Plant Broccoli in Zone 3b

Zone 3b averages 128 frost-free days, running from a last spring frost around May 13 to a first fall frost around September 18. Broccoli needs roughly 65 days from planting out to first harvest, so it uses about 51 percent of that window. Broccoli is a half-hardy crop, which is what decides where in the window it belongs.

Because broccoli needs a head start, sow seed indoors around Apr 1, about 6 weeks ahead of the Zone 3b last frost. Transplants go out around Apr 29. Starting earlier than that in Zone 3b usually backfires: plants outgrow their cells and stall when they finally hit cold soil.

Yes. Sow broccoli by July 22 in Zone 3b. That is 58 days before the average first frost, which covers the 65 days to maturity plus about two weeks for the slower growth that comes with shortening days, minus the roughly 21 days broccoli keeps going once light frost arrives.

Fall broccoli avoids the spring problem of heads buttoning up when temperatures spike. Start transplants indoors in midsummer rather than direct sowing into hot soil.