When to plant celeriac in Boise, Idaho
May 17 – May 31
Transplant outdoors · typical Boise yearClimate basis: NOAA station Boise 7 N, ID (USC00101017), 6 mi (9 km) from downtown Boise (ZCTA 83702 centroid), elevation 3885 ft, on the 1991–2020 climate normals. Transplant celeriac outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 17). One year in ten still freezes after June 10.
The Boise year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Jun 10
Every method, with its sources
Start seeds indoors
Mar 8 – Mar 22The UC Master Gardener Program of Sonoma County (University of California Cooperative Extension) says to "Sow seed indoors as early as 10 weeks before the average last frost date in spring," so the sowing span opens ten weeks before the last frost and runs two weeks; no competing extension figure was found, so this stands without reconciliation. Anchored to the median last spring freeze (May 17). University of California Cooperative Extension, UC Master Gardener Program of Sonoma County
Transplant outdoors
May 17 – May 31The same UC Master Gardener page states plants "can go into the garden 10-12 in. apart on the average date of last frost," a point rule that opens a 14-day transplanting span at the last frost date; the page's alternative air- and soil-temperature condition is not frost-anchored and was therefore not encoded. Anchored to the median last spring freeze (May 17). University of California Cooperative Extension, UC Master Gardener Program of Sonoma County
Variety assumption: Assumes a standard 100-to-120-day celeriac variety grown from transplants; germination is slow, so the long indoor lead time is part of the published rule rather than an added buffer.
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (1)
- University of California Cooperative Extension, UC Master Gardener Program of Sonoma County: Celeriac (accessed 2026-07-25)"Sow seed indoors as early as 10 weeks before the average last frost date in spring."