When I built my raised beds last year, I put a few lettuces between the tomatoes. Hoping the shade from the tomatoes would help protect it during the hot summer sun. One plant survived, but didn't do too well. It grew tall and went to seed pretty quick. I ate what I could off of it and let it be.. Come winter this year, some funny looking grass started sprouting up in the middle of the yard. It turned it wasn't grass at all, but the children of the lettuce. The wind must have blown the seed into the yard, where it took up shop under a nice cover of dead grass.
It has turned out to be quite the little lettuce patch. Providing all the lettuce we've needed since about the end of December.
While it may not look at organized as grass, I'd much rather use my water for plants I can make a meal out of, and its doing better than all the lettuce I planted in the raised beds. Sometimes it pays to just let the plants do their own thing.