Comfrey (Symphytum) is a wild and robust perennial plant, occurring naturally throughout Europe. Rich in nitrogen, potash and boron, it helps to fertilize the soil and behaves like a real compost activator.
Its roots, on the other hand, have a significant concentration of pyrrolizidines, which can be toxic to the liver. Comfrey leaves can be used to make a natural liquid fertilizer, called comfrey manure. It can also be used against aphids as a natural repellent.