Book 29, Question 122
Why do gardeners call worm castings “black gold”?
Castings are worm droppings.
They look like tiny dark crumbs. They hold nutrients in a form plants can take up easily, and they are full of helpful microbes. They are not the same as soil, and they are too rich to use alone. Gardeners mix a little into potting mix, about one part castings to four parts soil. Because castings are gentle, they rarely burn roots.