Many hydrangeas flower on NEW growth and the stem from the previous season can be cut back by half or even all the way to the ground. *Are the brown leaves your writing about coming from the stems of last year’s growth? If so, those leaves and stems are not necessary for *this* year’s growth* I leave some previous year stem about 12-18 inches depending the on the hydrangea size and previous years flower display, only for the purpose of acting as a support for the current years flower blooms, which can be massive. More flowers will result from early spring/winter pruning- depending on the hydrangea type. I am referring ONLY to my types which are either Limelight or Annabelle. I have no idea what type you have, but they look similar to mine.