Where frost sets the season
Where frost sets the season, a warm crop waits for warm ground and still needs enough warm months to reach harvest.
As recorded: Where frost sets the season, a frost-tender crop goes in once the ground is warm, not only once frost has passed: not before its place's monthly mean temperature reaches 15.6 °C (60 °F), the soil warmth its sources give for planting warm-season crops. Where frost sets the season, a crop reaches harvest outdoors only where enough months in a row average at least its lowest monthly temperature to cover its days to maturity. Where fewer do, or none, it is a crop to grow with care: under cover, from an early start indoors, or as its quickest variety.
A good hunch A person has yet to check it against a source. If you skip this, you lose real yield. The planner suggests it.
How it works
Warm-season seed is slow to sprout and can rot in soil cooler than about 60 °F (15.6 °C), and a transplant stands still in it, so where spring warms slowly a crop planted at the last frost sits in cold ground for weeks. 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.
What to do about it
Wait for the warm day, or warm the soil first under a cloche or black plastic; 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.
The evidence
Evidence: not yet confirmed. Of its 19 sources, a person has read 9, and the rest wait for a read.
What this rests on - 19 pointers
… 65-75º 60º 90º Cucumber, cantaloupe
Average monthly temperatures for warm season crops during their growing period: 65-80F. This includes melons, corn, eggplant, peppers, squash, and tomatoes.
Of the warm season vegetables, bush beans and summer squash are the most likely to succeed.
Eggplant needs warm conditions, and will not thrive during a cool season. There are varieties available that thrive in Minnesota’s short summer season.
In general, smaller-fruited peppers are more tolerant of both cool and hot temperatures
Cold rain, wind, and cool nights can keep coastal soils cold well into summer.
There are some things you can’t do very well on the coast, like tomatoes,
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.
Soil temperature conditions for vegetable seed germination (in degrees F)
They need daytime temperatures above 60°F, and prefer temperatures of 70°F to 95°F. A week of daytime temperatures below 55°F may stunt the crop.
Seeds germinate best when soil temperatures are close to 60 degrees Fahrenheit. Use a soil thermometer to be sure the soil is warm enough.
Plant beans once the soil has warmed. In much of Minnesota, this is not until late May or even early June.
Sow seed directly in the garden after the soil has warmed, in late May to early June.
Transplant outdoors after all danger of frost has passed and the soil has warmed.
Seeds need a soil temperature above 10°C (50°F) to germinate, so wait until late spring or early summer.
French beans can be sown outdoors once all risk of frost has passed and the soil is warming up – usually in late May or early June, depending on your local climate.
You can sow seeds outdoors in late May or early June, once the soil warms up.
Ideally, tomatoes should not be planted out into the garden until the soil temperature reaches a minimum of 16 degrees, and 18-20 degrees is even better. Make sure you plant after the latest chance of frost, eg. In cold areas this is usually the first week of November.
Once the danger of frosts has passed and the ground is warming. Generally October/November.
Plus one working note on how the sources were read. Every note is in the data download.
Where this rule stops
It reads each month's normal mean, the average of its normal daily high and low, so a warm summer, a sheltered wall or a cold snap is not seen. Its crop limits come from one table that does not say what its numbers measure; they are read as monthly averages, so its verdict is an estimate. Away from a weather station the model's monthly highs run cooler than the towns' own, so it can read a place's summer cooler than it is. Days to maturity are counted at their usual pace, and cool months slow a crop down. Its planting line is a soil temperature read against the air's normal monthly mean, because no place here carries a soil temperature and no source read says how one follows the other; its day is an estimate. Sunny soil warms ahead of the air, so in a sunny spring the day can come later than a soil thermometer would say.
Plants it applies to · 36
Fruiting vegetables · 12, Salad & greens · 10, Roots & tubers · 6, Beans & peas · 4, Onions & garlic · 2, Herbs · 2
Fruiting vegetables · 12
+4 moreShow fewer
Salad & greens · 10
Beans & peas · 4
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Details updated
- A person read the sources and confirmed it
- Sources updated
- Details updated
- Added to the rules
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Milpa Gardens. “Where frost sets the season, a warm crop waits for warm ground and still needs enough warm months to reach harvest.” Evidence grade: A good hunch. https://milpa.garden/rules/where-frost-sets-season-frost-tender-crop/
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