Do not plant brassicas in ground that held brassicas within 4 years
Do not plant brassicas in ground that held brassicas within 4 years (extension recommends 4-7, and even that is not a cure).
As recorded: Do not plant Brassicaceae in ground that held Brassicaceae within 4 years (extension recommends 4-7, and even that is not a cure).
Promising A person has checked it against its sources. If you skip this, you lose real yield. The planner warns you.
How it works
Plasmodiophora brassicae forms thick-walled resting spores that survive in soil more than 10 years. They germinate in wet, acidic soil (pH < 7); liming above ~7.2 suppresses infection. Spores outlast any garden rotation, so a host-free break reduces but does not clear inoculum.
What to do about it
Plant brassicas in different ground, or wait at least 4 years (extension recommends 4 to 7). Rotation alone is not a cure, because the resting spores outlast it. Raising soil pH above ~7.2 suppresses infection.
How much it matters: Extension recommends long rotations away from brassicas: 4-7 years (NC State), 5-7 (UMass), "at least 7 years" (Cornell). It also notes this is "not guaranteed to prevent disease." The realistic levers are soil pH (lime to >7.2) and resistant cultivars; rotation is complementary.
The evidence
Evidence: checked against 3 sources in the research-based literature.
The 3 sources
Infested fields should be rotated away from brassica for a minimum of 4-7 years, but this is not guaranteed to prevent disease
… rotation of at least 7 years out of susceptible crucifers may be effective.
Plants it applies to · 8
Roots & tubers · 4, Salad & greens · 3, Flowers · 1
Roots & tubers · 4
Salad & greens · 3
Flowers · 1
Folklore it answers
Read next
- Do you need to rotate crops in a raised bed?Yes. The pests and diseases live in the soil, so a raised bed needs rotating like any ground. Here's why, and why digging out the soil is the costly way to do the same job.
- Crop rotation for the home gardenMove crops by plant family so soil-borne pests and diseases can't settle in. What to rotate, how far apart, and what rotation can and can't do.
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Sources updated
- Wording made clearer
- Advice on what to do added
- A person read the sources and confirmed it
- Added to the rules
You must rotate every crop to new ground every single year. · What can I plant now?
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Cite this page
Milpa Gardens. “Do not plant brassicas in ground that held brassicas within 4 years (extension recommends 4-7, and even that is not a cure).” Evidence grade: Promising. https://milpa.garden/rules/do-not-plant-brassicas-ground-that-held/
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
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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.