Could possibly be Snow biome Affects, It decreases the speed for Oak and birch trees to grow, I always add water next to my trees somehow, It just makes me feel that it grows faster in my mind. But If your that Impatient, Just add bonemeal Edit: Im supposing it also needs a loaded chunk, Somebody has to be there at the chunk, or area
oh and I looked up trees and it didn't say anything about water. so it's not necessary to put water near trees