Answer: Most hydrangeas bloom on new shoots which develop on old wood so if you cut them to the ground, there won't be any old wood on which new shoots can develop. So, instead of cutting them back in the fall, wait until spring when the leaf buds just begin to swell on the stems. At that time, cut everything down to about knee-high. Then remove any dead stems (usually gray in color and near the center of the plant). New stems will emerge from the old stems you cut down to knee-high, and those new stems should produce flowers.
Q&A Library Searching Tips