When to Plant Sweet Potatoes

The two conditions: no frost and warm soil

Sweet potatoes are tropical plants and get no benefit from an early start. Two conditions have to be met before slips go in.

1. The frost risk has passed. Texas A&M’s rule is to wait 2 weeks after the average last frost. Clemson says to plant well after the last chance of frost.
2. The soil is warm. Clemson, Texas A&M and Penn State all want soil above 65°F at planting depth. UGA sets it at 70°F.

Air temperature matters too. Utah State notes that plants can be damaged below 50°F. In most years soil temperature is what holds planting back, because it lags behind air temperature in spring. Use the dates for your zone above as the earliest likely window, then check the soil 3 to 4 inches down before planting.

Why waiting pays off

Penn State describes sweet potatoes as highly sensitive to cold and advises against planting close to a frost event, early or late in the season. Texas A&M notes a second weak point: newly set slips are extremely sensitive to drought during their first month. Planting into warm soil and keeping it evenly moist through those first weeks gives slips the best start.

Count backward from fall

The other end of the season is just as important. Most varieties need 90 to 120 days from planting to harvest (Clemson, UGA), and the roots should be dug before cold soil lowers their quality. Texas A&M frames it as a window. Plant when soil tops 65°F in spring, and at least 150 days before fall soil is expected to cool to 55°F.

In practice, count back from the first fall frost date for your zone above:

• Long seasons (most of the South): You have room to wait for truly warm soil. Clemson’s South Carolina planting window, for example, spans about two months.
• Short seasons (northern tier): Plant as soon as the soil reaches temperature, and choose the earliest variety you can find. NDSU suggests ‘Beauregard’, ‘Covington’ or ‘Georgia Jet’ because later varieties may not mature before frost.

Timing your slips

If you grow your own slips, start them early enough to be ready on planting day:

• Water jar (Clemson): Sprouts appear in about 2 weeks, and once twisted off they root in water in about 10 more days. That comes to roughly 3½ weeks.
• Hotbed (Utah State): Roots bedded in sand at 70 to 80°F give slips 6 to 8 inches tall in about 6 weeks.
• Indoors (Penn State): Sprout disease-free roots at 75 to 85°F and high humidity, starting several weeks before outdoor planting.

Slips that are ready before the soil is can be held in water or potted into containers until planting (Clemson). Bought slips should go in soon after they arrive. NDSU warns that shipped slips often show up wilted and suffer shock.

Getting more season in cold regions

Northern gardeners can buy time by warming the soil. Utah State plants through black plastic mulch up to 10 days earlier than in bare soil and uses floating row covers for frost protection. NDSU recommends a raised bed covered with black plastic, plus row covers for a few weeks after planting. Penn State recommends both for Pennsylvania, where the frost-free season typically runs 130 to 170 days.

No fall crop, except in the tropics

Sweet potatoes are a single summer crop across most of the country. Clemson does not recommend fall planting in South Carolina. Where frost is rare, the window is much wider. UF/IFAS gives North and Central Florida a planting season stretching from late winter or early spring into early summer. In South Florida it covers most of the year. University of Arizona’s calendar for the Phoenix-area low desert runs slip planting from spring into early summer. The dates for your zone above reflect these regional windows.