Do not plant the carrot family in ground that held it within 3 years.
Promising A person has checked it against its sources. If you skip this, you lose real yield. The planner warns you.
How it works
The carrot leaf blights (Alternaria dauci, Cercospora carotae and the bacterial blight) and celery's Septoria late blight survive on crop debris and die as it decomposes; a break of two to three years starves them. Alternaria radicina, the black-rot species, infects celery, celeriac, dill, fennel, parsley and parsnip as well, and can persist in soil for up to eight years, which is why the family rotates as one.
What to do about it
Plant carrot-family crops in different ground, or wait until 3 years have passed since this ground last held them. Either way, remove the old tops or dig them in promptly so they break down, and buy clean seed, because all three carrot blights ride on seed.
How much it matters: UMass: 3-4 years for carrot Alternaria leaf blight; Cornell's rotation table: carrot leaf blights 2-3 years, celery leaf blights 2 years; Clemson: three years the minimum for any family.
The evidence
Evidence: checked against 5 sources in the research-based literature.
The 5 sources
All three pathogens can be transmitted through infected or contaminated seeds and can survive on crop residue, which can act as a source of inoculum in subsequent cropping years.
We summarise this source in our notes rather than quote a line from it.
The pathogen survives in crop debris in soil for up to 18 months, or outbreaks may originate from seed-borne inoculum.
… a crop should only be grown in the same spot a maximum of once every three years
Plants it applies to · 8
Herbs · 5, Roots & tubers · 2, Salad & greens · 1
Salad & greens · 1
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Wording made clearer
- Added to the rules
More ways Milpa can help
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Cite this page
Milpa Gardens. “Do not plant the carrot family in ground that held it within 3 years.” Evidence grade: Promising. https://milpa.garden/rules/do-not-plant-carrot-family-ground-that/
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.