On ground that has carried brassicas within the rotation interval
On ground that has carried brassicas within the rotation interval, a measured soil pH below about 7.2 leaves clubroot's door open; raising it is the lever every clubroot guide we read names, and the direction is all we give.
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
Plasmodiophora brassicae's resting spores germinate in wet soil below about pH 7.0, and alkaline soil with high calcium suppresses the infection; liming to 7.1 to 7.5 slowly reduces severity but is not reliable once an infestation is established.
What to do about it
Raise this ground's pH toward 7.2 with lime well ahead of planting, using calcitic lime unless your magnesium is low (then dolomitic), and watch for boron shortage on coarse soils once the pH is up. Your lab gives the amount of lime, from a lime requirement test of your soil, and we don't. Rotation stays the first lever; this is the second.
The evidence
Evidence: checked against 4 sources in the research-based literature.
The 4 sources
The pathogen germinates in wet soils when the soil temperature is between 18 and 25 ºC (64 to 77 F), and the soil pH is acidic (pH less than 7.0)
Maintain soil pH at 7.0-7.2 where clubroot is a concern. Lime well ahead of planting and incorporate thoroughly
It is essential that hydrated lime be added each year unless the soil pH exceeds 7.5
Plants it applies to · 8
Roots & tubers · 4, Salad & greens · 3, Flowers · 1
Roots & tubers · 4
Salad & greens · 3
Flowers · 1
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Sources updated
- Details updated
- Wording made clearer
- Added to the rules
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Cite this page
Milpa Gardens. “On ground that has carried brassicas within the rotation interval, a measured soil pH below about 7.2 leaves clubroot's door open; raising it is the lever every clubroot guide we read names, and the direction is all we give.” Evidence grade: Promising. https://milpa.garden/rules/ground-that-has-carried-brassicas-within-rotation/
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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.