When to plant calendula in Boise, Idaho
May 3 – May 17
Direct-sow 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. Direct-sow calendula 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
Direct-sow outdoors
May 3 – May 17Colorado State University Extension asterisks calendula in its seed-starting table to flag it as a plant best suited to direct seeding in the garden rather than an indoor start, and its footnote places that sowing two weeks prior to the average frost-free date, which UW-Madison corroborates by saying seed can be sown directly in the garden just before the last frost date, so the window runs from 14 days before the last-frost date to the last-frost date itself. Anchored to the median last spring freeze (May 17). Colorado State University Extension · University of Wisconsin-Madison Division of Extension
Start seeds indoors
Not calculatedNo indoor-start window is encoded because CSU's asterisk flags calendula as best suited to direct seeding rather than an indoor start, and that flag is followed here in preference to the 6-to-8-week indoor sowing UW-Madison mentions only as an option for earlier bloom.
Transplant outdoors
Not calculatedNo transplant window is encoded because neither source gives a frost-relative date for setting calendula plants out in the garden.
Fall planting
Not calculatedNo source-backed fall planting rule exists for this crop in the registry, so no fall window is calculated.
Variety assumption: Covers Calendula officinalis (pot marigold / English marigold), a hardy annual distinct from the Tagetes marigolds encoded under the separate 'marigold' entry; CSU's 4-week cold-frame and 4-week indoor columns for calendula are not encoded because the same row's asterisk marks the plant as better suited to direct seeding.
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 (2)
- Colorado State University Extension: Growing Annual Plants from Seed (accessed 2026-07-25)"*Plants best suited for direct seeding in garden two weeks prior to the average frost-free date."
- University of Wisconsin-Madison Division of Extension: Calendula, Calendula officinalis – Wisconsin Horticulture (accessed 2026-07-25)"Seeds can be sown directly in the garden just before last frost date, but for earlier bloom start seeds indoors about 6 to 8 weeks before last frost."