Sweet Potato

Sweet potatoes (Ipomoea batatas) are not related to potatoes. They’re a member of the morning glory family (Convolvulaceae), and the biology of propagating them reflects that - you don’t plant tubers or seeds, you plant slips, which are rooted stem cuttings grown from a stored sweet potato. Once you understand how slips work, the year-over-year economics of growing sweet potatoes become substantially better than almost any other vegetable crop.

Year one: you buy slips at $3–$6 per bunch of 5–12 slips, or you buy one sweet potato from the grocery store and grow your own. Year two: you save a few roots, grow slips from them in early spring, and plant for near-zero input cost. The crop is perennial in zones 9–11; in cooler zones it’s an annual, but the slip propagation cycle means your seed cost in subsequent years is the cost of a little heat mat time and some water.

Slips: how the propagation actually works

A sweet potato slip is a stem cutting taken from a sprouting root. Six to eight weeks before your last frost date, take a sweet potato root and suspend it half-submerged in a jar of water in a warm (75–80°F) location. Shoots will emerge from the root. When shoots are 4–6 inches long with developing root nodes, twist them off and place them in water until roots are 1–2 inches long, then transplant. One sweet potato root can produce 10–20 slips (University of Georgia Extension, Sweet Potato Production, Bulletin 1338, 2020).

Commercially produced slips are available from seed companies and are certified disease-free. For first-year growers unfamiliar with the crop, purchased slips are reliable. After year one, save a few good-looking roots and grow your own.

Variety selection

Beauregard is the commercial standard - disease-resistant, produces in 90–100 days, orange flesh, widely available as slips. Consistent and predictable.

Covington is the dominant commercial variety in North Carolina production. Better skin appearance and longer storage life than Beauregard.

Jewel and Garnet are common storage types with good flavor and 4–5 month storage life.

Japanese/Korean white-flesh types (Murasaki, O’Henry) command $3–$5/lb at Asian specialty markets and farm stands (USDA AMS Specialty Crop Market News, 2023). If you have access to those markets, white-flesh varieties shift the ROI math considerably.

Vardaman is a compact bush type that works for small spaces and containers - most sweet potato vines spread 4–6 feet in every direction.

The ROI case

Slips from a retailer run $0.50–$0.75 each. At 4 lb average yield per slip (under good conditions) and $1.75/lb retail (USDA ERS, Vegetables and Pulses Yearbook, 2023), each slip returns $7. The seed cost per slip is $0.50–$0.75. That’s a 9:1 to 14:1 return by value in year one.

In year two, if you grew your own slips from saved roots, your input cost drops to electricity for the heat mat and the cost of the jar on your windowsill. The return per square foot over a multi-year planting cycle is hard to beat.

Growing requirements

Sweet potatoes are serious heat lovers. They’re native to tropical South America and perform accordingly. Soil temperature must be above 60°F before transplanting - below that, vines stall and root development is poor. Most gardeners in zones 5–7 transplant slips 3–4 weeks after last frost when soil has had time to warm (Clemson Extension, Sweet Potatoes, HGIC 1322, 2021).

In cool-summer climates (Pacific Northwest, upper Midwest), short-season varieties like ‘Vardaman’ (90 days) and the use of black plastic mulch to preheat soil can make the difference between a harvest and a failure. Without soil warming, vines grow but don’t produce meaningful roots before frost.

Soil pH of 5.5–6.5. Sweet potatoes prefer slightly acidic, loose, well-drained soil. Sandy loam is ideal. Heavy clay prevents root expansion and produces misshapen, cracked tubers. If your soil is heavy, growing in raised beds or mounded rows improves the outcome significantly.

Once established (2–3 weeks after transplanting), sweet potato vines are genuinely drought-tolerant - more so than almost any other common vegetable crop. They evolved in a seasonally dry environment. Overwatering established plants is a more common mistake than underwatering; wet soil encourages root rot. Water once per week during the main growing season; reduce further once vines are dense and covering the soil.

Nitrogen is counterproductive in sweet potatoes. Excess nitrogen produces lush vine growth and tiny roots. If you’ve amended with heavy compost or added nitrogen fertilizer, you may end up with beautiful vines and a poor harvest. Apply compost sparingly and skip nitrogen-heavy fertilizers entirely after transplanting.

What goes wrong

Sweet potato weevil (Cylas formicarius) is the most serious pest where it’s established (primarily in the Gulf States). The adult is a small blue-black and red weevil; larvae bore through vines and into storage roots, making them inedible. There is no effective chemical control for established infestations. Prevention: use certified slip stock from disease-free sources, rotate crops, destroy all crop debris at season end, and don’t move soil or plant material between sites.

Fusarium wilt (Fusarium oxysporum f. sp. batatas) causes yellowing, wilting, and death of vines. Infected roots show internal brown discoloration. Resistant varieties (Beauregard, Covington) are the primary management tool. Don’t replant in an infected bed for several years.

Scurf (Monilochaetes infuscans) is a soilborne fungus that causes dark, scurfy patches on root skin. It’s cosmetic but reduces marketability. Certified slip stock and crop rotation prevent it from building up.

Wireworms (click beetle larvae, family Elateridae) bore into roots. Same management as with potatoes: avoid beds recently converted from lawn, rotate away from problem areas.

Harvest and storage

Harvest before the first killing frost. Frost-damaged sweet potato roots rot quickly in storage. The standard timing: 90–120 days after transplanting. Check root size by gently digging alongside a plant with a fork to expose a root without pulling the vine.

Harvest carefully - sweet potato roots bruise easily, and any damage creates an entry point for storage rot. Dig with a broad fork, not a spade. Work slowly.

Cure immediately after harvest: 85–90°F with 85–90% relative humidity for 4–7 days. This critical step heals wounds, sets the skin, and converts starches to sugars - it’s what makes a freshly dug sweet potato sweet rather than starchy (North Carolina State Extension, Sweetpotato Storage, AG-09, 2019). Without proper curing, the roots store poorly and don’t develop full flavor.

After curing, store at 55–60°F in moderate humidity. Do not refrigerate - temperatures below 50°F cause chilling injury and produce an off-flavor. Properly cured Beauregard and Covington types store 4–6 months. Specialty types vary.

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Related crops: Arugula, Winter Squash

Related reading: Beginner Homestead Crops - where sweet potatoes fit in a first-year homestead growing plan