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.
Sowing depth — an estimate
Soil temperature for germination — an estimate
Frost tolerance — an estimate
Days to maturity — an estimate
Mature height — an estimate
Rules that apply to dill
Alliums and carrot family are unrelated to nightshades/cucurbits/brassicas and can break those families' rotation cycles. They are still not "low-pressure" and need their own rotation. A good hunch
Alliums and carrot family are unrelated to nightshades/cucurbits/brassicas and can break those families' rotation cycles. They are still not "low-pressure" and need their own rotation.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: They host none of the big-three families' soilborne pathogens, so following those crops with an allium or apiaceous crop breaks the host cycle. They are not inherently low-pressure, though. Allium white rot (Sclerotium cepivorum) is allium-specific, its sclerotia persist 15+ years, and it cannot be eradicated once established; apiaceous crops carry their own soilborne diseases.
Evidence: checked against 1 source in the research-based literature.
If you skip this, you lose real yield. The planner warns you.
How it works: The carrot leaf blights (Alternaria dauci, Cercospora carotae and the bacterial blight) and celery's Septoria late blight survive on crop debris and die as it decomposes; a break of two to three years starves them. Alternaria radicina, the black-rot species, infects celery, celeriac, dill, fennel, parsley and parsnip as well, and can persist in soil for up to eight years, which is why the family rotates as one.
Evidence: checked against 5 sources in the research-based literature.
All three pathogens can be transmitted through infected or contaminated seeds and can survive on crop residue, which can act as a source of inoculum in subsequent cropping years.
… a crop should only be grown in the same spot a maximum of once every three years
Remedy
Plant carrot-family crops in different ground, or wait until 3 years have passed since this ground last held them. Either way, remove the old tops or dig them in promptly so they break down, and buy clean seed, because all three carrot blights ride on seed.
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.
A few kinds of seed need light to germinate, and burying them stops them coming up. Sow these on the surface, pressed into firm, moist soil and left uncovered or barely dusted over. Don't sow them at the depth a larger seed would take. Promising
A few kinds of seed need light to germinate, and burying them stops them coming up. Sow these on the surface, pressed into firm, moist soil and left uncovered or barely dusted over. Don't sow them at the depth a larger seed would take.
If you skip this, it still grows, just less well. The planner suggests it.
How it works: These seeds carry the light-sensing pigment phytochrome, which must catch light to switch on the hormone cascade that releases the seed to germinate, so a seed buried past a few millimeters sits in the dark with that switch never thrown and stays dormant.
Evidence: checked against 1 source in the research-based literature.
When sowing light-requiring seeds, sow them on the soil surface
Remedy
Press light-requiring seed onto firmed, moist soil or medium and leave it uncovered or only barely dusted, then keep the surface damp. A seed sitting on top dries out fast, and a fine mist keeps it in place better than a heavy watering. The plant's page says whether it needs light; a seed that needs darkness is the opposite and is covered as usual.
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 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.
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.
