Getting Ready/Lettuce Seedlings

This weekend, we will be working in the yard. I will also be cleaning up an overgrown bed in the backyard where I'm putting some of the peppers and our lettuce. I'm hardening off the lettuce seedlings above. It is Rouge De Grenobloise/Grenoble lettuce, and I can't wait to eat it in salads this spring and summer. I let the seedlings overgrow a bit, but they seem healthy - so I don't think there is much to worry about.

My tomatoes are growing in leaps and bounds, though. I've had to transplant them twice for root development, and they are doing wonderful. They smell like tomato plants, too, which is really exciting. One of my favorite smells next to basil. I'm a little worried about the "Georgia Clay" in our area, though. I think we are going to supplement it with horse manure. I did a soil test the other day and the pH was fine, but I don't want to take any chances - I really don't want to wait until August and realize my garden is as hard as concrete. Does anyone have any suggestions for dealing with clay soil?? I would appreciate them.