Sweet Potato

Sweet potato is the vegetable that rewards you most for understanding what it actually is: not a potato, not a root vegetable in the conventional sense, but a tropical morning glory that happens to store energy in its tuberous roots. It is grown from rooted stem cuttings called slips, not from seed or from the tubers themselves — which means sourcing planting material is the first thing to figure out, usually in early spring before the catalogs sell out.

Plant slips three weeks after your last frost date, when the soil has warmed to at least 65°F. Sweet potato vines planted into cool soil may survive, but they stall for weeks and never quite catch up. Space slips 12 to 18 inches apart in loose, well-drained soil. The most common mistake is amending the bed too heavily with nitrogen fertilizer: sweet potatoes grown in nitrogen-rich soil tend to push vigorous, lush vines with few storage roots. Go easy on the compost and skip the fertilizer entirely unless the soil is genuinely poor.

Once the vines are established, they need very little attention. Water during dry spells in the first few weeks after transplanting; after that, the plants are moderately drought-tolerant and deep-rooted. The vines will sprawl across a wide area — in a good season, one plant can cover four to six square feet of ground. Do not be alarmed by this. The vine is doing its job. Some gardeners lift the vines periodically to prevent adventitious roots from forming where stems touch the soil; this may slightly improve tuber size but is not strictly necessary.

The harvest window is the part most new growers get wrong, and in two different directions. Pulling too early — before about 90 to 100 days from transplanting — means small, not-yet-swelled tubers. But waiting too long into fall risks frost damage to the tops, which can rapidly transmit rot down into the roots. Dig when the vines have begun to yellow slightly, or about two weeks after the first light frost kills the tops — whichever comes first. Dig carefully with a fork, starting at the edge of the hill, not straight down into it.

Curing is not optional. Freshly dug sweet potatoes are not ready to eat and do not taste sweet. They need to be held at 85°F with 90% humidity for 7 to 10 days, which converts starches to sugars and heals the skin over any cuts or bruises. A warm room or a heated garage with a damp cloth draped over the crates works. After curing, store at 55 to 60°F — not in the refrigerator, which damages the flesh — where they can hold for months.