Zone 6b covers 17 days of last-frost dates. We measured Springfield, MO at Apr 6 and Detroit, MI at Apr 23. 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 Nov 6 — about 201 frost-free days. Marigold 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. Starting seeds indoors 6 weeks ahead gives strong transplants ready the moment the soil warms.
Common questions
How long does marigold take to grow in zone 6b?
Marigold matures in about 45–55 days from sowing. In zone 6b that means sowing around Apr 19 and first picking around Jun 3.
Will marigold survive frost in zone 6b?
No — marigold 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 Nov 6).
For soil, spacing, pests and companion planting, see the full marigold growing guide →