Zone 4b covers 52 days of last-frost dates. We measured Pierre, SD at Apr 28 and Jackson, WY at Jun 19. 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 4b
Zone 4b's last spring frost averages May 4 and first fall frost Oct 20 — about 169 frost-free days. Broccoli tolerates light frost, so you can set plants out ahead of the last-frost date and keep harvesting into the cooler fall. Starting seeds indoors 6 weeks ahead gives strong transplants ready the moment the soil warms. There's also room for a fall succession sowing around Jul 21 for a second harvest before frost.
Common questions
How long does broccoli take to grow in zone 4b?
Broccoli matures in about 80–100 days from transplanting. In zone 4b that means setting plants out around Apr 13 and first picking around Jul 2.
Will broccoli survive frost in zone 4b?
Yes — broccoli tolerates light frost. In zone 4b you can set plants out a little before the last frost (around May 4) and keep harvesting past the first fall frost (around Oct 20).
Can I plant a second crop of broccoli in zone 4b?
Yes — in zone 4b there's time for a fall sowing around Jul 21 for a second harvest before frost.
For soil, spacing, pests and companion planting, see the full broccoli growing guide →