When to plant celosia 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 celosia 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
Apr 19 – May 3University of Maryland's celosia production guide states seed is sown 4 weeks before the last frost date, which is the only frost-anchored figure found (Minnesota's 10-weeks guidance is anchored to the outdoor planting date, not to frost, so it cannot be used), giving a two-week sowing span opening 4 weeks before the median last freeze. Anchored to the median last spring freeze (May 17). University of Maryland Extension · University of Minnesota Extension · University of Illinois Extension · NC State Extension
Transplant outdoors
May 17 – May 31University of Maryland says to sow or transplant celosia in the field after the danger of frost has passed and NC State places tender annuals after the threat of frost is past, so the window opens at the median last freeze; note Maryland's stricter companion rule of night temperatures consistently above 65 to 70 degrees F is not frost-anchored and cannot be expressed here, so the window's opening day is optimistic in cool-summer areas. Anchored to the median last spring freeze (May 17). University of Maryland Extension · University of Minnesota Extension · University of Illinois Extension · NC State Extension
Direct-sow outdoors
May 17 – May 31The same University of Maryland sentence covers direct sowing — sow or transplant celosia in the field after the danger of frost has passed — so direct sowing opens at the median last freeze, with Illinois independently classing celosia a tender annual. Anchored to the median last spring freeze (May 17). University of Maryland Extension · University of Minnesota Extension · University of Illinois Extension · NC State Extension
Variety assumption: Assumes Celosia argentea in its crested (cockscomb) and plumed forms; Maryland warns that exposure below 60 degrees F stunts plants and triggers premature flowering, so the frost-anchored window opens earlier than the temperature at which celosia actually thrives.
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 (4)
- University of Maryland Extension: Production of Celosia as a Cut Flower (accessed 2026-07-25)"Sow Celosia 4 weeks before the last frost date."
- University of Minnesota Extension: Celosia (accessed 2026-07-25)"Celosia seeds can be started indoors about 10 weeks prior to the anticipated outdoor planting date."
- University of Illinois Extension: Celosia — Flowers (accessed 2026-07-25)"Tender Annual"
- NC State Extension: Extension Gardener Handbook, Ch. 10: Herbaceous Ornamentals (accessed 2026-07-25)"Hardy annuals are the most cold-tolerant. They tolerate light frost and some freezing weather without being killed. In most cases, hardy annuals are planted in the fall or in the spring before the last frost date."