When to plant sunflower in Billings, Montana
May 10 – May 24
Transplant outdoors · typical Billings yearClimate basis: NOAA station Billings Wtp, MT (USC00240802), 13 mi (21 km) from downtown Billings (ZCTA 59101 centroid), elevation 3097 ft, on the 1991–2020 climate normals. Transplant sunflower outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 10). One year in ten still freezes after May 24.
The Billings year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to May 24
Every method, with its sources
Start seeds indoors
Apr 19 – Apr 26Illinois Extension's '2-3 weeks before planting outdoors' is measured from the after-frost outdoor sowing date, which places the indoor window at 21 to 14 days before last frost. Anchored to the median last spring freeze (May 10). University of Illinois Extension · NC State Extension · University of Georgia Cooperative Extension · North Carolina Cooperative Extension, Pender County Center
Transplant outdoors
May 10 – May 24NC Cooperative Extension (Pender County) names sunflowers among the large-seeded plants to transplant outdoors after the threat of frost, giving a two-week set-out window from the last-frost date. Anchored to the median last spring freeze (May 10). NC State Extension
Direct-sow outdoors
May 10 – May 24Illinois Extension and the NC State Extension Gardener Plant Toolbox both direct-seed sunflowers after the last spring frost, giving a two-week window from the last-frost date; UGA's 'several weeks after the last frost' is later but not a number, so it could not be encoded and only argues for a later start within or beyond this window. Anchored to the median last spring freeze (May 10). NC State Extension
Variety assumption: Assumes annual garden and cut-flower sunflowers (Helianthus annuus); the indoor window is deliberately short because sunflowers resent root disturbance.
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)
- NC State Extension: Helianthus annuus (Common Sunflower) | North Carolina Extension Gardener Plant Toolbox (accessed 2026-07-25)"This annual is best planted by seed after the last frost in the spring, and harvested before the first frost in the fall."
- University of Illinois Extension: How to grow sunflowers at home - A great addition to any garden | Good Growing (accessed 2026-07-25)"Sunflowers are typically direct-seeded after the danger of frost has passed (early to mid-May). They can also be started indoors, typically 2-3 weeks before planting outdoors, if you want to get a head start."
- University of Georgia Cooperative Extension: Growing Sunflowers in the Home Garden (Circular 1121) (accessed 2026-07-25)"Sunflowers should be planted several weeks after the last frost."
- North Carolina Cooperative Extension, Pender County Center: Growing Flowers and Vegetables From Seed (accessed 2026-07-25)"Large seeded flowers and vegetables are the easiest to grow and include cucumbers, zucchini, squash, melons, cosmos, marigolds, nasturtium, zinnias, and sunflowers. To get a head start on the season, seeds of these varieties can be sown indoors in mid-March to transplant outdoors after the threat of frost."