You cannot place plants on OVergrown Granite/Andesite/Diorite, but plants can naturally spawn on top of it. The second a block updates all of the plants on these blocks will break and cause a massive amount of updates if the foliage is dense enough. This also applies to Schist/Dacite, though unlike the other blocks they're not overgrown and you can't bone meal them unlike the overgrown stone.