Celery

UMass Extension, 'Carrot, Alternaria Leaf Blight', umass.edu/agriculture-food-environment/vegetable/fact-sheets/carrot-alternaria-leaf-blight (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Practice relatively long rotations of 3-4 years'; 'A. radicina infects celery, celeriac, caraway, dill, fennel, parsley, and parsnips'; 'The fungus survives in the soil on crop debris but dies when the residue decomposes'; A. radicina 'can persist in soil for up to 8 years.'

Cornell Vegetables, 'Carrot Leaf Blight Diseases and their Management', vegetables.cornell.edu/pest-management/disease-factsheets/carrot-leaf-blight-diseases-and-their-management (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'it is important to practice a minimum of a 2-year rotation out of carrots to allow time for decomposition of crop residue'; '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.'

Cornell Vegetables, 'Do Rotations Matter within Disease Management Programs?', vegetables.cornell.edu/pest-management/disease-factsheets/do-rotations-matter-within-disease-management-programs (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): its rotation table gives carrot leaf blights (fungal and bacterial) 2-3 years and celery leaf blights 2 years.

UMass Vegetable Notes 2025 vol. 37:13, Septoria late blight of celery, umass.edu/agriculture-food-environment/vegetable/newsletters/vegetable-notes/vegetable-notes-2025-vol-3713 (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'The pathogen survives in crop debris in soil for up to 18 months, or outbreaks may originate from seed-borne inoculum.'

Clemson HGIC, 'Crop Rotation', hgic.clemson.edu/factsheet/crop-rotation (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'a crop should only be grown in the same spot a maximum of once every three years'; its family table puts carrot, parsley, celery, cilantro, fennel and dill in the parsley family (Apiaceae).

University of Illinois Extension, 'Time Your Vegetable Plantings by Cold Hardiness' (2018-03-26), extension.illinois.edu/blogs/ilriverhort/2018-03-26-time-your-vegetable-plantings-cold-hardiness: very hardy vegetables 'withstand freezing temperatures and hard frosts without injury' (planted earliest in spring); frost-tolerant vegetables 'can withstand light frosts, but not freezing temperatures' (planted a couple of weeks later). LLM-summarised from a read of the page; it establishes the CATEGORIES but states no week offsets.

Colorado State Univ. Extension, GardenNotes #720, 'Vegetable Planting Guide', extension.colostate.edu/resource/vegetable-planting-guide (read 2026-07-25): hardy vegetables go in 'As early as 2-4 weeks before the date of the average last spring frost'; semi-hardy 'As early as 0-2 weeks before the date of the average last spring frost'; tender from seed 'around the date of the average last spring frost'; very tender 'Typically 2+ weeks after'. This is the source that states the offsets in weeks.

Where this rule sits in that range: hardy at 3 weeks is mid-range of CSU's 2-4. Half-hardy at 2 weeks is the EARLIEST EDGE of CSU's 0-2 - the most aggressive planting CSU sanctions, not the middle of it. The rule is inside published guidance at both ends, but it leans early on the half-hardy side and a gardener following it in a cold spring is taking that boundary.

Do not import an offset from another publication's hardiness scheme without checking the category names: CSU has no 'very hardy' tier, so a '4-6 weeks before frost' figure written against a four-tier scheme does not describe CSU's 'hardy'. Categories are not comparable across sources.