Arbor

How to Grow Sweet Potatoes: Slips, Ridges, and Curing

Updated August 2026

Sweet potatoes start from slips, the sprouts pulled off a stored root, not from seed. Set them 3 to 4 inches deep, 8 to 12 inches apart in rows 3 feet wide, into a ridge mounded 8 to 12 inches high, and only once the soil under that ridge reaches 65°F. Count 95 to 120 days from there to harvest. Digging is not the finish line: a freshly pulled root is starchy and mild, and curing it warm and humid for about a week is what turns it sweet and heals the skin for storage.

How it works

Slips are the sprouts that grow off a stored sweet potato root, and they’re what goes in the ground — most gardeners buy them from a nursery or mail-order supplier rather than growing their own, per Penn State Extension. Growing your own takes six to eight weeks, bedding to planting (UMD), which is why it’s an early-spring commitment, not a planting-day decision.

The ridge matters as much as the slip. University of Maryland Extension recommends mounding soil 8 to 12 inches high and 12 inches wide before planting, because a ridge warms faster in spring than flat ground, drains better, gives roots room to bulk up, and makes digging easier at harvest. Clemson Cooperative Extension gives the same advice for a different reason in the Coastal Plain and Piedmont, where ridging is mainly about drainage.

Nitrogen is where sweet potatoes punish good intentions. University of Missouri Extension is blunt about it: excess nitrogen produces extensive vine growth and few actual sweet potatoes. All vine and no root is a nitrogen problem, not bad luck. University of Maryland Extension rates the crop a medium feeder, so work compost in before planting and side-dress nitrogen only once or twice, and only on light, sandy soils. That is a lighter hand than growing potatoes calls for, and carrying potato habits across is the usual way a gardener ends up with a bed of vines.

What to do

To grow your own, bed small to medium seed roots (about 1.5 inches across, free of blemishes) moist and warm at 75–85°F with 80–90% humidity until shoots emerge. Each root gives roughly three to five slips; pull them once they carry four or five leaves and a healthy root system, per Utah State Extension. A slip is rootless the moment it leaves its parent, so water it in right away.

Keep preplant nitrogen light. Without a soil test, Clemson’s default is 30 pounds of 5-10-10 per 1,000 square feet tilled in before planting, then 4 pounds per 100 feet of row before vines cover the bed. Missouri gets to the same place differently: P and K by soil test, then modest nitrogen three weeks after transplanting and again when vines begin running. Either way: light nitrogen, timed to when vines start running, never front-loaded.

With the bed fed, mound ridges 8 to 12 inches high and 12 inches wide, then wait for the soil under them to reach 65°F. That is the same threshold okra waits for, so the two can go in together. Set slips 3 to 4 inches deep in rows 3 feet apart with 8 to 12 inches between plants. Water them in well and keep them consistently moist while they root. Then taper off 3 to 4 weeks before you plan to dig — Utah State and Clemson both flag heavy rain or irrigation right before harvest, especially after a dry stretch, as what splits the roots.

If frost is forecast tonight, or the vines have already blackened, dig now whatever the root size — UMass Amherst is explicit that a hard frost turns harvest from planned to urgent. Short of that, most varieties are ready 95 to 120 days after transplanting, leaves turning slightly yellow as the sign, with a well-grown hill yielding around 2 pounds. Cut the vines off first, then loosen soil with a fork or spade and lift by hand. For general technique, see how to harvest vegetables.

Curing pays off, but UMD is upfront that it’s not strictly required — roots usually store successfully even when the week of curing is skipped. It’s worth doing anyway: several extension sources cluster around 82 to 86°F and 85 to 97% relative humidity for four days to a week (Missouri: 85°F, 90%, 4 to 6 days; UMass: 82–86°F, 90–97%, 4 to 7 days), which is what converts stored starches to sugars and lets a second skin grow over nicks from digging. Without a curing room, UMD’s fallback works: spread roots one layer deep on a porch, in a garage, or under any dry cover out of direct sun for about a week. If you log a note like “dug the sweet potatoes” in Arbor, it puts a curing task onto the next week’s list, since the step that makes them sweet is the easiest one to skip once the roots are already in a basket.

Zone and season notes

In short-season and cool-summer regions, the ridge does real work beyond drainage — it’s the fastest way to get soil past 65°F before a short window closes, and Utah State’s 8- to 10-inch raised bed serves the same end. In the Deep South the problem reverses: Clemson recommends ridging in the Coastal Plain and Piedmont mainly for drainage, since warmth is rarely the limiting factor.

Fall timing runs off soil temperature: roots keep growing until frost kills the leaves or soil falls consistently below 65°F, per UMass, whichever happens first. A second, lower number matters after harvest — chilling injury starts near 55°F, and below 50°F expect fungal decay, internal browning, and shriveling. Cold-zone gardeners work a much tighter digging window than the Gulf South, where soil rarely drops that low before vines are cut back on purpose.

After curing, move roots to storage around 55–60°F and 80–90% relative humidity, well above the 55°F line where chilling injury starts and well above refrigerator temperature. NC State’s commercial postharvest guide holds cured roots at a steady 55°F and 85–90% humidity for up to 13 months — a ceiling few home setups will match, but cool, humid, and steady is the direction to aim for.

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