When any blocks are placed in a 3x3 area around the north-western sapling of a 2x2 spruce or jungle tree, it won't grow. this includes other saplings (even of the same type), dirt, logs, leaves, podzol, mycelium, and dispensers trying to grow the tree. in older versions, it could grow without any horizontal clearance at the sapling level, and all other trees can also grow without horizontal clearance, including dark oak. it won't even advance a single growth stage. as you can see from the screenshot, the dispenser is trying to grow the sapling and the growth stage is still 0. this dispenser has been left running for quite a while.