I asked that question to a big name once....was told, as Stinky said, can be done but really not recommended. You need to get all the dirt off the roots which is hard by itself and then try to VERY GENTLY place them in new medium. There are things in the soil (bugs, germs) that once let loose in a hydro system can get out of control very quick. That was enough for me so I've never done it.