Hardy crops can go in later, counted back from the freeze they can't stand
As recorded: Hardy and half-hardy crops stand a light freeze, so a planting of one has until the date it could still mature before the first night of about 28 °F (-2 °C). Where a night that cold comes in fewer than a quarter of winters, frost closes no window for them.
Promising A person has yet to check it against a source. 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.
What to do about it
Sow or set out hardy crops up to the date the app gives. After it, choose a faster variety or wait for the spring sowing.
The evidence
Evidence: not yet confirmed. It is cited to 8 sources, which a person has yet to read.
What this rests on - 8 pointers
We summarise this source in our notes rather than quote a line from it.
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.
Crops from more-temperate regions can withstand light freezes (28 to 32 degrees Fahrenheit):
If water within the plant cell or between the plant cells freeze, this can result in damage to plant tissue.
Semi-hardy crops tolerate light frost (28–32°F), including beets, carrots, parsnip, lettuce, chard, garden pea (before flowering), Chinese cabbage, endive, radicchio, cauliflower, parsley and celery.
A light frost (32°F) can damage tender plants, while a hard frost (28°F or colder) will kill most warm-season crops.
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.
Frost-freeze probabilities are the likelihood that a given minimum temperature will be experienced at least once during a month or year.
Plus one working note on how the sources were read. Every note is in the data download.
Where this rule stops
It reads the median date of the first 28 °F night at a US station (NCEI 1991-2020) and the share of winters that reach it; abroad the model's cell gives only that share, so a hardy crop there keeps the first 32 °F frost unless the night comes in under a quarter of winters, so one year's cold snap is not seen. Days to maturity are counted at their usual pace; in short, cool days crops grow more slowly, and the extension calendars close later than this count for slow crops and earlier for quick ones. The 28 °F line is where every source's tiers meet; several cole crops stand colder (kale, Brussels sprouts and cabbage to about 24 °F), so for them it is cautious. The calendars disagree: for Houston's cabbage, Texas A&M AgriLife's last optimum date is Sep 20 or Oct 20 and LSU's south Louisiana column runs to Nov 30.
Plants it applies to · 28
Salad & greens · 9, Roots & tubers · 8, Beans & peas · 3, Onions & garlic · 3, Herbs · 3, Flowers · 2
Flowers · 2
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How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
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Cite this page
Milpa Gardens. “Hardy crops can go in later, counted back from the freeze they can't stand.” Evidence grade: Promising. https://milpa.garden/rules/hardy-half-hardy-crops-stand-light-freeze/
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
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- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
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