The potato (Solanum tuberosum) is a nightshade, kin to tomatoes and peppers, grown from pieces of tuber rather than seed - and that decides most of how you grow it.
Potatoes are one of the most generous things you can grow: a few pieces of tuber in spring, a fork in the ground at the end of summer, and a pile of potatoes you grew yourself. Most of the skill is in a handful of decisions made before and around planting.
Solanum tuberosum - the potato, and a nightshade
Solanum tuberosum is the ordinary potato. It belongs to the nightshade family (Solanaceae) along with tomatoes, peppers, eggplant and tomatillos. That family tie matters more than it sounds, because those crops share diseases, which is why they share a rotation.
The part you eat isn't a root. A potato tuber is a swollen underground stem that forms at the tip of a runner growing out from the piece you planted. The plant does flower, and it sometimes sets small potato-like fruits with seed inside, but that seed won't grow true to the variety. Potatoes are grown from tubers, not seed.
Start from seed potatoes, not the grocery bag
Because the new plant grows straight from a piece of the old tuber, whatever the old tuber carried comes along with it. That's why the start matters:
PromisingPotatoes are grown from certified seed potatoes - disease-free seed tubers from a certified source - not from saved tubers or grocery-store potatoes. Large seed tubers are cut into blocky pieces, each with at least one eye, and the cut surfaces left to dry to a tough protective skin before planting. Grocery-store potatoes may be treated to stay dormant and can carry disease that persists in the soil.
ignored, it still works, just worse · the planner suggests it
Mechanism: Potato is propagated vegetatively - the crop grows from a piece of tuber, not from true seed - so any virus or disease in the seed tuber is passed straight to the new plants and can remain in the soil for years; certified seed is inspected, disease-free stock, which is why saving one's own tubers or planting grocery potatoes risks introducing disease. Each planted piece must carry an eye, the bud the new shoot grows from. A freshly cut piece exposes moist flesh that storage and soil rots colonise; holding the cut pieces a few days until the surface dries and forms a corky protective layer (suberises) seals that wound before planting. Grocery tubers may additionally be treated with a sprout inhibitor, so they are slow to grow.
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
UMN Extension, 'Growing potatoes in home gardens', extension.umn.edu/vegetables/growing-potatoes (read 2026-08-22): 'Buy disease-free seed tubers from a certified grower or seed distributor'; 'Every piece must have at least one "eye," an indentation that will produce the new shoot'; 'Place the cut pieces on a tray at room temperature (between 60 F and 70 F) for a few days until the cut surface has dried out and formed a tough protective layer'; 'Do not plant potatoes purchased at the grocery store, as the store may treat them with chemicals to keep tubers dormant, in which case they will be slow to grow. Diseases may also infect the potatoes, which can remain in the soil for a long time.'
Utah State Univ. Extension, 'How to Grow Potatoes in Your Garden', extension.usu.edu/yardandgarden/research/potatoes-in-the-garden (read 2026-08-22): 'When buying seed tubers, ask for certified seed as this will help reduce the potential for introducing disease into the garden'; 'When cutting, make sure the seed piece weighs at least 2 ounces and has one or more "eyes"'; 'saving your own seed potatoes leads to a buildup of viruses and diseases that eventually will cause serious problems in the garden. Whenever possible, purchase and plant certified seed to help control many of the problem diseases potatoes experience.'
remedy
Buy certified seed potatoes. Cut large ones into blocky pieces of about two ounces, each with at least one or two eyes; leave small tubers whole. Spread the cut pieces at room temperature (about 60-70 F) for a few days until the cut surface has dried and formed a tough skin, then plant. Do not plant grocery-store potatoes (possible sprout inhibitor, and disease that lingers in the soil) and do not replant your own saved tubers year to year (virus and disease build up).
Read the full rule → · open in the planner ↗
A large seed potato can be cut into blocky pieces of about 40–60 g1½–2 ounces, each with at least one good eye. Small seed potatoes can go in whole. Leave cut pieces somewhere at room temperature for a few days, until the cut face has dried to a tough skin, which helps the piece resist rot once it's planted.
For an earlier start, you can pre-sprout ("green sprout") whole seed potatoes. Keep them in the dark at room temperature until they sprout, then move them into the light so the sprouts stay short and sturdy. Cut and plant as usual.
When to plant, and how deep
Potatoes are half-hardy: they'll take a light frost, so they don't have to wait for the tomatoes' frost-safe date. The planner puts them on the early window:
PromisingCold-hardy annuals can be sown or transplanted before the last spring frost — hardy crops about three weeks before, half-hardy about two weeks before. Tender crops wait for the frost itself.
ignored, it still works, just worse · the planner suggests it
Mechanism: Cold hardiness. Hardy crops tolerate hard frost and half-hardy crops tolerate light frost, so they can occupy the ground weeks before frost-tender crops are allowed in. The offset is measured from the last spring frost.
Evidence: confirmed against 4 sources in the research-based literature.
the 4 sources
University of Illinois Extension, 'Time Your Vegetable Plantings by Cold Hardiness' (2018-03-26), extension.illinois.edu/blogs/ilriverhort/2018-03-26-time-your-vegetable-plantings-cold-hardiness: very hardy vegetables 'withstand freezing temperatures and hard frosts without injury' (planted earliest in spring); frost-tolerant vegetables 'can withstand light frosts, but not freezing temperatures' (planted a couple of weeks later). LLM-summarised from a read of the page; it establishes the CATEGORIES but states no week offsets.
Colorado State Univ. Extension, GardenNotes #720, 'Vegetable Planting Guide', extension.colostate.edu/resource/vegetable-planting-guide (read 2026-07-25): hardy vegetables go in 'As early as 2-4 weeks before the date of the average last spring frost'; semi-hardy 'As early as 0-2 weeks before the date of the average last spring frost'; tender from seed 'around the date of the average last spring frost'; very tender 'Typically 2+ weeks after'. This is the source that states the offsets in weeks.
Where this rule sits in that range: hardy at 3 weeks is mid-range of CSU's 2-4. Half-hardy at 2 weeks is the EARLIEST EDGE of CSU's 0-2 - the most aggressive planting CSU sanctions, not the middle of it. The rule is inside published guidance at both ends, but it leans early on the half-hardy side and a gardener following it in a cold spring is taking that boundary.
Do not import an offset from another publication's hardiness scheme without checking the category names: CSU has no 'very hardy' tier, so a '4-6 weeks before frost' figure written against a four-tier scheme does not describe CSU's 'hardy'. Categories are not comparable across sources.
Read the full rule → · open in the planner ↗
Soil temperature matters as much as the calendar. Plant once the soil has warmed to at least 7°C45°F. Seed pieces planted into a long, cold spell sit there and can rot, and hard frosts set the young plants back.
Plant the pieces cut side down, 8–13 cm3–5 inches deep and about 25–30 cm10–12 inches apart, in rows 75–90 cm30–36 inches apart. Closer spacing gives you more, smaller potatoes; wider spacing gives fewer, bigger ones.
Potatoes come in early and late types. Early ones give you tender new potatoes, and later ones give you the potatoes that keep for months. Growing one of each spreads the harvest out. The planner knows three types: first early (new potatoes), second early, and maincrop (for storage). Tell it which one you're growing and it narrows the harvest window to that type. The day counts for each type are estimates for now, so take them as a guide.
Hilling keeps the light off
New potatoes form close to the piece you planted, near the surface, and a tuber that catches light turns green. Hilling means drawing soil up around the stems to cover them:
PromisingPotato tubers that catch light while growing - wherever soil settles or washes away and shallow tubers are left uncovered - turn green and become bitter and toxic, so the crop must be kept covered with soil rather than left exposed at the surface.
ignored, it still works, just worse · the planner suggests it
Mechanism: Tuber tissue exposed to light produces chlorophyll and, in that same tissue, synthesises the toxic glycoalkaloids solanine and chaconine, so soil mounded over the developing tubers keeps light off them and prevents both the greening and the toxin from forming.
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
Penn State Extension, 'Potatoes in the Garden and the Kitchen', extension.psu.edu/potatoes-in-the-garden-and-the-kitchen (read 2026-08-21): 'Tubers exposed to sunlight (both before and after harvest) will turn green and should not be eaten'; 'Sun exposure causes the potato''s skin to produce chlorophyll and, along with it, two toxic compounds, solanine and chaconine. These cause the potato to have a bitter taste ...'; 'When the plant stems are 8 to 12 inches tall, gently hill or mound the soil around the base of the plant, covering most of the stem. You may repeat this mounding practice two or three times as the plants grow.'
UMN Extension, 'Growing potatoes in home gardens', extension.umn.edu/vegetables/growing-potatoes (read 2026-08-21): 'Green skin occurs when potato tubers experience exposure to light'; 'Hilling also keeps any shallow tubers from exposure to light and turning green.'
remedy
Hill the crop: once the stems are roughly 8-12 inches (20-30 cm) tall, draw loose soil up around the base of the plants to cover most of the stem and bury any shallow tubers, and repeat two or three times through the season so the tubers stay covered. Green tubers are bitter and should not be eaten; the green signals the toxin is present and is not reliably removed by peeling, so the defence is to keep light off the tubers in the first place - in the ground, and again in dark storage.
Read the full rule → · open in the planner ↗
Start hilling when the stems are about 30 cma foot tall, and hill once or twice more as they grow. By the end of the season you'll have added about 15–20 cm6–8 inches of soil along the row. Some gardeners plant in a shallow trench instead, then fill it back in as the plants grow. Once you've finished hilling, a thick straw mulch keeps the soil cool and moist.
If a potato does turn green, cut the green parts away before cooking. Don't eat potatoes that are green over much of their surface.
Water them steadily
Potatoes want even moisture, especially while the tubers are forming. If they run short early on, you can get knobby or hollow potatoes, and too much water causes its own problems. Soak the bed thoroughly once or twice a week, aiming for about 2.5 cman inch of water a week including rain. Sandy soil needs watering more often. Water at the base rather than over the leaves, because wet foliage spreads fungal disease. The watering guide covers the rest.
Digging new potatoes and keepers
New potatoes are ready about seven or eight weeks after planting, usually once the plants have flowered. Dig gently with a garden fork so you don't bruise or spear them.
For potatoes you want to keep, wait until the tops have died back, then leave the tubers in the ground about two more weeks so their skins toughen. Dig on a dry day, and don't dig when the soil is wet. Every cut or bruise is a way in for rot. Brush off loose soil, but don't wash them.
Before storing them, let the potatoes cure: give them ten days to two weeks somewhere dark and airy so the skins set and small nicks heal. Then store them cool, dark and unwashed. The harvest and keeping guide covers curing and storage in detail.
Scab, blight and next year's bed
Common scab leaves rough, corky patches on the skin. It's ugly, but a scabby potato is perfectly good to eat. Scab gets worse as soil becomes less acid, which is why the usual garden habit of liming works against potatoes:
PromisingLimed ground is the wrong ground for the next potato crop: common scab worsens as soil pH rises, and lime raises it.
ignored, it still works, just worse · the planner suggests it
Mechanism: Common scab (Streptomyces scabies) infects young tubers through the lenticels and is favoured as soil goes less acid; at about pH 5.2 and below it is largely suppressed. Lime raises pH and its effect lasts years, so ground limed for a crop that wants sweet soil carries a scab-prone pH into the seasons that follow.
Evidence: confirmed against 5 sources in the research-based literature.
the 5 sources
UMass Extension, 'Potato, Scab', umass.edu/agriculture-food-environment/vegetable/fact-sheets/potato-scab (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Common scab is controlled or greatly suppressed at soil pH levels of 5.2 or lower'; 'Avoid application of soil amendments that increase soil pH'; 'Increase rotation with nonhost crops to 3-4 years'; 'Maintain adequate soil moisture during and after tuber set.'
Wisconsin Horticulture Extension, 'Potato Scab', hort.extension.wisc.edu/articles/potato-scab (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Scab tends not to develop when the soil pH is less than 5.2'; 'For home gardens, keeping the soil pH at approximately 6.5 is a good compromise'; 'Avoid using fertilizers (e.g., lime, calcium and potassium nitrate, or fresh manure) that may increase soil pH'; the disease 'can also affect other root vegetables such as beets, carrots, parsnip, radish, rutabaga, salsify and turnip.'
Clemson HGIC, 'Irish Potato & Sweetpotato Diseases', hgic.clemson.edu/factsheet/irish-sweet-potato-diseases (fetched in-container 2026-09-02; read by the maintainer 2026-09-02), common scab: 'Soil pH should be between 5.0 and 5.2'; 'avoid alkaline materials, especially lime and wood ashes, but also avoid mushroom compost and leaf compost. All of these will raise the soil pH'; 'Scab is favored under low soil moisture conditions, so the garden soil must be kept moist during the active growing period of the tubers (particularly 4 to 9 weeks after planting)'; 'Do not plant Irish potatoes after beets, carrots, radishes, parsnips, rutabagas, or turnips, which are also susceptible to scab.'
Univ. of Maryland Extension, 'Common Scab of Vegetables', extension.umd.edu/resource/common-scab-vegetables, and 'Growing Potatoes in a Home Garden', extension.umd.edu/resource/growing-potatoes-home-garden (both fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'The disease is encouraged by soil pH above 5.5'; 'Where potato scab disease is a persistent problem, a soil pH of 4.8 to 5.8 is recommended'; 'It can also be a problem of beets, carrots, parsnips, turnips, and radish.'
Univ. of Maine Cooperative Extension, Bulletin 2077, 'Potato Facts: Growing Potatoes in the Home Garden', extension.umaine.edu/publications/2077e (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'a soil pH of 5.3 to 6.0 is typical for potato production'; 'higher soil pH levels are more conducive to scab, a potato disease caused by a soil-borne pathogen'; 'Lime will also raise the pH of soil. A soil test will tell you how much lime to add.'
remedy
This ground has been limed, and potatoes want it sour. Scab is skin-deep - the tubers still eat - but where it has been a problem, put the potatoes on ground you have not limed, choose a scab-resistant variety, keep the soil evenly moist for the four to nine weeks after planting while the tubers set, and never lime or add wood ash where potatoes are going next. A later pH reading at or below about 5.2 on this ground would quiet this. We will not give a sulfur rate to get there: the amount needs your lab's buffer pH.
Read the full rule → · open in the planner ↗
The sources agree that potatoes like acid soil, but they don't agree on one number. One source puts the target lower wherever scab keeps coming back, and another explains why: the right number depends on whether your variety resists scab. So Milpa keeps its potato pH range marked as an estimate rather than pretending there's one answer. The same goes for feeding: potatoes are hungry, but how much to add is a question for a soil test, not a guess.
Blight is the other disease that comes back with the crop. Late blight survives the winter in potatoes left in the ground, not in the soil itself:
PromisingLate blight comes back from last year's potatoes, not from the soil: tubers left in the ground carry it through winter as volunteers, so ground that grew potatoes last season needs its volunteers pulled before this year's tomatoes or potatoes go in.
ignored, it still works, just worse · the planner suggests it
Mechanism: Phytophthora infestans needs living tissue to overwinter. Infected tubers left in the ground, in a compost heap that does not freeze, or in a cull pile survive and sprout as volunteers that carry the blight into the new season; tomatoes do not carry it, because frost kills the whole plant and the seed is clean.
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
UMass Extension, 'Late Blight Management for Fall, Winter and Spring', umass.edu/agriculture-food-environment/home-lawn-garden/fact-sheets/late-blight-management-for-fall-winter-spring (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Potato tubers that are infected with late blight and don't freeze or decay during the winter can carry the pathogen over the winter to next spring' - 'Left in the ground at harvest, down several inches in the soil'; 'Disposed of in a compost pile that does not fully decompose and does not freeze'; 'Tomatoes will not carry late blight over the winter, because freezing kills the whole plant'; 'Tomato seed, even from fruit that was infected with late blight, will not carry the pathogen'; 'In the spring (April - June), inspect last year's potato plot and any compost or cull piles for volunteer potato plants that might come up. If you find potato plants, pull them out and put them in the trash or destroy them.'
UMN Extension, 'Late blight of tomato and potato', extension.umn.edu/disease-management/late-blight (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'P. infestans can overwinter in Minnesota if protected in potato cull piles'; 'The host range is typically limited to potato and tomato, but hairy nightshade (Solanum physalifolium) is a closely related weed that can readily become infected'; 'Control volunteer potato plants, as infected plants can grow from infected tubers.'
remedy
From April to June, walk last year's potato ground and any compost or cull pile, pull every volunteer potato and put it in the bin, not the compost. Then plant.
Read the full rule → · open in the planner ↗
Last of all, give the ground a rest from the whole nightshade family:
PromisingDo not plant nightshades in ground that held nightshades within 3 years.
ignored, real yield is lost · the planner warns you
Mechanism: Alternaria solani (early blight) and Septoria lycopersici overwinter on tomato debris and solanaceous weeds; a 2-3 year break plus debris removal starves this inoculum. Fusarium has a very narrow host range, so rotating away from the host is effective. Verticillium is the exception: microsclerotia persist ~10 years and it infects 300+ host families, so a garden-scale rotation does not control it.
Evidence: confirmed against 5 sources in the research-based literature.
the 5 sources
Clemson HGIC, 'Tomato Diseases & Disorders', hgic.clemson.edu/factsheet/tomato-diseases-disorders (read 2026-07-11): 'tomatoes and related vegetables, such as potatoes, peppers, and eggplants, should not be planted on the same land more than once in three years.'
NC State Extension, 'Early Blight of Tomato', content.ces.ncsu.edu/early-blight-of-tomato (read 2026-07-11): 'Rotate every 2-3 years.'
NC State Extension, 'Septoria Leaf Spot of Tomato', content.ces.ncsu.edu/septoria-leaf-spot-of-tomato (read 2026-07-11): 'The fungus is known to overwinter on infected tomato debris and solanaceous weed hosts'; 'Rotate away from tomato for 2 or more years.'
NC State Extension, 'Verticillium Wilt of Tomato and Eggplant', content.ces.ncsu.edu/verticillium-wilt-of-tomato-and-eggplant (read 2026-07-11): 'The pathogen can survive in the soil without a host for up to 10 years in the form of structures called microsclerotia'; 'affects more than 300 host families.'
UMass Extension, 'Solanaceous, Verticillium Wilt', umass.edu/agriculture-food-environment/vegetable/fact-sheets/solanaceous-verticillium-wilt (read 2026-07-11): 'Verticillium wilt tends to affect a wide range of hosts and can infect many unrelated plants. Fusarium spp., on the other hand, have very narrow host ranges.'
remedy
Plant nightshades in different ground, or wait until 3 years have passed since this ground last held them. Clear and remove the old debris either way — the inoculum overwinters on it.
Read the full rule → · open in the planner ↗
Three years without potatoes, tomatoes, peppers, eggplant or tomatillos is the goal. If your beds are too few for that, the crop rotation guide helps you plan around it.
