Close-up view of a thriving vegetable garden with various plants Growing Lettuce in Zone 6b One important note for Zone 6b: lettuce is a cool-season crop, so the trick is working with the seasons instead of trying to force it through the hottest part of summer. In Zone 6b, spring planting is generally around April through May, while a fall crop can be started roughly late July through September, depending on whether you're growing baby lettuce or full heads and on your local