Bone Meal

Bone meal is a material derived from the bones of vanquished Skeletons and used as a dye or fertilizer.

Uses
Like all dyes, bone meal can be applied directly to sheep to color them white. This is the only direct use of bone meal as a dye since it cannot be used to change colored wool blocks back into white wool at a crafting table. It can however be combined with other dyes to produce new colors:

Unique to bone meal is its use as a fertilizer - when applied to crops or saplings one bone meal is consumed and the plant grows instantly, though there is a chance of failure and in this case, the procedure must be repeated. Crops become ready to harvest and saplings will grow into trees, provided they have enough space. This effect does not work on cacti or sugar cane. Additionally, bone meal used on saplings that do not have enough room to grow will consume the bone meal with no visible effects(Fixed with 1.3 patch). Care must be taken when growing trees as the player does not block tree growth and new leaves or wood blocks may cause suffocation if they grow into the block containing the player's head.

Trivia

 * Bone meal's fertilizing properties make it ideal for growing large quantities of trees or wheat in tight spaces very quickly. A single bone's worth of bone meal can generate enough wheat for one bread or cake.
 * Using bone meal to fertilize, harvest and replant Seeds is a fast way of creating a large number of seeds at the expense of bone meal instead of hoes. This method also produces wheat and can be used to replace traditional farming methods.