Minecraft wiki entry for Mushroom, associated text: When bone meal is applied to a mushroom, the mushroom has a chance to grow into a huge mushroom of the same color, provided that it is on a proper block (grass block, dirt, coarse dirt, rooted dirt or moss block at a light level of 12 or below; on podzol, mycelium or nylium at any light level) and has enough space (7x7x9).