Plant Lettuce in Zone 5b

Zone 5b averages 166 frost-free days, running from a last spring frost around April 25 to a first fall frost around October 8. Lettuce needs roughly 50 days from planting out to first harvest, so it uses about 30 percent of that window. Lettuce is a hardy crop, which is what decides where in the window it belongs.

Because lettuce needs a head start, sow seed indoors around Mar 28, about 4 weeks ahead of the Zone 5b last frost. Transplants go out around Apr 11. Starting earlier than that in Zone 5b usually backfires: plants outgrow their cells and stall when they finally hit cold soil. At 50 days to harvest, a 166-day Zone 5b season has room for about 2 sowings, so stagger them rather than planting everything at once.

Yes. Sow lettuce by August 19 in Zone 5b. That is 50 days before the average first frost, which covers the 50 days to maturity plus about two weeks for the slower growth that comes with shortening days, minus the roughly 14 days lettuce keeps going once light frost arrives.

Lettuce bolts in heat. Fall sowings ripen into cooling weather instead of out of it, which is why fall lettuce is usually the better crop.