The bug

Trees can no longer grow with blocks next to the sapling. For oak trees, only large trees can spawn if there's a block next to the sapling.

All blocks except dirt, grass blocks, logs, and other saplings are affected (see MC-15224).

To reproduce

1. Plant a sapling
2. Have any block next to it
3. Spam bone meal on it
   → The tree won't grow (or is a giant tree if an oak sapling was used)

Original description

Its impossible to grow trees with a dispenser on the next block to the sapling, preventing automation.

Even tall grass obstructs growth of the trees. Trying to grow an oak always require tonne of bonemeal and results in a large oak variety.

Growing other types, like birch, with any blocks around it would cause it to fail to grow.

Previously for a tree to grow, it required 1x1 space at the sapling, and 3x3 above, while for 2x2 trees it was 3x3 at the base and 5x5 above, and blocks like leaves, or logs won't obstruct it.

Many tree farm design followed these design principles for years.

Currently all the tree farms are broken as tree won't grow next to a dispenser, rendering that dispenser functionality useless.