Minecraft wiki entry for Mushroom_farming, associated text: Farming mushrooms in this way can be rather difficult due to their slow growth. The most efficient method if one must use small mushrooms would be to plant unlike mushrooms in pairs, each pair no less than 9 blocks away from its neighbors -- preferably on mycelium so they can spread in any light level. By planting unlike pairs, one can get 10 mushrooms in a 9x10x3 space instead of just 5 in a 9x9x3 space. Obtaining a high yield requires a significant time and space investment, and typically isn't preferable unless huge mushrooms aren't feasible.