Vegetable · Solanaceae
Potato
Solanum tuberosum
Beneath leafy green stems, starch-swollen tubers fatten in the dark, their skins studded with eyes.
Full sun
Every 3–7 days
50–77°F · 10–25°C
70–120 days
Overview
The potato is a cool-season member of the nightshade family, kin to the tomato and pepper, and it carries the family's leafy, sprawling green growth above ground. It was bred for food in the Andes over thousands of years before it spread worldwide. The part that matters sits underground: the tuber, a swollen stem thick with starch, firm and rounded rather than rooted and threadlike, so it is no root at all.
The plant's life story is written underground, out of sight. A cut piece of seed potato, each one dimpled with an eye, sends up leafy green stems while short shoots below swell and round out into tubers. The one shaping act is hilling, banking soil up the pale lower stems so the tubers stay buried in the dark. A tuber that meets the light greens at the skin and just beneath it, and that green tissue tastes bitter.
Underground, the tubers thicken into firm, starchy lumps whose skins range from thin yellow to rough red-brown depending on the variety. Even a small planting fills out into a heavy handful of them by season's end, and their sturdy skins store well through the cold months. The plant gives back far more mass below the soil than its modest leafy top suggests.
Care
The short version: the potato wants full sun on its leafy tops, loose slightly acidic soil rich in organic matter, and even moisture once the tubers begin to round out underground. Feed at planting, keep the nitrogen low so the plant fills tubers rather than leaves, and mound soil up the stems as they grow.
Light
The potato's leafy green tops run on full sun, ideally 6 or more hours of direct light a day, which they turn into the starch that fills the tubers. In partial sun the stems come up thinner and weaker and the tubers stay small, so the most open, sunlit ground suits them best.
Water
The soil under a potato should stay evenly moist, roughly 1 to 2 inches of water a week, most of all once the tubers begin to round out and swell. Waterlogged ground, dark and sodden, brings on rot and disease at the tuber, so steady dampness beats a soaked bed.
Soil
Potatoes sink their tubers into loose, well-drained sandy loam dark with organic matter. They favor acidic ground, a pH of 5.0 to 6.0, which also holds back the corky patches of scab. The crumbly, open texture lets each tuber press outward and swell into a full, rounded shape.
Temperature
The potato swells its tubers best in cool air, between 50°F and 77°F (10°C to 25°C). As the heat rises the underground growth slows and the tubers stall, so an early start lets them bulk up before the warm months. The leafy top will keep standing through a hot spell, but the real work below pauses.
Humidity
Ordinary outdoor humidity is enough for the potato, so no set number applies. Airflow through the leafy canopy matters far more, since still, damp air trapped among crowded green foliage is where the wet lesions of late blight begin. Space between plants keeps the leaves drying.
Feeding
A balanced fertilizer worked into the dark soil at planting feeds the young plant, with a little nitrogen side-dressed as the green shoots break through and the hilling begins. Too much nitrogen swells the leafy tops into a thick green mass while starving the tubers below, so a restrained hand keeps the growth where it counts.
Pruning
The potato needs no real pruning to shape it. Diseased leaves, spotted and browning, are pulled off as they appear, and soil is hilled up the pale stems to bury the swelling tubers and keep the light from greening their skins. That mounding is the one hands-on act that shapes the crop.
Size & spacing
The leafy plant stands 1 to 3 feet (30 to 100 cm) tall and spreads 12 to 24 inches (30 to 60 cm) wide, a low green mound above ground. Give it room and pile the soil up around the stems, since the dark, buried space beneath is where the rounded tubers form and fill out.
When to plant
The potato starts into growth early, while the soil is still cold to the touch. The cut seed pieces go in 2 to 4 weeks before the last frost, once the ground reaches around 45°F to 50°F (7°C to 10°C), and pale sprouts soon push up through the surface. Small new potatoes can be dug by midsummer, thin-skinned and tender, while the main crop firms up underground and is lifted in fall once the leafy tops have yellowed and died back.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Early spring, about 2-4 weeks before the last expected frost once soil reaches roughly 45-50°F
- Harvest: Harvest new potatoes about 60-70 days after planting; harvest mature storage potatoes about 90-120 days after planting once tops die back
Hardiness
USDA hardiness zones: 3–9
Temperature: down to -40°C
Troubleshooting
Most potato troubles announce themselves visibly, either as marks on the green foliage while the plant grows or as blemishes on the tubers once they are dug. A few are worth knowing on sight so you can act early. Match the look of what you see below, then deal with it while it still counts.
Wet-looking dark blotches and slumping, blackened foliage
These water-soaked dark blotches are late blight, the Phytophthora that also strikes tomatoes, and it blackens a planting fast after a cool, damp spell. On humid mornings the lesions spread brown to black with pale, bleached margins, and a fine white fuzz coats the leaf undersides. Pull and destroy the collapsing plants at once rather than composting them, and cut out any tuber gone to reddish-brown granular rot before it reaches storage.
Fix:
- Remove and destroy infected plants immediately
- Do not compost infected material
- Apply an approved fungicide preventively where blight is present
- Harvest carefully and cull infected tubers before storage
Yellow-striped beetles and soft red grubs chewing ragged leaves
The Colorado potato beetle is the crop's worst pest, its adults rounded and yellow with ten black stripes down the back, and a heavy brood can chew the leaves to bare ribs. Look under the foliage for clustered orange eggs and the soft, humpbacked red larvae feeding beside them. Handpick every stage into soapy water, drape row cover over young plants, and move the planting to fresh ground each year.
Fix:
- Handpick adults, larvae, and egg masses into soapy water
- Use row covers early in the season
- Apply an approved insecticide if infestation is heavy
- Rotate planting location yearly
Green staining spreading across the tuber skins
The green stain that creeps over a tuber's skin, and the layer just beneath it, is chlorophyll paired with solanine, the toxin that leaves the flesh bitter and unsafe. It shows up wherever light has reached a tuber left too shallow by thin hilling. Bank soil over the exposed tubers as the plants grow, throw out any stained deep green, and store the crop somewhere cool and dark.
Fix:
- Hill soil up over exposed tubers as plants grow
- Discard heavily greened tubers
- Store harvested potatoes in cool, dark conditions
- Cut away minor green areas before cooking
Rough, corky brown patches crusting the tuber skins
These rough, corky brown patches are common scab, a soil bacterium that raises them when the ground goes dry during tuber set or the pH climbs too high. Pare one open with a knife and the damage proves shallow, a crust over sound, firm flesh, so the potato still eats well. Keep the soil evenly moist as the tubers form, hold the pH down around 5.0 to 5.5, and leave the fresh manure out of the bed.
Fix:
- Maintain even soil moisture during tuber formation
- Keep soil pH slightly acidic (around 5.0-5.5)
- Plant scab-resistant cultivars
- Avoid fresh manure and alkaline amendments
Toxicity
There is a sharp split in this plant between what is safe and what is not. The cooked tuber is a safe, everyday food, but the leafy green tops, the stems, the sprouts, and any tuber gone green or eaten raw carry a natural toxin called solanine. That solanine sits in the green tissue and turns a potato bitter, and it can sicken people and animals, so cut away green skin, discard badly greened tubers, and keep the vines and sprouts out of reach of pets, livestock, and children.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
A cat that bites into the green leaves, the stems, or a green sprouted tuber swallows solanine, and the first signs are heavy drooling and vomiting, with diarrhea and a limp, low mood soon after. A large mouthful can reach the heart and nervous system, so anything past a nibble is worth a call to the vet.
Dogs Caution
A dog that unearths and gnaws a raw or green tuber, or strips a few leaves, usually ends up with a churning stomach, loose stools, and a dull, dragging mood. Keep a close eye, since a bigger dose of the glycoalkaloid can unsettle the heart's rhythm.
Horses Caution
The leafy vines and any green or sprouted tubers are off limits to a horse. Solanine brings on colic, ropey drool, and a dull, swaying stance, and a horse cropping fallen foliage can take in enough to need the vet.
Rabbits Caution
The leaves, stems, and green tubers are real danger to a rabbit, whose small body feels even a little solanine sharply. A rabbit that eats any tends toward a lost appetite, a swollen, bloated belly, and visible weakness.
Livestock Caution
Cattle, sheep, pigs, and goats poison themselves on tossed-out vines or heaps of green and cull tubers left in the field. The solanine churns the gut first, then adds a staggering, trembling unsteadiness once enough has gone down.
Birds Caution
Chickens and other birds should stay clear of the green foliage, the sprouts, and any greened scraps, all of which hold solanine. A little plain cooked potato does no harm, but the raw, green pieces do.
People Cooked tuber safe
A cooked, pale-fleshed potato, stored well, is a safe everyday staple. The danger lives in the green skin, the sprouts and the eyes, and the whole leafy top, all carrying solanine that turns a potato bitter and can make you ill, so pare away green patches, throw out any tuber stained deep green, and keep the vines off the plate.
Cooked, properly stored potato tubers are a safe food. The hazard is the foliage and any green, raw, or sprouted tubers, which contain solanine.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Hundreds of potato varieties exist, told apart most readily by the color of their skin, the texture of the flesh inside, and how they cook. The four below show off that range, from thin yellow skins to rough brown ones.
Yukon Gold
Yukon Gold wears a thin yellow skin over buttery, all-purpose yellow flesh, the look that has made it the standard kitchen potato.
Russet Burbank
Russet Burbank is large and oblong under a rough brown skin, its dense starchy flesh the reason it dominates the baking tray and the fryer.
Red Pontiac
Red Pontiac shows a smooth red skin around clean white flesh, and it pairs steady yields with tubers that keep firm in storage.
Kennebec
Kennebec is a big, pale white potato with a vigorous top, cropping heavily and shrugging off more disease than most.
Companions
Potatoes do well beside nitrogen-fixing beans and a few traditional partners, and badly beside their nightshade relatives and sprawling vines that crowd them and trade diseases.
Plant near
Bush beans: Legumes fix nitrogen and are reported to help repel some potato pests.
Corn: Traditional companion that does not compete heavily and shares no major potato diseases.
Cabbage-family crops: Generally compatible bed companions that do not share potato's key diseases.
Horseradish: Often planted near potatoes and is said to improve overall plant vigor and pest resistance.
Keep apart
Tomato: Another solanaceous crop that shares late blight and other diseases, increasing risk to both.
Cucumbers and squash: Sprawling cucurbits crowd potatoes and can increase disease pressure.
How to propagate
There are two ways to raise a potato, but one produces the familiar tuber crop while the other rarely does, so nearly every grower takes the first.
Bulbs & cormsEasy
Early spring, 2-4 weeks before the last frost · Sprouts emerge in about 2-4 weeks after planting
Almost every crop starts from cut pieces of certified seed potato, each chunk carrying one or two eyes and left a day or two until the cut face dries to a dull skin. The pieces go into the ground in early spring, 2 to 4 weeks before the last frost, about 4 inches deep, and pale sprouts break the surface in roughly 2 to 4 weeks. Soil is then banked up the stems as the leafy plant climbs.
SeedDemanding
Indoors in late winter · Several weeks to germinate and grow on before transplanting
Growing from true botanical seed is a slower, finer business, the tiny seed started indoors in late winter and nursed along for several weeks before the seedlings are strong enough to transplant. The plants come up mismatched and unpredictable, so home growers rarely try it and the method stays with breeders.
Myths
Every part of the potato plant can be eaten, since the tuber itself is.
Only the cooked tuber, stored well and still pale inside, is safe on the plate. The green leaves, the stems, the sprouts, and any tuber gone green or eaten raw hold solanine, a genuine toxin, so the plant as a whole is not food. The pale, starchy tuber is the single edible part, and even it turns dangerous once it greens.
Potatoes must be grown from true seed, as most vegetables are.
Almost every grower plants cut pieces of seed potato instead, each chunk carrying an eye that sprouts into a new plant. True botanical seed is seldom used beyond breeding, since it yields a scattered, unpredictable mix of seedlings rather than the tuber a grower expects. A handful of eyed seed pieces is all it takes.