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
Days to germinate — an estimate
Frost tolerance — an estimate
Days to maturity — an estimate
Spacing in row — an estimate
Mature spread — an estimate
Rules that apply to French marigold
Don't sow or set out tender crops before your last frost date Well established
Don't sow or set out tender crops before your last frost date
If you skip this, the planting fails. The planner won’t allow it.
How it works: The season's accumulated growing degree days (a running total of its warmth) against the total the crop needs to mature, or the crop's days to maturity against the number of frost-free days.
Evidence: checked against 3 sources in the research-based literature.
Once you know the average dates of the last frost in spring and the first frost in fall, count the number of days between. If the “days to maturity” figure for a desired vegetable is a larger number of days and the “frost tolerance” column indicates “none,” the sad truth is that particular vegetable probably won’t grow to maturity.
… high elevation areas don’t accumulate enough “growing degree units” (GDUs, also called growing degree days and heat units) to support some of the most coveted warm season vegetables
Remedy
Start it indoors and transplant it, choose a variety with fewer days to maturity, or skip this crop at this site.
Do not plant lettuce or its family in ground that held it within 3 years, and know that lettuce drop's fungi live on most other vegetables too. A good hunch
Do not plant lettuce or its family in ground that held it within 3 years, and know that lettuce drop's fungi live on most other vegetables too.
If you skip this, you lose real yield. The planner suggests it.
How it works: Bottom rot (Rhizoctonia solani) and lettuce drop (Sclerotinia sclerotiorum and S. minor) survive in soil as mycelium and sclerotia for years and build where lettuce repeats; a three-year break holds bottom rot down. Drop's fungi infect alliums, brassicas, nightshades, cucurbits and legumes as well, so a lettuce rotation slows them without starving them, and only cereals are safe ground.
Evidence: checked against 4 sources in the research-based literature.
Sclerotinia sclerotiorum and S. minor have a wide host range infecting allium (onion, garlic), brassica (cabbage, broccoli), solanaceae (pepper, potato), cucurbits (cucumber, squash), lettuce, and sweetpotato crops
Rhizoctonia survives in the soil, as mycelium or sclerotia
Remedy
Plant lettuce and its family in different ground, or wait until 3 years have passed since this ground last held them. Where drop has shown, the break that counts is one of grains or corn, since most vegetables carry it, and dead plants go in the bin. Keep them out of the compost, because the sclerotia survive it.
The planner won’t plan around this claim. What is known instead is below.
What is known: Tagetes patula suppresses Meloidogyne spp. via alpha-terthienyl and related thiophenes. Suppression requires a dense sole-crop stand held for a full season, i.e. a biofumigant cover crop. Scattered marigolds among vegetables do approximately nothing.
Evidence: checked against 1 source in the research-based literature.
Does marigold have an effect on plant-parasitic nematodes when grown in an intercropping setting? Probably not.
Marigolds do suppress root-knot nematodes, but only as a solid stand grown for a full season as a cover crop. Dotting them between your tomatoes will not do it.
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.
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.
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.
