Looks everytime like this with closed corners/edges.
Wiki says: (13w05) <<< Rebalanced bonemeal
Everything now usually takes 2-3 uses to fully grow, but it's random>>>
In my own Tests it was "usually around 6" as i mentioned and not around 2 or 3. In obstructed places it often takes a whole stack or more!
Looks everytime like this with closed corners/edges.