Do not plant alliums in ground that held alliums within 4 years, and know that the worst allium disease outlasts any rotation.
Promising · costly if ignored → warn
How it works
Fusarium basal rot (Fusarium oxysporum f. sp. cepae) and pink root survive in soil as spores and on other plants' roots, and their inoculum builds where alliums repeat; a four-year break starves them. White rot (Sclerotium cepivorum) is allium-specific and its sclerotia stay viable 15 to 40 years, so rotation reduces but cannot clear it.
What to do about it
Plant alliums in different ground, or wait until 4 years have passed since this ground last held them. If white rot has ever shown here, treat this ground as lost to alliums and grow them elsewhere.
How much it matters: UMass: at least 4 years away from alliums for Fusarium basal rot; Colorado State: onions not more than once every five years, and a rotation under 4 years favours every soil-borne onion disease it covers. White rot: rotation alone does not control it (UMD: sclerotia survive 20-40 years; UMass: 15 years or more).
The evidence
Evidence: confirmed against 4 sources in the research-based literature.
the 4 sources
UMass Extension, 'Alliums, Fusarium Basal Rot', umass.edu/agriculture-food-environment/vegetable/fact-sheets/alliums-fusarium-basal-rot (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Rotate away from alliums for at least 4 years'; 'Fusarium oxysporum f. sp. cepae is a soil-borne pathogen that overwinters as chlamydospores (thick-walled survival spores) buried in the soil'; affects garlic, leeks and onion.
Colorado State University Extension, 'Soil-Borne Diseases of Onion', extension.colostate.edu/resource/soil-borne-diseases-of-onion (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Do not plant onions more than once every five years in a field'; its Table 1 lists a rotation of less than 4 years as favouring damping-off, smut, pink root, Fusarium basal rot and stem and bulb nematode; 'Soil-borne fungal pathogens and nematodes can persist for many years in previously infected onions.'
Univ. of Maryland Extension, 'White Rot of Onion and Garlic', extension.umd.edu/resource/white-rot-onion-and-garlic (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Rotation alone will not control white rot because sclerotia can survive in the soil for 20-40 years'; 'white rot only infects Allium species.'
UMass Extension, 'Alliums, White Rot', umass.edu/agriculture-food-environment/vegetable/fact-sheets/alliums-white-rot (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'White rot survives in soil in the form of sclerotia, which are dense masses of fungal tissue. They may remain viable in soil for 15 years or more without allium hosts.'
Plants this fires on
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- rules: another rule here - alliums rotate on a 4-year interval (verified), the first rotation family outside the big three (O133 step 7, family 1)
Cite this page
Milpa Gardens. "Do not plant alliums in ground that held alliums within 4 years, and know that the worst allium disease outlasts any rotation." Evidence grade: Promising. https://milpa.garden/rules/do-not-plant-alliums-ground-that-held/
A garden-planning corpus: 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.