Eat Your Thinnings
My summer lettuce patch is partially shaded by large squash leaves. This keeps the lettuce from bolting during the long, hot summer.
I originally broadcast my seeds rather than sowing in rows to maximize the amount of produce grown in such a small space.
Using this approach it is necessary to periodically thin out the plants to give them enough room to grow and allow for adequate sunlight and nutrients.
As you can see in the photo above I got a bagful of lettuce and one of basil by thinning out the lettuce patch. You could hardly tell that i made a dent.
Bottom-line: periodic thinning will keep you in lettuce (and basil) all summer.