Melon

Melons were introduced in Minecraft 1.8 Pre-Release, the Adventure Update.

Behavior
If destroyed, melons will drop 3-7 (average of 5) melon slices; each will heal one food point. This will also happen when a Piston of any kind pushes a melon block.

A melon slice can be crafted into a melon seed to be planted as a new stem. See also other plants.

Crafting
Melon blocks can be crafted out of 9 melon slices.

Farming
Melons will have a central stem that slowly grows until it reaches its maximum size at which point a melon will spawn on one of the adjacent Farmland blocks, given that there is air above the stem. Melon stems take around 10 to 30 minutes to fully develop. Melons will revert the farmland below them to dirt when it grows. Melon stems will only grow a single melon at a time, but melons from another stem that have grown adjacent to a fully developed stem will cause that stem to connect to it. Bonemeal will cause a melon stem to become fully-grown, but will not produce a melon immediately.

For maximum melon per block yield, the following methods can be used:

o o o o o o o o o           # # # # # # # # #            o o o o o o o o o            o o o o o o o o o o o o o o o o o o            # # # # # # # # #            o o o o o o o o o            o o o o o o o o o o o o o W o o o o     OR     x x x x W x x x x     OR     x x x x W x x x x     OR     # o # o W o # o # o o o o o o o o o           o o o o o o o o o            # # # # # # # # #            # # # # # # # # # - - - - - - - - -           # # # # # # # # #            o o o o o o o o o            o o o o o o o o o   9x8 @ 48.61%                  9x9 @ 44.44%                 9x9 @ 44.44%              9x9 @ 44.44-49.38%
 * 1) # # # # # # # #            o o o o o o o o o            # # # # # # # # #            # # # # # # # # #
 * 2) # # # # # # # #            o o o o o o o o o            # # # # # # # # #            # # # # # # # # #
 * 1) # # # x # # # #            # # # # # # # # #            o o o o o o o o o            o o o o o o o o o
 * 2) # # # # # # # #            o o o o o o o o o            # # # # # # # # #            # # # # # # # # #
 * 1) = Farmland; o = Melon Seeds; W = Water; x = Any Block; - = Unused

With all these, both farm blocks and seed blocks will be hydrated.

While the left method leaves one line of hydrated farmland unused, it has the highest efficiency if you’re planning on making multiple farms next to each other because it uses 9 blocks less space (meaning 9 blocks more space for the next farm and thus 9 extra melons per 2 farms) while only losing 1 melon in comparison to the middle and right methods.

The left method has an efficiency of 48.61% and the middle and right methods are equally efficient at 44.44% with 50% being the maximum possible efficiency (2 blocks needed to grow 1 melon). Depending on circumstance (i.e. if you plan on making only 1 farm with no adjacent other melon farms) the latter 2 setups will be more efficient.

Wheat could be grown in the spaces marked 'X' to avoid wasting potential hydrated farmland blocks. 50% efficiency could be met by eliminating the row with the water, but the melons would grow much more slowly.

Designs that use the "wasted" spaces introduce ambiguity. There would be seeds with two spaces to grow into. Such a design would sometimes be more efficient than the others, and sometimes only equally as efficient.

History
Melons were first revealed in an IGN interview with Notch.

On the Getsatisfaction.com complete ideas for the Ideas section, it has stated that Watermelons will be implemented.