Number one, be sure your soil is loose enough. Second, lettuce likes water but doesn't like soggy soil...so don't over water and make sure your soil drains well. Be sure that you thin your lettuce to give them plenty of room. Finally, try growing a variety of lettuce to see if a certain kind does well in your garden.

Yum, fresh lettuce!

If lettuce is just not happy in your garden, try growing it in a window box with potting soil. The potting soil is so light and fluffy that lettuce seems to be very happy in it. My mother has grown her lettuce exclusively this way for years. She doesn't let the lettuce get very big, rather, she snips a whole section of baby leaves for salads each day. That section grows back soon enough. A couple of window boxes full of lettuce seeds keeps her supplied in fresh lettuce all summer long. The other plus with the window box is being able to move it to cooler areas when the summer gets hot.

I think it depends on where you grow it. I can never get lettuce or salad mixes to grow in my raised beds for some reason, but I can harvest all year round from my two large pots that are 4 feet away. I never thought about the potting soil, but that may be the reason why!

I am having the same problem. I grow in raised beds with cinder block. The holes in my blocks have potting soil the beds themselves have more of a mel's mix. One bed is full sun and one is part sun. I have lettuce in both beds and in the holes and does not seem to make a difference. Everything is growing great except for my lettuce. I planted lettuce a month ago and they are still 1/2 inch to 1 tall. I however bought some butter crunch from Lowe's and surprise they are doing well. Having the same problem with Swiss chard, I finally have one taking off in a hole on the sunniest east side.