Re: Comfrey. Beware if starting it from seed, or getting it from an old planting. Comfrey is invasive. It spreads from roots, and also spreads readily from seeds. There are some new varieties which are sterile. So, you don't have to worry about it reseeding all over your property. The root systems go 10' deep, which is one of the reasons that the plant is so hardy, and provides such a nutritional boost to your compost. It mines minerals from deep in the subsoil. Any how, Bocking #4 is recommended for feed supplements, Bocking #14 is recommended for building compost. What ever you do, if you plant it, be sure you plant it where you want it to STAY! as it's difficult to get rid of, once it's planted. I've heard that the only way to get rid of it is to turn the chickens loose on it!!!