Last spring frostMay 7
Direct sowMay 7
First harvestJul 6
Last harvestAug 3
First fall frostOct 13
Why these dates work in zone 4a
Zone 4a's last spring frost averages May 7 and first fall frost Oct 13 — about 159 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 4a?
Sunflower matures in about 60–100 days from sowing. In zone 4a that means sowing around May 7 and first picking around Jul 6.
Will sunflower survive frost in zone 4a?
No — sunflower is frost-sensitive. In zone 4a, wait until after the last frost (around May 7) to plant, and harvest before the first fall frost (around Oct 13).
For soil, spacing, pests and companion planting, see the full sunflower growing guide →