Plant Broccoli in Zone 5a

Zone 5a averages 156 frost-free days, running from a last spring frost around April 30 to a first fall frost around October 3. Broccoli needs roughly 65 days from planting out to first harvest, so it uses about 42 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 Mar 19, about 6 weeks ahead of the Zone 5a last frost. Transplants go out around Apr 16. Starting earlier than that in Zone 5a usually backfires: plants outgrow their cells and stall when they finally hit cold soil.

Yes. Sow broccoli by August 6 in Zone 5a. 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.