
• Jar method: Clemson describes suspending a root partly in water; sprouts appear in about two weeks, and the cut sprouts root in water in about ten days.
• Store roots: UMD notes roots bought at a market may be treated to stop sprouting, so wash them first, or use certified seed stock.

Step 4: the last planting date

Sweet potatoes need a long season. Texas A&M's table gives 100 to 130 days; USU says roots mature in four to five months; UMD gives 85 to 120 days. Texas A&M's rule is to plant at least 150 days before the soil temperature drops to 55°F in fall. Counting the variety's days back from your first fall frost gives the latest date, as below. Treat it as the last possible date and plant earlier where you can, because growth slows as fall nights cool.

Days to maturity from Utah State's variety list: Centennial and Georgia Jet 90 to 100 days, Beauregard 105 to 110, Vardaman (bush) and Bush Porto Rico 110, Carolina Bunch 110 to 120 and Jewel 120 to 135. In short-season northern gardens, pick the fastest variety you can find.

Planting, spacing and water

Harvest before the cold

Sweet potato roots are damaged by cold. USU says plants can be damaged by temperatures below 50°F, and Illinois suggests digging around the time of the first frost. Dig carefully to avoid bruising the roots.

• Cure them: Illinois says to cure freshly dug roots at about 85°F and 85% humidity for 10 to 14 days, then store them at about 55°F.
• Keep them out of the fridge: Clemson warns never to store sweet potatoes below 50°F or in the refrigerator.

Where sweet potatoes go in the garden

Give sweet potatoes a sunny spot with room to sprawl, next to other warm-season crops that go in after the frost. Despite the name, they aren't closely related to regular potatoes, which are planted weeks earlier; see when to plant potatoes. For other long-season, frost-tender crops, see when to plant pumpkins and when to plant melons.

Frequently asked questions

When should I plant sweet potato slips?

After your last spring frost, once the soil has warmed to about 65°F (UMD, Clemson, Texas A&M). Texas A&M suggests about two weeks after the last frost, within 2 to 8 weeks after the frost-free date.

What soil temperature do sweet potatoes need?

About 65°F at planting depth (Texas A&M, UMD, Clemson). Ridges and black plastic mulch help the soil warm sooner; USU says black plastic allows planting up to ten days earlier.

When should I start sweet potato slips?

About six weeks before your planting date (UMD, Illinois). Clemson describes a jar method in which sprouts appear in about two weeks and root in water in about ten days.

Is it too late to plant sweet potatoes in June?

Not always. Clemson lists planting through June 15 in South Carolina, and UF says Florida gardeners can plant through the end of June. In shorter seasons, count your variety's days to maturity back from your first fall frost.

How long do sweet potatoes take to grow?

Roughly 90 to 120 days for most varieties: UMD gives 85 to 120 days, USU four to five months and Texas A&M 100 to 130 days.

When should I dig sweet potatoes?

Before cold weather: USU says plants can be damaged below 50°F, and Illinois suggests digging around the first frost. Cure the roots warm and humid for 10 to 14 days, then store at about 55°F.