Limelight Hydrangeas (Hydrangea paniculata) are among the more forgiving members of the hydrangea family with regard to pruning. These lush flowering shrubs bloom each year on new wood, so you can prune them almost anytime--except when they are setting flower buds in the spring and early summer--without fear of eliminating next year's blooms. Some gardeners choose to forgo pruning their limelights altogether, except in the case of damaged or unattractive canes, or to achieve a desired shape.
Cut your hydrangea canes back to about half to one third of its height if you prefer sturdier stems and smaller flowers. While this may produce slightly smaller blooms, the stems will probably be sturdy enough to support them without additional staking. Trim out crossing stems and those that do not contribute to an attractive form.
Cut hydrangea canes all the way back to the ground in the late fall or early spring if large flowers are your top priority. Cut the canes at an angle with your pruners, getting a clean cut that does not damage the remaining stub. The remaining stubs will be only a couple of inches above the ground.
Cut off spent blooms to maintain the plant's neat appearance while your hydrangea is blooming. Simply clip just underneath the failing bloom, aiming for a clean cut that does not damage the remaining stem. This is sometimes referred to as "deadheading."