Not every potato grows the same. These are its main types (its cultivar groups), and the planner sizes, times and supports each one by its own numbers.
First early potato (New potatoes) — bush, spacing in row 30 cm12 in, mature height 40–50 cm16–20 in, mature spread 40–50 cm16–20 in, days to maturity 49–56
Second early potato — bush, spacing in row 35 cm14 in, mature height 45–55 cm18–22 in, mature spread 45–55 cm18–22 in, days to maturity 90–110
Maincrop potato (storage) — bush, spacing in row 38 cm15 in, mature height 50–60 cm20–24 in, mature spread 50–60 cm20–24 in, days to maturity 110–135
Numbers we’re less sure of
Many of our estimates come from an extension page we’ve read that gets close without pinning the number down. Others are still our own best guess, and on some the sources disagree. Treat them all as a starting point.
Soil pH (in water) — an estimate
First early potato (New potatoes): mature height — an estimate
First early potato (New potatoes): mature spread — an estimate
Second early potato: mature height — an estimate
Second early potato: mature spread — an estimate
Second early potato: days to maturity — an estimate
Maincrop potato (storage): mature height — an estimate
Maincrop potato (storage): mature spread — an estimate
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Maincrop potato (storage): days to maturity — an estimate
First early potato (New potatoes): spacing in row — an estimate
Second early potato: spacing in row — an estimate
Maincrop potato (storage): spacing in row — an estimate
Days to maturity — an estimate
Mature spread — an estimate
Monthly temperatures it grows in — an estimate
Mature height — sources disagree
Rules that apply to potato
Don't plant nightshades where nightshades grew in the last 3 years Promising
Don't plant nightshades where nightshades grew in the last 3 years
If you skip this, you lose real yield. The planner warns you.
How it works: 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. Its microsclerotia persist ~10 years and it infects 300+ host families, so a garden-scale rotation does not control it.
Evidence: checked against 5 sources in the research-based literature.
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, because the inoculum overwinters on it.
Don't plant anything sensitive to walnut toxin (juglone) within a walnut tree's root zone. Nightshades are sensitive, and so are apple and cabbage. Well established
Don't plant anything sensitive to walnut toxin (juglone) within a walnut tree's root zone. Nightshades are sensitive, and so are apple and cabbage.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: Common scab (Streptomyces scabies) infects young tubers through the lenticels and is favored 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: checked against 5 sources in the research-based literature.
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 and 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, because the amount is your lab's to give: ask it for its sulfur recommendation for your soil.
Late blight comes back from last year's potatoes. It does not come back 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. Promising
Late blight comes back from last year's potatoes. It does not come back 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.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: 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: checked against 2 sources in the research-based literature.
P. infestans can overwinter in Minnesota if protected in potato cull piles
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. Don't compost it. Then plant.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: Resource concentration. A specialist locates and holds its host more efficiently at higher host density and continuity, so an unbroken run of one family across adjacent beds is an easier target than the same family separated by a non-host (associational resistance).
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards (Brassica oleracea) Root 1973
… the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments.
Flea beetle movement in a broccoli monoculture and diculture Elmstrom, Andow & Barclay 1988
… strong, direct support for the hypothesis that host plants are harder to find and easier to lose in vegetationally diverse habitats than in monocultures.
Remedy
Where one family fills adjacent beds in a single season, breaking the run with a non-host family between them lengthens the distance the specialist must travel to the next host. The app discloses this and never docks a score. A continuous single-family block can be the right call anyway (a wind-pollinated crop like corn sets better massed), so the app names the trade-off and leaves the choice to the gardener.
Cold-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. Promising
Cold-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.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: 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: checked against 2 sources in the research-based literature.
Potato 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. Promising
Potato 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.
This one is about eating safely, not how the plant grows. The planner suggests it.
How it works: 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: checked against 2 sources in the research-based literature.
Green skin occurs when potato tubers experience exposure to light
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 defense is to keep light off the tubers in the first place, in the ground and again in dark storage.
Potatoes are grown from certified seed potatoes (disease-free seed tubers from a certified source). Don't plant 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. Promising
Potatoes are grown from certified seed potatoes (disease-free seed tubers from a certified source). Don't plant 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.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: Potato is propagated vegetatively (the crop grows from a piece of tuber), 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: checked against 2 sources in the research-based literature.
When buying seed tubers, ask for certified seed as this will help reduce the potential for introducing disease into the garden
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).
Brown leaf spots with target-like rings, starting on the lower leaves of tomato or potato, are early blight, a fungus that overwinters in plant debris and soil and reaches the leaves by soil splash. Promising
Brown leaf spots with target-like rings, starting on the lower leaves of tomato or potato, are early blight, a fungus that overwinters in plant debris and soil and reaches the leaves by soil splash.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: The early blight fungi overwinter in infected plant debris and in the soil. Lower leaves are infected when they touch contaminated soil or when rain splashes soil up onto them; the spores need free water or very high humidity to germinate. Spots enlarge with concentric rings, and fruit can form leathery black spots.
Evidence: checked against 1 source in the research-based literature.
Mulch the soil under the plants and stake them, to keep soil and leaves apart; water at the base and keep it off the leaves. Remove spotted leaves early, but no more than a third of the plant. Grow resistant varieties (often marked EB), rotate out of tomatoes and their relatives for at least two years, and remove or bury infected plants in the fall.
If you skip this, the planting fails. The planner warns you.
How it works: On a clear, still night leaves lose heat to the open sky, so a leaf can fall to freezing and ice can form in it while the thermometer, a couple of meters up, still reads a few degrees above.
Evidence: checked against 7 sources in the research-based literature.
Frost occurs when air is warmer than 32°F but plant tissues drop to 32°F or below because plants radiate (lose) heat into the atmosphere, especially during cool, clear nights.
Radiation frosts occur on calm clear nights that lack cloud cover to hold in heat.
Remedy
The evening before, cover the crops at risk with a sheet or frost cloth, never plastic, reaching the ground and loose at the bottom so the soil's warmth can rise under it, and take it off in the morning. A cover helps least in a long, hard freeze.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: Soil warmed by the sun by day is the heat source at night; a covering low to the ground traps that heat around the plants on calm, clear nights, keeping them a few degrees above the open air through the light frosts at each end of the season.
Evidence: checked against 6 sources in the research-based literature.
The ground and frame of the cold frame are heated by the sun during the day and radiate that heat during the night, keeping the inside warmer. They are used to extend the growing season by two to four weeks in both the fall and the spring, allowing you to start plants outdoors earlier and continue growing them later in the season.
In trials in Fort Collins, Colorado, a plastic cover on a frame typically provides 3°F to over 6°F of frost protection. It works well for cool season crops that are somewhat tolerant of frosty nights and adds two to six weeks or more on both ends of the growing season.
Soil warmed by the sun in the daytime, is the source of heat for frost protection at night. Moist, smooth soil absorbs more heat. To trap heat from the soil around young vegetables at night, place a covering that is low to the ground and spreading. To recharge the heat source for the next night, any covering must allow sunlight to shine through to the soil or must be removed in the daytime.
Low = Plant 1–2 weeks before suggested planting date; Medium = 2–4 weeks before suggested planting date; High = 4–8 weeks before average planting date
hort.extension.wisc.edu
Floating Row CoverUniversity of Wisconsin-Madison Extension, Wisconsin Horticulture, Susan Mahr
Depending on the weight of the covering you choose, you can gain between 2 and 8 degrees of frost protection or warm the local environment sufficiently to harvest certain crops a week or two early.
Clear plastic is useless in providing frost protection because the radiant energy released from the soil on those frosty nights passes right through the covering and never warms the air around the plants.
Remedy
Sow or set out cool-season crops under the cover that many weeks ahead of the open-ground date, and keep autumn crops covered past the usual last call. Vent on sunny days, keep plastic off the leaves, and close the cover before sunset.
If you skip this, you lose real yield. The planner suggests it.
How it works: A crop grows and makes its harvest within a band of warmth: in months colder than its band it grows too slowly to finish, and in months hotter than it a cool-season crop bolts and turns bitter while a warm-season crop drops its flowers.
Evidence: checked against 9 sources in the research-based literature.
Hold the Tomatoes!UC Master Gardeners of Monterey, San Benito and Santa Cruz Counties, Jazmin Lopez
Average monthly temperatures for cool-season crops during their growing period: 60-65F. This includes, carrots, parsnips, spinach, lettuce, broccoli, and garlic to name a few.
Group D: These vegetables thrive in areas where the mean monthly temperatures range between 15 and 18°C. They are intolerant to temperatures between 21 and 24°C, and tolerate weak frosts. This group includes spinach, lettuce, broccoli, beetroot, Brussels sprout, cabbage, radish, rhubarb and watercress.
In the Top End climate lettuce plantings are restricted to the cooler months from April till July. Hot weather makes the plants to bolt, as they do not form a head but flower instead.
If you skip this, you lose real yield. The planner warns you.
How it works: A hardy or half-hardy crop's tissue survives the ice of a light freeze down to about 28 °F (-2 °C), so its season ends at the first night that cold, which comes after the first 32 °F frost, and later still where winters are mild.
Evidence: not yet confirmed. It is cited to 8 sources, which a person has yet to read.
Tender crops will be damaged or destroyed by a light frost, semi-hardy crops can tolerate temperatures in the upper 20s°F, and hardy crops will survive temperatures in the mid to low 20s°F.
This temperature threshold kills some types of commercial crops and residential plants, while temperatures below 28°F for an extended period of time can kill most types of commercial crops and residential plants.
If you skip this, you lose real yield. The planner suggests it.
How it works: A crop grows at the pace its days to maturity assume only in months at least as warm as the low end of its band, and in cooler months it grows too slowly to finish, so a frost-free season of cool months can end before the crop is ready.
Evidence: not yet confirmed. It is cited to 8 sources, which a person has yet to read.
Hold the Tomatoes!UC Master Gardeners of Monterey, San Benito and Santa Cruz Counties, Jazmin Lopez
Average monthly temperatures for warm season crops during their growing period: 65-80F. This includes melons, corn, eggplant, peppers, squash, and tomatoes.
Eggplant needs warm conditions, and will not thrive during a cool season. There are varieties available that thrive in Minnesota’s short summer season.
Most seed packets and variety descriptions in catalogs estimate the days from planting to maturity. Add about 10 days to this estimate because of the cooler, shorter days in the fall.
Plus one working note on how the sources were read.
Remedy
Grow it under cover, in a greenhouse, tunnel or cloche; start it early indoors and choose its quickest variety; or grow a crop whose months these are.
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
