That is really very "personal"...how much salad do you eat? For myself only, I grow usually 4plants of red and 4plants of green, and min. 3rows of spinach. I start lettuce from seeds, 1 of each variety every 2 weeks - so I always have some ready to pick. Often new leaves start from the stem - I only get rid of stems after no more leaves growing. I also grow 4-5 var. of basil, chives, arugula, swiss chard (new leaves used in salad), also a malabar spinach-use only young tender leaves (fast growing climber, it looks nice in the garden).

I have 4 spinach plants each in a #1 nurserey pot. They seem to be doing well but I do not think they will give me too much.

Our family can, on average, go through 6 small heads of lettuce per week. None of us are vegetarians and one will only eat lettuce under duress. I agree with rina in that if you eat plenty of salads, you'll want to keep a steady supply of seedlings, slowly switching over to varieties that will tolerate heat better than ones you might think to plant now. If you have any pest problems, you might want to account for that also. That's one of the reasons that I still grow some greens in containers; if I keep them very, very close to the house, the deer probably won't eat them.