Last spring frostMay 6
Direct sowMay 6
First harvestJul 5
Last harvestAug 2
First fall frostOct 22
Why these dates work in zone 3b
Zone 3b's last spring frost averages May 6 and first fall frost Oct 22 — about 169 frost-free days. Sunflower is frost-sensitive, so the around last frost timing builds in a safety margin against a late cold snap — setting plants out too early risks losing them to frost.
Common questions
How long does sunflower take to grow in zone 3b?
Sunflower matures in about 60–100 days from sowing. In zone 3b that means sowing around May 6 and first picking around Jul 5.
Will sunflower survive frost in zone 3b?
No — sunflower is frost-sensitive. In zone 3b, wait until after the last frost (around May 6) to plant, and harvest before the first fall frost (around Oct 22).
For soil, spacing, pests and companion planting, see the full sunflower growing guide →