I have planted Iceburg twice and neither time did it form a "ball" like I am used to seeing it in the store. I did get it planted a little later than is recommended, but my other lettuces did OK. Any suggestions before I try it again this year?

I have never been successful with iceburg, either. For some reason it is harder to grow. 2nd best is Romaine and it does much better for me.

I've had fair luck with head lettuce, although they are smaller (and sweeter!) than the grocery store variety. Unlike leaf lettuce, I keep them spaced apart much more.