Beans that bloom in the hottest weeks drop their flowers.
As recorded: A bean sowing that comes ready in a month whose normal daytime high is 90 F (32 C) or more is likely to drop its flowers and set few pods.
Promising A person has checked it against its sources. If you skip this, you lose real yield. The planner warns you.
How it works
Above about 90 °F the pollen turns sticky and pollination fails, so the flowers fall without setting pods.
What to do about it
Sow so the beans bloom before the hottest weeks, or wait and sow for fall once the hottest month has passed. Keep the soil from drying out while they bloom.
The evidence
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
This condition occurs when the temperature is over 90°F, the soil moisture is low, or smog is present during the blossoming period.
When nights are hot-above 75 degrees or too cool below 55, fruit won’t set and blooms fall off. This is also a problem when day temperatures rise above 90.
Flower abortion can happen at temperatures ranging from 75°F to 95°F.
Planting guide for Florida vegetables
Where this rule stops
It reads the normal high of the month the crop comes ready, standing in for bloom a few weeks earlier, so it cannot see a heat wave in a mild month. Dry soil makes the drop worse; it does not read soil moisture.
Common beans only (bush and pole); lima and runner beans and cowpeas are not covered. 90 °F is UC IPM's and NC State's figure; UMN puts green beans' flower drop over 95 °F, so 90 is the cautious line. NC State's hot-night figure (above 75 °F) is not used: against UF/IFAS's calendar it paused nothing in Florida. The line rides the trigger in the sources' own Fahrenheit and is compared against the Celsius normals converted, unrounded.
Plants it applies to
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Added to the rules
Cite this page
Milpa Gardens. "Beans that bloom in the hottest weeks drop their flowers." Evidence grade: Promising. https://milpa.garden/rules/bean-sowing-that-comes-ready-month-whose/
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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.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.