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

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. Feed them well and you get a thicket of vine with almost nothing under it — all vine and no root is a nitrogen problem. These are medium feeders, so work compost in before planting, then side-dress with fertilizer (scattered alongside the row) 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

Growing your own slips

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.

Feeding, ridging, and setting slips

Keep preplant nitrogen light. Without a soil test, Clemson’s default works out to about a pound of 5-10-10 fertilizer across a 4×8 bed (30 pounds per 1,000 square feet), tilled in before planting. Wait for the vines to start running before feeding again, then scatter roughly 5 ounces of the same 5-10-10 fertilizer along an 8-foot row (4 pounds per 100 feet of row) before they close over the bed. Front-loading it all at planting instead results in lots of vines and few potatoes.

After fertilizing the bed, mound ridges 8 to 12 inches high and 12 inches wide in a spot that gets full sun, 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. At that row spacing a 4×8 bed holds one ridge down its length, which comes to 8 to 12 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.

Digging and curing

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. Do it anyway. Four days to a week at 82 to 86°F, with humidity at 90% or above, is what converts stored starches to sugars and lets a second skin grow over nicks from digging. Without a curing room, spread the roots one layer deep for about a week on a covered porch or in a garage, whichever spot is warmest and keeps off rain and direct sun without drying the air out. That gets you a partial cure rather than the whole job, which is the argument for hunting out the warm corner instead of the convenient one. If you log a note like “dug the sweet potatoes” in Arbor, it recommends a curing task for 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.

Roots keep growing until frost kills the leaves or the soil falls consistently below 65°F, whichever comes first.

A second, lower number matters after harvest. Chilling injury starts at about 55°F, and it shows up as shriveling and sunken dark patches on the skin, with blackening inside when you cut one open. 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 at 55–60°F and 85 to 90% relative humidity. The bottom of that band is the chilling threshold itself, so 55°F is a floor to hold rather than a number to aim at. A shelf that sits near 60°F beats a cellar that dips under 55 on cold nights, and a refrigerator is colder than either and ruins them outright. Commercial storage holds cured roots at a steady 55°F, ventilated and undisturbed, for as long as 13 months.