Do not plant legumes in ground that held legumes within 3 years
Do not plant legumes in ground that held legumes within 3 years; the root rots build where they repeat, and the worst of them outlast any garden rotation.
Promising A person has checked it against its sources. If you skip this, you lose real yield. The planner warns you.
How it works
Bean and pea root rots (Fusarium solani, Rhizoctonia, Pythium, Aphanomyces) and white mold (Sclerotinia sclerotiorum) survive in soil as spores and sclerotia and build where legumes follow legumes; a three-year break holds the common ones down. Fusarium needs longer, and Aphanomyces oospores and white mold's sclerotia persist for many years, so rotation reduces but cannot clear them.
What to do about it
Plant legumes in different ground, or wait until 3 years have passed since this ground last held them. Where root rot has shown, make it longer, and keep the ground draining freely, because every one of these rots is worse in wet soil.
How much it matters: Cornell's rotation table: beans root rots 3 years, white mold 3, anthracnose 2; peas root rots 3-4, Fusarium wilt 4-5. UMN: more than 3 years away from legumes, and more than 6 for Fusarium. UConn: 7 years for white mold. NDSU: pulses in close rotations every 2-3 years are at greatest risk.
The evidence
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
We summarise this source in our notes rather than quote a line from it.
Rotate away from legumes for more than 3 years
Fields with a long history of pulses in close rotations (every 2-3 years) are at greatest risk
Plants it applies to · 14
Beans & peas · 9, Cover crops & soil builders · 5
Cover crops & soil builders · 5
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How this rule has changed
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- Added to the rules
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Milpa Gardens. “Do not plant legumes in ground that held legumes within 3 years; the root rots build where they repeat, and the worst of them outlast any garden rotation.” Evidence grade: Promising. https://milpa.garden/rules/do-not-plant-legumes-ground-that-held/
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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.
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- 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.