When to Plant Sweet Potatoes: Slip Dates by Frost and Zone

Plant sweet potato slips outdoors 3 to 6 weeks after frost danger has passed, on a day when the soil 4 inches (10 cm) down holds 65°F (18°C) or warmer. Across the North and Midwest that lands between mid-May and late June. The upper South plants in May and June, the Houston area from April through June, and South Florida and the Arizona low desert plant over many months.

The soil thermometer has the final say, not the calendar. Slips set into cold, wet ground can rot, and the survivors may sit for up to a month before they start to grow. At the other end of the season, the roots need 90 to 120 frost-free days to size up, so northern gardens also have to plant early enough to dig before fall cold returns.

Sweet potato planting dates by city

Planting opens in late March in Dallas-Fort Worth and not until mid-June in Fargo, and in every city the soil test decides the day.

Frost dates are medians from NOAA 1991–2020 climate normals for each city's main weather station; in half of years the last frost falls later than the date shown.

For the Midwest and Mountain cities, the table counts 3 to 6 weeks from each city's 1-in-10 last-frost date, the day after which a spring frost arrives only one year in ten, so the window opens about 5 to 6 weeks after the median shown. For a town in those regions, find your own 1-in-10 date, or add about 1½ to 3 weeks to your median, and count forward 3 to 6 weeks. Plant on the first day in that span when the soil passes the 65°F (18°C) test described below.

Fargo's window is short because its season is. A slip set out around June 13 has 109 days before the median first frost on September 30, and one set out on June 22 has 100, little more than the fastest varieties need. Plant through black plastic and pick one of the 90-day varieties. Denver's window leaves 101 to 122 days, enough for a 90- to 100-day variety planted promptly.

Boston's frost dates come from Logan Airport on the harbor and New York's from Central Park, so a garden in the suburbs or inland can run later. Plant there by the soil thermometer rather than a date. Farther north in New England the soil warms later still: in Durham, New Hampshire, ground under black plastic reaches 65°F (18°C) around June 1, and bare ground 1 to 2 weeks after that.

The upper South starts in May. West Tennessee plants May 1 to June 15 and East Tennessee May 15 to June 30, with Nashville between the two. Around Raleigh, slips can go in from May 1 until July 15. In the Georgia and South Carolina Piedmont, the soil reaches 70°F (21°C) in early May and planting runs to mid-June.

Texas's statewide guide plants 2 to 8 weeks after the median last frost, which gives Dallas-Fort Worth late March to early May; within that span, wait for 65°F (18°C) soil. Houston follows Harris County's own planting chart, which runs from April through June.

Around Seattle, slips go in under black plastic between mid-May and early July, depending on how quickly the site warms. In the Sacramento Valley, slips go out about mid-May, once the soil reaches 65 to 70°F (18–21°C).

Planting times by region

The later your soil warms, the later you plant: from February in central Florida to June in northern New England.

Dates are for setting slips in the garden; within any window, wait for a day when the soil is warm.

North and Northeast (Zones 3–6). Black plastic is close to essential here. Good yields on bare New England soil are hard to get, while raised beds covered with black plastic give bigger crops.

Midwest and Plains. Iowa plants from mid-May into early June, once frost is past and the soil is warm. A cold May pushes every date back; ridges and black plastic help here too, and the crop has to be dug before the first fall frost.

Mid-South and Southeast. Kentucky's planting season opens about three weeks later in the east than in the west and closes two weeks sooner, so use the dates for your end of the state. The sweet potato weevil is a serious pest across the South, so buy certified slips and move the crop to a different bed each year.

Texas and the Gulf Coast. Texas allows 100 to 130 days from planting to harvest. Around Houston, the county planting chart sets slips out from April through June, with the first week of April marginal.

Florida, the low desert and other frost-free areas. Frost dates do not apply in South Florida or the Arizona low desert, so let soil warmth and the season set the date instead.

California. Sweet potatoes crop well only in the warm parts of the state, such as the Sacramento Valley. Quarantine rules against the sweet potato weevil stop many mail-order nurseries from shipping slips into California, so check that a supplier can ship to you, or buy certified slips from a local garden center.

Pacific Northwest. West of the Cascades, plant from mid-May to early July as your site warms, through black plastic, and choose a 90-day variety. Oregon's own planting table does not recommend the crop for the coast or the western valleys. It lists sweet potatoes only for the Columbia and Snake River valleys, planted in May.

Intermountain West. In Utah, roots take 4 to 5 months to mature, longer than the 90 to 120 days most guides give. Plant on the first day after frost danger that the soil holds 65°F (18°C), and keep floating row cover on hand for cold snaps.

How to tell the soil is ready

The soil is ready when a thermometer pushed 4 inches (10 cm) into the bed reads 65°F (18°C) or more for 4 days in a row. No frost should remain in the forecast either.

Cold soil does real harm rather than just slowing things down. Cool or poorly drained ground can damage young sweet potato plants and rot the slips outright. Soil below 55°F (13°C) is harmful to the crop, and below 50°F (10°C) roots and plants suffer chilling injury.

Watch the air as well as the soil. Plants are damaged when the temperature drops below 50°F (10°C), so wait until forecast night lows stay above that. Some growers plant into soil of 60–65°F (16–18°C), but 65°F (18°C) is the safer figure, and Georgia gardeners wait for 70°F (21°C).

Warming the bed with black plastic

Black plastic mulch lengthens a short season by a few weeks. Through black plastic you can plant up to 10 days earlier than in bare soil. Lay it on the ridges once they are shaped so the soil has time to warm, then set slips through slits cut in the plastic. Raised ridges help too; their height is covered under planting depth and spacing.

Starting slips from roots

Bed roots 6 to 8 weeks before your planting date, which in most of the North falls a few weeks before your median last frost. Kentucky's calendar starts earlier, in mid-March, well ahead of its May and June planting.

Unlike ordinary potatoes, sweet potatoes are not grown from cut pieces of root. They are grown from slips, the leafy sprouts a root sends up, and both rooted and unrooted slips take hold in warm soil.

1. Choose the roots. Use firm, home-grown or organic roots of a named variety. Many grocery-store roots are treated to stop sprouting and carry no variety name.
2. Bed them 6 to 8 weeks ahead. Count back from your planting date, lay the roots on their sides in a tray, and cover them with 2 inches (5 cm) of moist sand or mix. Each root gives several slips.
3. Keep them warm and lit. Hold the tray at 75–80°F (24–27°C) under a plastic cover. Once sprouts appear, give them 14 to 16 hours of light a day.
4. Pull the slips. When sprouts are 4 to 6 inches (10–15 cm) long, pull them gently from the root. They need not have roots of their own to take in warm soil.
5. Hold slips warm until planting. Keep pulled slips above 60°F (16°C) until they go into the garden, since slips are as sensitive to cold as the growing plants.

Buying certified disease-free slips skips all of this and keeps weevils and disease out of the garden. If you order by mail, pick a ship date that lands inside your planting window.

Planting depth and spacing

Set each slip 3 to 4 inches (8–10 cm) deep, 12 inches (30 cm) apart, on ridges in rows 3 to 4 feet (90–120 cm) apart.

Build ridges 8 to 12 inches (20–30 cm) high before planting. A ridge warms sooner in spring and drains better, which matters for a crop that rots in cold, wet ground. Bury 2 to 4 leaf joints (nodes) on each slip, because roots form at the buried nodes, and leave the growing tip and top leaves above the soil. Some guides plant as deep as 5 inches (13 cm); the aim in every case is buried nodes and exposed leaves.

Spacing runs from 8 to 18 inches (20–45 cm) in different guides, with 12 inches (30 cm) the common choice for sweet potato plants.

Water each slip in well. On hot, windy days, plant in the late afternoon or under cloud so the slips do not wilt before they root, and keep the soil evenly moist while they take hold.

Choose light, well-drained soil, ideally a sandy loam. Heavy clay gives misshapen roots, and where your ground is heavy, a raised bed helps with both drainage and warmth. Go easy on feeding: too much nitrogen fertilizer or heavy dressings of fresh manure produce long, spindly roots and a mass of vines.

As the vines run, they root wherever their joints touch soil, and those extra roots divert growth from the main crop. Lift and move the vines now and then to stop them taking hold. Deer will graze the foliage to the ground, so fence the bed where they visit; voles feed on the roots underground.

Varieties that change the timing

Days to maturity run from about 90 for Mahon Yam and Centennial to 120 or more for Jewel, so in a short season the variety matters as much as the planting date.

Days count from setting slips in the garden. Guides disagree by 10 to 20 days for some varieties, so plan on the longer figure in cool regions.

In Zones 3 to 6, choose a 90- to 100-day variety such as Mahon Yam, Centennial or Georgia Jet, and save the fastest for a planting late in the window. Jewel, at 120 to 135 days, and Murasaki, at up to 120, belong where the season is long.

Bush types such as Vardaman and Bush Porto Rico suit small gardens where a vining sweet potato would spill into the paths, though Vardaman gives smaller roots and a lower yield.

What happens if you plant too early or too late

Planted too early, slips rot or stall in cold soil. Planted too late, the season ends before the roots reach full size.

An early planting rarely saves time. Sweet potatoes do little until the soil reaches 65°F (18°C), and in cool, overcast weather in central Maine new plants can take up to a month to start growing. Roots that do form in chilled soil can carry chilling injury, which shows up later as off flavor.

A late planting runs out of warmth before the roots fill out, and cooling soil at the end of the season lowers their quality even before frost arrives. In the North, the roots should be out of the ground before the soil drops below 60°F (16°C). If you are planting late, choose a 90-day variety.

If a late frost threatens new slips

Cover the rows with floating row cover in the evening before a cold night and take it off the next morning. Use the cover for any night forecast below 50°F (10°C), not only for frost, because that much cold already damages young plants.

Harvest, curing and storage

Dig sweet potatoes when the roots reach a useful size, before the first fall frost, then cure them warm and store them cool.

Check one plant 80 to 85 days after planting. The crop is ready when about a third of the roots are wider than 3.5 inches (9 cm), or when most weigh 6 to 8 ounces (170–230 g). Roots left too long can split. Cut back watering 2 to 4 weeks before digging to avoid cracked roots. Lift them with a spading fork pushed in 8 to 10 inches (20–25 cm) from the crown, so the tines miss the roots.

If frost blackens the vines before you dig, harvest at once or cut the vines away at soil level, because decay moves from the dead vines into the roots. Expect around 6 to 15 pounds (3–7 kg) from a 10-foot (3 m) row.

Cure freshly dug roots at 80–85°F (27–29°C) with 85–90% humidity for about a week. Little curing happens below 70°F (21°C), and in an ordinary warm room it takes about two weeks. Skipped or rushed curing leaves roots less sweet and more prone to rot.

After curing, store the roots at 55–60°F (13–16°C) and about 85% humidity. Wait 3 to 4 weeks before eating them: sugar content can more than double in the first three weeks of storage.

The cleared bed is free for a fall crop; see garlic planting times for what can follow. To line up slip-starting and planting dates with the rest of your warm-season crops, including tomato planting times and vegetable planting dates, add them to Sow's garden calendar.