Sometimes I will plant a sapling and come back to find that it has not grown at all, while other times it will grow fully.
How many free spaces/blocks around the sampling (both width and height) do you need for a sapling in Minecraft to have a 100% grow chance?
Best Answer
From the wiki:
These are the minimum requirements. Larger gaps then the minimum appear to cause the trees to grow faster and/or need less bone meal. If these minimum requirements are met, they will grow 100% of the time. I have grown trees right next to each other.
Don't forget that saplings need a light level of 9 or higher. Growing too many trees close together can block light from getting to a sapling.
Also, oak saplings ignore the adjacent blocks and will grow anyway. They can be grown right next to walls. Do not try to stop their upward growth with dirt though, as they will grow through dirt and replace it with wood trunks.
Here is an image of oak saplings and then them grown into trees next to each other:
More extreme, here is giant spruce: