Experts and BHG readers answer.
Why won't my established "Cityline" variety of hydranges bloom?
Cityline hydrangeas bloom on old wood. If they are pruned late in the season or if winter cold kills their flower buds, they won't bloom the following year. Flower buds are less hardy than vegetative buds, so growth may look normal following a cold winter, but the plant may not bloom. Reblooming types of hydrangeas, such as Endless Summer and Forever and Ever avoid this problem because they bloom on new and old wood, so they can form flower buds on their new growth even if winter kills the first flush of flower buds.