Zone 6b covers 25 days of last-frost dates. We measured Columbia, MO at Apr 7 and Santa Fe, NM at May 2. Give us your town or ZIP and we'll use ten years of daily lows recorded at your own coordinates instead of the middle of that range.
Why these dates work in zone 6b
Zone 6b's last spring frost averages Apr 19 and first fall frost Oct 29 — about 193 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 6b?
Sunflower matures in about 60–100 days from sowing. In zone 6b that means sowing around Apr 19 and first picking around Jun 18.
Will sunflower survive frost in zone 6b?
No — sunflower is frost-sensitive. In zone 6b, wait until after the last frost (around Apr 19) to plant, and harvest before the first fall frost (around Oct 29).
For soil, spacing, pests and companion planting, see the full sunflower growing guide →