We planted our tomatoes out last Monday. We'll, most of them. We did plant some earlier, around Mothers Day. To protect them we used Walls-of-water, which you can see in the photograph. They are plastic sleeves that you fill with water and wrap around the plant. During the day the sun heats up the water inside the sleeves. During night when the temps fall the warmth keeps the plants safe inside their cocoon. The walls also help deflect any heavy rain and hail that might fall.
After years of trying them I am convinced the best bet is simply to wait until the ground, and air is warm enough to plant. During a year like this one, with all the cold and rain for spring, the walls can hold too much humidity within, and cause fungal problems. When I took off one of the walls Monday the plant had black spots on the leaves. Hopefully that will go away now that the plant has been sent free from it's enclosure. As far as size goes, the plants are a bit bigger than the new seedlings we brought home. Other than that I am not sure the Wall-of-waters are really worth the trouble. It will be interesting to see if the new, fresh seedling tomatoes planted Monday catch up to the wall of water enclosed ones planted on Mothers Day.