How to Prune Snowball Bushes
The term “snowball bush” is an example of the confusion caused by the use of common plant names based on appearance or features. Chinese viburnum (Viburnum macrocephalum), Annabelle hydrangea (Hydrangea arborescens "Annabelle") and panicle hydrangea (H. paniculata) are all called snowball bushes. In Southern gardens, smooth-leaf hydrangea (H. macrophylla) is also called snowball. Prune these shrubs based on how they form their flowers. Annabelle and panicle hydrangeas form blooms on new wood each summer, but Chinese viburnum and smooth leaf hydrangea bloom earlier on last year’s growth.
Prune summer-blooming Annabelle and panicle hydrangeas anytime after the first hard freeze through late winter. Cut back dead or diseased branches any time they appear.
Cut branches on Annabelles back to between 4 and 10 inches tall each year. Pruning closer to the ground encourages fewer, larger flowers. Leaving longer stems results in branching, which leads to more, smaller flowers.
Prune panicle hydrangeas such as “Limelight” or “Tardiva” back to within 4 to 6 inches of the main stem.
Cut just above a growth node -- the thick nodules where buds grow -- on stems to encourage branching on panicle hydrangea or on Annabelle shrubs you wish to encourage to branch out.
Prune smooth-leaf hydrangea and Chinese viburnum after they finish blooming in summer or early fall. Do not prune either after August 1. Cut back dead or diseased branches anytime they appear.
Deadhead, or remove, flower heads after they fade. Cut shoots back, also called heading back, one-third their length to encourage branching. Make cuts on branches above growth nodes to encourage branching.
Remove older limbs in mature Chinese viburnum when flowers form predominantly on the upper part of the shrub. Cut from one to three of the oldest branches back to the ground to renew the shrub. You may cut up to one-third of the old stems from overgrown smooth-leaf hydrangeas to the ground to renew them. Renewal may affect the succeeding year’s bloom, so limit its use to overgrown plants or plants whose bloom has fallen off.
Things You Will Need
Bleach or rubbing alcohol
Mixing bowl and clean rag
H. macrophylla, H. paniculata and V. macrocephalum snowball bushes respond to complete renewal -- cutting the shrub to the ground -- but may take more than one season to resume heavy blooming. Annabelles will bloom as usual if cut to the ground during winter. Hydrangeas and viburnums will respond to heavy pruning by suckering -- sending up new branches. Cut these back when they appear if you want to limit the spread of your snowball bush. Sterilize cutting tools with a 10 percent solution of household bleach and water or isopropyl (rubbing) alcohol before cutting branches and after finishing each plant.
Identify existing snowball bush shrubs before pruning and complete pruning at the correct time. In addition to being time-critical, annual pruning needs vary: For example, viburnum requires little regular pruning, while Annabelle stays tidy but productive only with annual renewal pruning.
An avid perennial gardener and old house owner, Laura Reynolds has had careers in teaching and juvenile justice. A retired municipal judgem Reynolds holds a degree in communications from Northern Illinois University. Her six children and stepchildren served as subjects of editorials during her tenure as a local newspaper editor.