Why won't my dark oak saplings grow when placed in a 2x2 square?

I have Dark Oak Saplings placed in a 2 x 2 square and with 6 blocks of space around them on all sides. Yet, they still won't grow even after I dumped four full stacks of Bone Meal on them. Can anyone provide any advice on how to grow them properly?

Solution 1:

First off, nothing neighboring the saplings - no tall grass, no flowers, no torches, no snow layers. The entire 4x4 area must be clear. Then enough room for the tree to grow, plus 1 block of margin. Some light - torches 2 blocks away suffice in case there's no daylight.

Leaving tall grass or snow is the most common error when growing 4x4 trees.