Vegetable · Convolvulaceae
Sweet Potato
Ipomoea batatas
Give it warm soil and full sun and the sweet potato lays down a low mat of leaves over fat, swelling roots.
Full sun
Every 5–7 days
64–95°F · 18–35°C
90–120 days
Overview
Up close, the sweet potato reads as a low carpet of leafy stems with fat storage roots buried beneath. It is a heat-loving vine of the morning glory family, unlike the Irish potato of the nightshades, which shares only the name. Left a long, warm season, its running stems knit into a dense green sheet across the bed while the roots thicken below.
The stems trail a long way, 3 to 15 feet (90 cm to 4.5 m), lying flat and covering the soil so completely that weeds struggle through. At the growing ends the shoot tips stay soft and tender, the same young leaves and tips that cook down like spinach across much of the world. Below the surface, the true crop swells fat and heavy, hidden from view.
The plant hugs the ground and never stands tall, and every part of it leans on heat. In cold soil the stems sit still, and a frost kills them outright, so the roots only bulk into their full, heavy size given a warm bed and a long, hot summer.
Care
The short version: give the sweet potato full sun and loose, well-drained soil ridged up around it, about 1 inch of water a week eased off near harvest, and a light low-nitrogen feed so it fills out roots instead of piling on leaf.
Light
The sweet potato wants full sun, six to eight hours of it, to build the sheet of leaves that feeds the swelling roots. It takes a little afternoon shade, but under fuller light the canopy runs thicker and the roots below grow heavier.
Water
Give it about 1 inch of water a week in deep soakings, letting the surface crust dry between them. Taper off near harvest, since a sudden drink after dry ground swells the roots so fast their skin splits and cracks.
Soil
Set it in loose, well-drained loamy or sandy soil, mounded into raised ridges that give the fattening roots room to lengthen without sitting wet. The plant leans slightly acidic, a pH of 5.5 to 6.5.
Temperature
This is a tropical plant that soaks up heat, thriving from 64°F to 95°F (18°C to 35°C). Cold soil stalls the stems, and frost kills them outright, so it waits out a cold spring.
Humidity
Everyday summer air in the 40% to 70% range suits it, and outdoors the figure hardly registers on the plant. Heat and light shape this crop far more than the moisture around its leaves.
Feeding
Feed it sparingly. A low-nitrogen fertilizer such as 5-10-10 worked in before planting, then a single sidedress before the vines close over the row, is plenty. Too much nitrogen throws up a thick mass of leaves and leaves the roots thin and underfed.
Pruning
The roots need no pruning. Cut the trailing vines back only to tidy a bed or check their spread, and the soft shoot tips you remove cook down as tender greens.
Size & spacing
The leafy top stays low, just 6 to 12 inches (15 to 30 cm) off the ground, while the stems creep out 3 to 15 feet (90 cm to 4.5 m) in every direction. Give each plant open ground to run across, or fold the vines back so they do not bury their neighbors.
When to plant
The sweet potato lives and dies by warmth, with no room for frost. The sprouts, or slips, rise from a stored root indoors in late winter, the tender young plants go out only once spring has warmed the soil, and the swollen roots are lifted in fall before frost reaches them.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Sprout slips from a stored root indoors 6-8 weeks before transplanting
- Plant: After all danger of frost once soil is warm, roughly April through early July
- Harvest: Harvest storage roots in fall before the first frost
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
Nearly every sweet potato problem hides below the soil and turns up only when a root is lifted and its skin and flesh come into view. A short cast of pests and a single fungus mark the crop, and reading those signs on the root lets you dig clean ones season after season. Match the look of the damage below, then act before next season.
Stem-end pinholes over dark, frass-packed tunnels
The sweetpotato weevil does the worst damage of any pest here, and its marks are easy to read. Near the stem end the skin shows tiny chewed holes, and a cut reveals tunnels packed with frass and flesh gone dark and bitter. Lift every marked root and vine, destroy them, and keep none back for next year's slips.
Fix:
- Remove and destroy infested roots and vines
- Do not save infested material for propagation
Ragged holes gouged through the root flesh
Wireworms, the slim, hard-bodied larvae of click beetles, chew shallow pits that widen into deep, ragged holes as the root fills out. Their tunnels show as rough, round openings in the skin, with the wiry larvae still working the surrounding soil. Ground lately under grass breeds them, so lift the roots as soon as they size up.
Fix:
- Harvest promptly once mature to limit feeding time
- Avoid planting in recently turned sod
Dark brown to black patches across the root skin
Scurf shows as dark brown to black blotches that spread over the skin and run together, but the stain is only skin deep. Cut through and the flesh beneath is still firm, sound, and good to eat. The fungus arrives on infected stock, so set aside the worst roots and start the next crop from clean, disease-free slips.
Fix:
- Discard heavily affected roots
- Start next crop only from clean, disease-free slips
Toxicity
There is nothing on this plant to fear, in leaf, stem, or root: the sweet potato is safe for people and pets. The ASPCA lists the vine as non-toxic to cats, dogs, and horses, and the cooked root and tender green shoots feed people and animals alike. No part of it needs to be kept out of reach.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Safe around a cat. A mouthful of the trailing vine will not poison it, though a big helping of any leafy greenery can bring on a little drool or a short bout of upset stomach.
Dogs None
No toxic principles sit in leaf, stem, or root, and cooked sweet potato already fills out many dog foods. Keep portions modest, since a gut packed with fibrous root or vine can loosen the stool.
Horses None
A horse can crop the foliage with no poisoning risk. As with any rich new feed, bring it in slowly so the digestion has time to catch up.
Rabbits Safe
The leaves and soft vine tips make safe forage, and a little cooked root is fine as well. Go easy, because too much of the starchy root at once can upset a rabbit's sensitive gut.
Livestock Safe
Cattle, goats, and sheep browse the leafy vines and the swollen roots with no harm, and in many places the foliage is grown as fodder. Steady clean water and a gradual change of feed keep things settled.
Birds Safe
Chickens and other poultry peck cooked root and chopped greens with no danger. Offer it as one part of a varied diet rather than the whole meal.
People Safe
For people, the cooked root is a nourishing staple, and the young leaves and soft shoots are eaten as a cooked green. Eat it freely, keeping in mind only that the raw root is hard to digest in quantity.
Although non-toxic, eating large amounts of any plant material can cause mild stomach upset in pets.
Varieties
Hundreds of cultivars exist, but a few orange-fleshed kinds fill most gardens, and their color shows the moment a root is cut. These few are worth knowing by sight.
Beauregard
A widely grown kind whose orange flesh comes with heavy yields and a maturity earlier than most.
Covington
An NC State selection wrapped in rose-colored skin over orange flesh, cutting into even, dependably sweet roots.
Georgia Jet
A fast orange-fleshed type that fills out in shorter, cooler seasons where slower kinds run out of time.
How to propagate
The sweet potato never starts from seed in the garden. It grows from slips, the leafy sprouts that a single stored root pushes out, so one fat tuber becomes a whole bed of rooted young plants.
Stem cuttingsEasy
Spring, after the soil has warmed and frost danger has passed · 2 to 3 weeks
New plants come from slips, the rooted, leafy sprouts that break from a stored root once it starts to shoot. Set out as cuttings after spring soil warms and frost has passed, they catch and put down roots within 2 to 3 weeks.
Myths
Every part of the sweet potato plant is poisonous because it belongs with the toxic morning glories.
In truth the roots and cooked leaves of the food sweet potato are eaten the world over, and the ASPCA lists the plant as non-toxic. The real culprit is the seeds of certain ornamental morning glories, which are separate Ipomoea species and no relation to the food on the plate.
Sweet potatoes and ordinary Irish potatoes are the same kind of plant.
The two barely share a branch. The sweet potato is a trailing vine of the morning glory family whose roots fatten into storage organs, while the Irish potato belongs among the nightshades and forms its tubers on underground stems.