I don't see why not! I've found that organic soaps work just fine (Burt's Bees, 7th Generation, etc) but some people swear by Dawn. Now, from what I've heard, Dawn is not harmful to the environment and it has actually been recommended to me by a vet for killing fleas on my Cat. There's also specific soap sprays for the garden that aren't harmful. You could find it at your local garden center.
