I placed some spruce 2x2 saplings in a plains biome, I can assure there was enough space around it to grow. Probably after an hour it still didn't grow. I could grow it with bonemeal.  

The same thing happened yesterday. Almost the same spot where this happened. Note that this time I did not let it grow with bonemeal but instead I replaced the saplings with others on the exact same spot. Those replaced saplings did grow after some time.

I have a lot of 2x2 spruce trees in the area, but all about ~15-20 blocks apart. 

These chunks were definitely loaded, it was around 2 chunks away from my house. I was playing on my Realm. I have my render distance to the max.