Herbaceous shrubs such as hydrangea, butterfly bush and Russian sage, can be severely pruned back annually at the end of the growing season. If the shrubs become too leggy during the growing season, gardeners can perform light trim in addition to the end-of-the-year pruning job. Avoid pruning back your shrubs on a hot day since this causes stress; work on an overcast day when the sunlight is weaker.
Cut back your herbaceous shrub at the end of the growing season, using anvil pruners or hedge clippers. Chop your shrub down to the ground, leaving no more than 6 inches of growth remaining. During the next year your herbaceous shrub will regenerate new growth. This is an end-of-year pruning task. For periodic trimming, skip this step.
Check the branches of your herbaceous shrub for signs of dead, damaged or diseased growth. Dead branches will feel hollow, while diseased and damaged ones sport discolorations, markings or wounds. This can be done any time of year as part of a trimming program, according to University of Missouri Extension.
Spritz anvil pruning shears with a disinfectant spray. Clip off dead, diseased or damaged shoots at their base with the pruners. In between each cut, spray the pruning tools with the disinfectant spray. This prevents you from spreading bacteria or fungus to healthy parts of the shrub.
Trim the overall shape of your herbaceous shrub using hedge clippers. Determine how tall you want your shrub to be, then cut back the top growth until your shrub is 1 to 2 inches shorter than your desired height. This can be done during the growing season as a trim job to keep herbaceous shrubs from getting bushy.
Pinch off spent flowers during the growing season, using the tips of your fingers to nip them off. This encourages new growth and should be done throughout the growing season as flowers die.
Cut off any low-growing or downward-growing stems that could be trampled and broken by critters. This can be done any time as part of a trimming program.