When I first encountered this concept—that a gardener could use too much compost—I immediately thought, “Is that even possible?” As an organic veggie gardener dealing with soil comprised of decomposed granite punctuated by lumps of sticky clay, too much compost seemed an impossibility. Isn’t compost the answer to all our gardening problems?
It’s true that “add compost” (or other organic matter, such as peat moss or leaf mold) is the best advice for gardeners dealing with either clay or sand. Organic matter opens up the solidly packed clay particles, allowing air and water—and therefore roots—to penetrate what would otherwise be an impervious substrate. In sand, organic matter acts as a sponge, holding on to both water and nutrients that would otherwise quickly drain away.