Sweet potatoes grow from slips — rooted shoots off a mature tuber — not from seed potatoes. Start slips about 6 weeks before planting, set them 12 inches apart in rows 36 inches apart once nights hold above 60°F, and harvest in 90 to 120 days. Good companions are bush beans, dill and thyme.
Sweet potatoes are not potatoes
Worth settling in one sentence, because almost every mistake with this crop comes from treating it like an ordinary potato: they are unrelated plants, in different families, grown in different ways. A potato is a nightshade grown from seed potatoes planted before the last frost. A sweet potato is in the bindweed family, grown from slips planted well after it, and it wants heat where a potato wants cool.
One other distinction worth knowing: much of what is written about "sweet potato vine" concerns the ornamental varieties grown for their purple or lime foliage. Those are the same species bred for leaves rather than roots, and they do produce edible tubers, but they are selected for appearance and crop poorly. This page is about the edible crop.
Sweet potato companion plants
Good neighbours, and why.
Bush beans fix nitrogen and are short enough not to shade a sprawling vine. The pairing works mostly because the timing and height suit each other. Dill and other umbellifers flower and draw parasitic wasps and hoverflies, which is a genuine mechanism against the caterpillars that chew sweet potato foliage. Thyme and other low aromatics occupy the bed edge without competing for the root zone.
Bad neighbours, and why.
Squash and pumpkins are the main clash, and it is a straightforward one: both crops sprawl aggressively over the ground, and two sprawling crops in the same bed smother each other. This is a space conflict, not a chemical one. Avoid following a sweet potato with another root crop in the same ground — rotate to something above ground, because the soil-borne problems that affect roots build up when the same crop type returns.
Growing slips
This is the part that has no equivalent in ordinary potato growing.
Start about six weeks before your planting date. Take a firm, unblemished sweet potato — organic if possible, since some supermarket tubers are treated to suppress sprouting.
Two methods work. Suspend the tuber half-submerged in a jar of water, held up by toothpicks through its middle, on a warm windowsill. Or bury it lengthways in damp compost in a warm place, leaving the top just showing. Either way it wants warmth: around 75–85°F is where slips form quickly, and a cold sill stalls the whole process.
Shoots appear in two to four weeks, and one tuber produces a dozen or more. When a shoot reaches about six inches, twist it off at the base — do not cut the tuber — and stand it in a glass of water. Roots form within a few days. The tuber carries on producing more shoots for weeks, so a single sweet potato supplies a whole bed.
Plant out once the slip has an inch or two of root, burying it deep enough that only the top leaves show.
When to plant
Well after the last frost — wait for warmth, not the calendar. Sweet potatoes are a tropical crop and a cold check sets them back permanently rather than temporarily. Night temperatures should be reliably above about 60°F and the soil genuinely warm before slips go out, which is typically two to four weeks after the last frost date.
The planting date calculator gives the frost-relative dates; the soil temperature is the condition to check alongside it.
They need a long season — 90 to 120 days — so a late planting into cold soil rarely catches up. Black plastic laid over the bed a fortnight before planting warms the soil and is worth the trouble where summers are short.
How far apart to plant sweet potatoes
12 inches between plants, 36 inches between rows.
The vines will sprawl far beyond that and root wherever a node touches damp soil. That is normal and does not need stopping — the main crop still forms at the original crown.
Spacing controls size rather than yield: closer together gives more but smaller roots, wider apart gives fewer and larger ones. Twelve inches is the compromise most people want.
Growing in containers
They will grow in a container, and it needs to be a big one. Allow at least 5 gallons and 12 inches of depth per plant, and more is better — a half barrel or a large grow bag suits them. Depth matters here in a way it does not for a leafy crop, because the storage roots need somewhere to form.
Expect a smaller harvest than open ground, and let the vines trail over the sides rather than trying to contain them.
Soil, water and feeding
Loose, free-draining soil, because the crop has to swell through it. Heavy clay gives small, misshapen roots; a raised bed is a real advantage.
Water about an inch a week while the vines are growing, then ease off in the last few weeks before harvest. Heavy watering late causes the roots to split.
Go easy on nitrogen. This is the single most common growing error with sweet potatoes: rich soil and generous feeding give luxuriant vines and almost no crop. Phosphorus and potassium matter more. If a bed has just had a heavy nitrogen feed, plant something else in it — how to add nitrogen to soil covers which materials release fast enough to matter here.
Harvest and curing
Lift before the first frost, and certainly before frost blackens the vines — cold damage travels down into the roots and they will not store.
Dig carefully and wide of the crown. Sweet potato skin is thin and tears easily at harvest, and damaged roots rot in storage.
Then cure them, which is not optional if you want them to keep or taste sweet. Hold them at around 80–85°F in high humidity for about a week. Curing heals harvest wounds and converts starch to sugar, which is what turns a bland root into a sweet one. After curing, store somewhere cool but not cold — a refrigerator damages them.
Common problems
All leaves, no roots. Excess nitrogen. Covered above; the fix is the next bed rather than this one.
Small or stringy roots. Usually a short season, cold soil at planting, or heavy ground. Warm the soil before planting and give them the full 90 to 120 days.
Holes and chewing on the leaves. Usually caterpillars or flea beetles. Sweet potato foliage takes a lot of damage without the crop suffering, so tolerate more than you would on a leaf crop.
Roots that rot in storage. Almost always skipped or insufficient curing, or harvest damage.
Sweet potatoes make a good rotation partner for bush beans, which leave nitrogen behind for a following leaf crop rather than for this one.