I disagree, Senoufou, and beware of my scientific credentials on this one. I routinely sweeten my compost heap with wood ash (not too much and never ash from coal). It's by far the best place for wood ash, which washes away and acts far too quickly when directly applied to crops. Great source of potash. I'm guessing that the potash and, especially, the phosphorus in human ash would be just as good. Mine would be especially useful as they would also be a very good source of iron, which I ensure is never deficient in my diet. Could be the vin rouge...