A warm-season bean germinates from warm soil, whatever the calendar says
A warm-season bean germinates from warm soil, whatever the calendar says. Sown into cold ground it rots or emerges weak, even after the frost has passed.
Promising A person has checked it against its sources. If you skip this, it still grows, just less well. The planner suggests it.
How it works
Warm-season legumes take up water fast at sowing (imbibition), and in cold soil that first rush of cold water injures the seed tissue before the seedling can establish (imbibitional chilling), so the seed rots or comes up damaged. Soil below about 15 °C (60 °F) at sowing depth is where this bites, and the frost-free date can arrive weeks before the soil is that warm.
What to do about it
Wait for the soil to warm to about 15 °C (60 °F) at sowing depth, which a soil thermometer reads in a minute, or start the beans in warm cells and set them out. Peas are the opposite and are out of scope here. Half-hardy, they germinate in cold soil and are sown early on purpose.
How much it matters: No date or yield figure is given, because soil warms on its own schedule at each site. The rule advises checking the soil, whatever the calendar says; it never blocks, because a gardener with warm ground or warm cells is right to sow.
The evidence
Evidence: checked against 2 sources in the research-based literature.
The 2 sources
Beans are warm weather vegetables that require soil and air temperatures above 60°F for best germination and plant growth
Bean seed planted in cold soil may rot rather than germinate, and plant growth will be very slow in cooler weather
Plants it applies to
Read next
- Growing beans: pole or bush, and what the roots leave behindThe same bean is a knee-high bush or an all-season climbing vine, and the packet says which. How to grow both, and the truth about the nitrogen everyone repeats.
- Cold frames and low tunnels for extra weeks of seasonWhat cold frames, low tunnels and row covers really buy: the degrees, the weeks, and the venting chore that decides everything. Plus what to grow under each.
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Details updated
- Wording made clearer
- Details updated
- A person read the sources and confirmed it
- Added to the rules
Cite this page
Milpa Gardens. "A warm-season bean germinates from warm soil, whatever the calendar says. Sown into cold ground it rots or emerges weak, even after the frost has passed." Evidence grade: Promising. https://milpa.garden/rules/warm-season-bean-germinates-from-warm-soil/
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- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
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- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
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