There are many factors that contribute to whether or not plants such as hydrangeas bloom. For example, if the plant is in an area with too much shade, the plant will not form buds. If it's experiencing too much sun, the plant will try to conserve energy by not forming new buds and will therefore not bloom. Other factors such as cold weather, deer browsing and the age of the plant are factors that can prevent your hydrangeas from blooming. There is some action you can take to promote growth. This includes watering the plants at the root trying to avoid the leaves and flowers or buds. Pruning at the right time in the year will also impact whether or not your plant will flower. Lastly, using a slow-release fertilizer will improve the blooming rate of your plant.