How to Grow Potatoes

How a potato plant works

The part you eat is a tuber, a swollen underground stem, not a root. New tubers grow at the tips of underground stems (stolons) that sprout from the main stem above the seed piece. That one fact explains most of the routine. You plant fairly shallow, then pile soil or mulch up around the stems as they grow so there is covered stem for tubers to form on. If a tuber pushes into daylight, it turns green.

Potatoes are a cool-season crop. They grow best when days are mild and nights are cool. Tuber set and filling slow sharply once the soil gets above about 90°F, so the whole season is a race to get tubers sized before summer heat arrives. Clemson Extension points out that plants keep growing longer, and yield more, when the soil stays cool. That is one of the main reasons to mulch.

Frost tolerance is in between. Clemson says plants can handle a light frost but hard freezes set them back. Texas A&M says the tops can’t take frost at all, and NC State says they can tolerate a little. Texas A&M adds that a plant killed back by a late frost won’t regrow if its seed piece has rotted, and seed pieces rot fastest in cold, wet soil.

Start with certified seed potatoes

Buy certified seed tubers from a garden center or seed catalog. Grocery-store potatoes are often treated with sprout inhibitors, and the extension services in Georgia, Maine and New Hampshire all advise against planting them. Saving your own tubers is also a gamble. Utah State and Clemson warn that viruses build up from year to year, and Texas A&M says not to hold seed for more than a year. Utah State’s one exception is an heirloom variety you can’t buy anywhere else.

How much to buy: Utah State figures 8 to 10 pounds per 100 feet of row, and Clemson 12 pounds.

Cutting seed pieces

Small tubers can go in whole. University of Maine Extension suggests planting tubers under 2 inches across whole and not using anything smaller than 1 inch. Cut larger ones into blocky pieces about the size of a medium egg. Texas A&M aims for 1½ to 2 ounces, and Maine for 1¾ to 2¼ ounces. Pieces that are too small make weak plants because the seed piece feeds the sprout until its roots take over.

Each piece needs at least one good eye (Clemson, Texas A&M, Maine), and NC State and UGA prefer two. Make as few cuts as possible and keep the cut faces smooth. Maine notes that torn surfaces invite rot.

Sources differ on how long to let cut pieces heal before planting:

• Clemson: 3 to 5 days
• Texas A&M: 5 or 6 days in a well-ventilated spot
• NC State and UGA: about a day
• Maine: fresh-cut pieces can go straight in, or hold them at 50 to 55°F and over 90 percent humidity to heal

Healing matters most when the soil is cold and wet, or very hot. Those are the conditions where cut pieces rot.

Green sprouting for an earlier crop

In short-season areas, Maine recommends “green sprouting” (also called chitting) to gain a little time. Spread seed potatoes in a single layer in a bright spot at about 70°F with high humidity, and turn them now and then. They grow short, sturdy sprouts under an inch long. These come up quickly after planting and set tubers early.

Choosing varieties for your region

Variety advice is regional, so follow the recommendations closest to you.

• Southeast and Gulf states: Thick-skinned russets do poorly in the South, according to UGA, and NC State says they suit the western US better than the East. In North Carolina, NC State’s dependable choices are ‘Yukon Gold’, ‘Kennebec’ and ‘Red Pontiac’. Clemson notes that ‘Kennebec’ has done well in South Carolina’s Piedmont. UGA lists ‘Red LaSoda’ as tolerant of higher temperatures. UF/IFAS suggests ‘Red Pontiac’, ‘Yukon Gold’ and ‘Gold Rush’ for Florida.
• Texas: Texas A&M recommends reds such as ‘Red LaSoda’, ‘Norland’, ‘Dark Red Norland’ and ‘Viking’, whites such as ‘Kennebec’, ‘Superior’ and ‘Atlantic’, and ‘Yukon Gold’. Reds generally store longer, and whites generally cook better. That’s why Texas A&M suggests planting some of each and eating the whites first.
• Intermountain West: Utah State’s list includes the russets ‘Butte’, ‘Gem Russet’, ‘Ranger Russet’ and ‘Russet Burbank’, plus ‘Yukon Gold’, ‘Kennebec’, ‘Red Norland’, ‘Red Pontiac’ and ‘All Blue’.
• Northeast: Maine’s list includes ‘Superior’, ‘Red Norland’, ‘Kennebec’, ‘Yukon Gold’ and ‘Russet Burbank’. Maine also points to ‘Russet Burbank’ for scab resistance in higher-pH soil and ‘Kennebec’ for some late blight resistance.

Soil, pH and fertilizer

Potatoes need loose, well-drained soil. Poorly drained ground gives patchy stands, misshapen tubers and rot, and heavy clay tends to produce small, rough potatoes. Texas A&M builds beds 10 to 12 inches high, 36 inches apart, because drainage is so important on heavy Texas soils. UGA recommends raised beds for the same reason.

All the sources want slightly acidic soil, but their pH targets differ:

• Clemson: 5.8 to 6.5
• Maine: 5.3 to 6.0 is typical in potato production
• UGA: 4.8 to 5.4

The low end matters because of common scab, a soil-borne disease that leaves rough, corky patches on the skin and is worse in alkaline soil. Clemson notes that keeping pH between 5.0 and 5.3 sharply reduces scab in susceptible varieties. Lime only if a soil test calls for it, since Maine notes that higher pH favors scab.

Manure is another disagreement. Maine says not to use it on potatoes because it encourages scab. UGA recommends working in manure or compost in early spring. If scab has been a problem in your garden, follow Maine and use compost instead.

Feed early and moderately. Texas A&M and Maine both band fertilizer about 2 inches to the side of the seed piece and 1 inch below it, never touching it, because direct contact rots the piece. Too much nitrogen gives you big, leafy plants and delays tubers. Maine adds that overfed plants make tubers that store poorly. A single side-dressing is plenty, though the timing varies by source. Texas A&M side-dresses when plants are about 4 inches tall, and Utah State about 6 weeks after emergence. UF/IFAS notes that potatoes, like other tuber and root crops, respond to potassium.

Planting

Plant when the soil 4 inches deep reaches about 50°F. In most places that is 2 to 3 weeks before the average last frost. Check the dates for your zone above. Planting earlier doesn’t buy much. Maine notes that seed sitting in cold, wet soil is prone to decay, and Texas A&M warns that early plantings can have their tops frozen off. Utah State suggests planting through black plastic for an earlier crop because the plastic warms the soil.

Depth recommendations vary with climate:

• Texas A&M: cover seed about 3 inches deep; deeper planting slows emergence and invites disease and seed decay.
• Clemson: 3 to 5 inches, cut side down, and 5 to 6 inches for later plantings when the soil is warmer.
• Utah State: 4 to 6 inches.
• Maine: open a 4- to 6-inch furrow but cover the seed with only 2 inches of soil at first, then fill in by hilling.

Shallow planting in cold spring soil, followed by hilling, gets plants up fast and still gives the tubers plenty of cover.

Hilling and mulching

Because tubers form above the seed piece, the stems need more cover as the season goes on. Hilling also smothers small weeds and helps drainage. Start when the shoots are about 6 inches tall (Maine, UGA). Utah State says to hill within 4 weeks of planting. Maine says it can take up to three hillings to build a full hill. Keep the hoe shallow, because roots and stolons run close to the surface.

Mulch can do the same job. Texas A&M recommends a thick layer once plants are 8 to 10 inches tall to block light, cool the soil and improve yield. It also notes that tubers formed in soft mulch are often smoother than those grown in heavy soil. For a no-dig method, Clemson sets seed on the surface or an inch deep and covers it with 12 to 18 inches of straw or pine needles. Utah State plants 1 to 2 inches deep under 4 to 6 inches of mulch and adds more as it settles. Either way, many tubers form in the mulch and are easy to harvest.

Watering

Aim for 1 to 2 inches of water a week, soaking the top foot of soil where most roots feed (Utah State). Drip irrigation works well. UGA says heavier soils need watering about every 5 to 7 days and sandy soils more often. Clemson and UGA both say water is most critical when the plants are forming blossoms.

Consistency matters as much as amount. A dry spell followed by heavy watering or rain causes growth cracks and knobby “second growth.” Clemson ties alternating wet and dry soil to hollow heart, a cavity in the center of large tubers. Texas A&M adds that a hot, rainy spell after drought can make tubers sprout in the ground.

When the vines start to yellow, cut back on water. Late-season wet soil leads to rot in storage, and Texas A&M notes that too much water enlarges the pores on the skin, which also makes tubers rot more easily.

Regional differences

Cold north (northern tier, New England, upper Midwest): Your season is long enough, but spring soils stay cold and wet. Plant into the lightest, best-drained bed you have, because Maine notes that lighter soils warm and dry earlier. Green sprouting and black plastic both help you start sooner. Maine calls late blight the serious disease threat and advises home gardeners to protect plants with a labeled fungicide, partly because an infected garden can spread spores to commercial fields miles away. Late varieties are the ones to store over winter.

Humid Southeast: Spring is the season. Clemson doesn’t recommend fall potatoes in South Carolina because pests and diseases are heavier then. Choose thin-skinned reds, whites and yellows rather than russets. Plant on raised beds and mulch to keep the soil cool once spring turns hot. UGA lists heat necrosis (black streaks in the tubers) and heat sprouts among the problems hot weather causes.

Texas and the southern Plains: Texas A&M supports both a spring crop and a fall crop. The fall crop is planted about 110 days before the first expected frost. Plant small whole potatoes about 1½ inches across in fall, because cut pieces rot in hot soil. To break the tubers’ dormancy before planting, keep them warm and damp in the shade under moist burlap or mulch for 2 weeks so they have small sprouts at planting. Many gardeners buy extra seed in spring and hold it in the bottom of the refrigerator for fall.

Arid West and high desert: Utah State’s frequently asked question about small, odd-shaped tubers comes back to soil temperatures above 90°F. Mulch heavily and water deeply and evenly to keep the root zone cool. In the low desert around Phoenix, University of Arizona’s planting calendar treats potatoes as a winter-planted crop and shows no fall planting.

Warm-winter areas (Florida, the Gulf Coast, low desert, zones 9-11): Potatoes are grown from fall into winter and dug before summer heat. UF/IFAS stresses cool temperatures, steady moisture and generous fertilizer. Check the dates for your zone above, as the window shifts from North to South Florida.

Rotation

Texas A&M calls a good rotation an effective way to control most potato diseases. It advises planting potatoes in the same spot no more than once every 3 years. It also says not to plant them right before or after tomatoes, peppers, eggplant or okra. After a spring crop, Texas A&M suggests following with southern peas. Lists of good potato “companions” are garden tradition, not tested advice.

Common problems and fixes

• Colorado potato beetle: Yellow-and-black striped adults and reddish, black-spotted larvae strip the leaves. Handpick adults and crush the yellow egg clusters on leaf undersides. Utah State notes the beetles resist many insecticides, so use sprays sparingly.
• Flea beetles, aphids, leafhoppers: Flea beetles chew small round holes in young leaves. Aphids spread viruses, which is one more reason to start with certified seed.
• Wireworms and white grubs: These bore into seed pieces and tubers (UGA).
• Early blight: Target-like brown spots start on the oldest leaves. Avoid evening irrigation and keep fertility up. Use a fungicide only after the disease is confirmed (Utah State).
• Late blight: Water-soaked spots spread fast in cool, wet weather, sometimes with white mold at the edges. Use certified seed, water early in the day, and protect plants as Maine advises. NC State notes it can rot the tubers.
• Common scab: Corky patches on the skin. Keep pH low, skip fresh manure, and choose resistant varieties.
• Green tubers: Light exposure. Keep them hilled and store them in the dark.
• Knobs, cracks, hollow heart: Uneven moisture. Mulch and water on a schedule.
• Wilting from the bottom up: Utah State points to Fusarium and Verticillium wilts. Get a diagnosis, rotate, and use resistant varieties where they exist.
• Black walnut wilt: Clemson lists this for plants growing too close to a black walnut tree.

Harvest and yield

New potatoes can be dug about 7 to 8 weeks after planting, around the time the plants flower. Storage potatoes are ready once the vines have died back and the skins have set. That usually takes 85 to 120 days, depending on the source and on whether the variety is early, mid or late. Expect 75 to 100 pounds per 100 feet of row (Utah State), or 1 to 2 pounds per foot (Maine). Utah State suggests 50 feet of row per person for fresh eating and another 50 for storage. For digging, curing and storage details, see when to harvest potatoes.