|Why have some of my hydrangea's not bloomed in two years. I have not cut them back?|
|Plant maturity, soil fertility and weather all contribute to a plant's ability to bloom. If some of the plants are younger than others, if they aren't getting the water and nutrients they need, or if they are subjected to a cold snap which could kill off the developing flowering buds, they may not bloom. I would prune then back next spring to encourage healthy new (and hopefully) flowering growth.
Best wishes with your hydrangeas.