Depends on where you are located, your climate, your soil temperatures. Lettuce won't even germinate in hot soil much less grow to bolt. Where I am there will be no more lettuce planting until mid-September.

If you have a heavily shaded area then some varieties are a bit more heat tolerant once they are established but you still have to get them to germinate first so you may have to do that indoors.

Dave.

I am in north central Indiana. I have shade that I can use, so should I plant a small area at a time? Thanks for taking the time to answer. Barb

For a number of years I sold lettuce and other mixed salad greens through the season. The key to summer lettuce is first to have summer varieties that can handle heat. I direct sowed by rigging up some shade and kept the bed moist by watering twice a day. It works, but is labor intensive.

I will be planting some Muir this weekend in advance of my main fall planting next month. Never had any issues with germination with any summer plantings here, and Muir is practically bolt proof.

I sowed some lettuce last weekend in a shady spot (under an A-frame trellis of pole beans). Everything has come up, so it seemed to have worked. As LaceyVail mentioned, shade plus lots of moisture seems to help with the summer lettuce.