How to Grow Sweet Potatoes: Slips, Planting, Harvest

Sweet potatoes grow from slips, not seed: start the slips indoors 6–8 weeks ahead, plant them outside three to four weeks after your last frost once the soil is warm, and dig the roots 90 to 120 days later. They are a long-season, warm-soil crop, and the single biggest mistake is planting into cold ground. Penn State says the plants are very sensitive to cool soil, and that soil colder than 50°F (10°C) leads to root rot. Everything below comes from Penn State, Clemson and UGA extension; where they differ you get both numbers.

Water

Moderate

Days to harvest

90–120 days from planting slips

Origin

The Americas

Container friendly

Yes

Planting depth

3–4 in. (Clemson) · 6 in. (Penn State)

Spacing

8–12 in. apart, rows 3 ft (Clemson)

Sun

Not stated by our sources

Season

Warm soil, 65–70°F+ · tender to frost

USDA zones

Not stated by our sources

When to plant sweet potatoes

Two numbers matter: soil temperature and the frost-free date. Clemson says the soil should be above 65°F (18°C) before planting, and Penn State also uses 65°F. UGA says the soil should reach 70°F (21°C). Penn State says to plant three to four weeks after the frost-free date, which in most of Pennsylvania falls at the end of May or the beginning of June. Your county extension office or the National Weather Service site gives your frost-free date.

Slips themselves are started well before that. Penn State says to begin six to eight weeks before planting, and our sweet potato slips guide walks through the method.

Why slips, and where to get them

Sweet potatoes are not grown like potatoes or from seed packets. Penn State says slips are sprouts on sweet potatoes from the previous year’s crop. You can buy slips by mail order, at nurseries or at farmers’ markets, and Penn State says slips from reputable nurseries will be free of disease. You can also grow your own from a previous harvest or even from store-bought sweet potatoes, as a fun project or if you need a lot of slips. Each sweet potato gives three to five slips (Penn State).

What the sources disagree on

Three university sources cover sweet potatoes and they differ on several numbers. None of the ranges is wrong; they reflect different regions and methods.

The water gap is the widest. Penn State’s half inch is for a mulched, ridged bed in a cooler climate, which is our reading, not a stated reason. When in doubt, aim for even moisture and avoid both drought and standing water, since waterlogged soil rots the roots (Penn State).

Vines, leaves and space

Sweet potatoes are sprawlers. Penn State says most varieties root wherever the stems touch the ground, and that vines can reach 20 ft (6 m). It also says the young leaves and shoots are edible, and that you can grow them vertically on a sturdy trellis, in the garden or in large pots, to save space and make leaf harvesting easier. Sweet potatoes are naturally crawlers, not climbers, so you weave the vines through the trellis yourself. If you grow in the ground only for the roots, Penn State advises against pruning, as it can cause the roots to sprout.

Bush types such as Porto Rico and Vardaman spread much less, about 2 ft (60 cm) per plant (Penn State).

A season with sweet potatoes

1. 6–8 weeks before planting: start slips indoors at about 75°F (24°C) (Penn State).
2. Soil above 65°F, 3–4 weeks after the last frost: plant slips on ridges and water daily for two weeks.
3. Summer: vines cover the soil and shade weeds. Clemson wants at least 1 in. of water a week.
4. 3–4 weeks before harvest: stop watering to prevent splitting (UGA).
5. 90–120 days after planting: harvest before the first killing frost, then cure.

Sweet potato varieties

Clemson lists three varieties with days to maturity. Our sources give no further flavor or color detail except as noted.

How to plant sweet potatoes

1. Wait for warm soil. Above 65°F (18°C) per Clemson and Penn State, 70°F (21°C) per UGA, and three to four weeks after the frost-free date (Penn State).
2. Loosen the bed. Penn State says sweet potatoes need loose, well-drained soil, and that compacted, waterlogged soil makes them rot. Adding 1–2 in. (2.5–5 cm) of compost loosens it. Soil too rich in nitrogen gives many leaves but few potatoes.
3. Build ridges. Penn State makes long ridges 8–12 in. (20–30 cm) high and 12 in. wide, rows 3 ft (0.9 m) apart. Clemson also says rows 3 ft apart.
4. Plant the slips. Clemson says 8–12 in. (20–30 cm) apart in the row at 3–4 in. deep. Penn State says about a foot apart on top of the ridge, 6 in. deep with at least two nodes underground. UGA says a hole 4–6 in. deep. Slips do not need roots to be planted (Penn State).
5. Water daily at first. Penn State says to water newly planted slips every day for the first two weeks.

Sweet potato care

Sweet potatoes can also be grown in containers; see our sweet potatoes in containers guide.

Common sweet potato problems

Penn State adds that voles, mice and deer can be a problem, and that raised beds or large containers keep rodents out.

Harvesting and curing sweet potatoes

Penn State, Clemson and UGA say roots need 90 to 120 days from planting. Harvest when the leaves begin to turn yellow, before a light frost (Penn State), or when 30 percent of the roots are larger than 3½ in. (9 cm) across (Clemson). The roots must come out before the first killing frost.

Cure them before storing. Clemson says the best conditions are 85°F (29°C) and 90 percent humidity for one week; Penn State says 80–85°F for two weeks. Store at 50–60°F (10–16°C), never below 50°F and never in the refrigerator (Clemson). The sweet potato harvesting guide has the full sequence.

Sweet potatoes belong to the warm-soil crowd. Okra waits for the same 65°F soil; see our okra growing guide.