Plant Lettuce in Zone 4b

Zone 4b averages 146 frost-free days, running from a last spring frost around May 5 to a first fall frost around September 28. Lettuce needs roughly 50 days from planting out to first harvest, so it uses about 34 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 Apr 7, about 4 weeks ahead of the Zone 4b last frost. Transplants go out around Apr 21. Starting earlier than that in Zone 4b usually backfires: plants outgrow their cells and stall when they finally hit cold soil. At 50 days to harvest, a 146-day Zone 4b season has room for about 2 sowings, so stagger them rather than planting everything at once.

Yes. Sow lettuce by August 9 in Zone 4b. 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.