I have never put soil on them but I mist them with a pump sprayer when they get dry. Just another school of thought, which is why gardening is so great. Kevin will tell you for sure what to do Marilyn, he is the master seedman. Make sure to tape the lid on that little greenhouse so it will not blow away but, not so much you can remove it to water. I also water the little ones with a weak chamomile tea (1 tea bag to about a gallon of water) to stop any dampening off fungus or sprinkle a small amount of cinnamon over the soil. Don't save the tea water because it gets moldy. Believe me it does.
I love those milk jugs but we don't drink anything that comes in those. Any one coming to the clinic like to save me some? I checked with Starbucks but they will not save for me.