Quick Tips for Pruning Flowering Shrubs

Pruning is a source of confusion and worry to many gardeners, but it doesn't need to be. Knowing and understanding the principles behind pruning flowering shrubs can help you prune like a pro!

Rule Number 1: Pruning is not required for a shrub to survive.  
Many gardeners labor under the belief that they must prune regularly to keep their shrubs healthy. In reality, the health of a shrub isn't typically tied to its health. Even in the case of shrubs where we recommend once-yearly pruning, like panicle hydrangeas and roses, it's not imperative. Pruning simply results in a more compact plant with better blooming. Pruning common shrubs like lilacs, forsythia and burning bush into tight mounds is not only unnecessary but isn’t that great for the plants, either. Many flowering shrubs will look their best when allowed to grow in their natural form or habit. Frequent shearing encourages lots of surface branching, possibly resulting in an unhealthy structure and reduced flowering. If you really want a tightly sheared look in your garden, choose a plant that is suited to it, such as boxwood. 

Rule Number 2: Prune most spring flowering shrubs after flowering. 
Plants that bloom in early spring usually form their flower buds the year before (old wood). The buds over-winter on the previous year’s growth and open in spring. If you prune these spring bloomers in fall or winter, you’ll remove the flower buds and won’t have flowers that year. The plants will recover, but you’ll miss a year of blooms. Most of these plants don’t need heavy pruning every year, just some selective thinning of branches to give them a nice shape. 

Rule Number 3: Prune most summer flowering shrubs in late winter or early spring.
Many summer flowering shrubs bloom on the current year’s growth (new wood). Pruning them back in late winter encourages them to produce lots of new growth that summer and will result in more flowers. Don’t be afraid to cut fast growing plants, such as buddleia or caryopteris, down to as little as 10-12” tall. The exception to this rule is hydrangeas. See Rule Number Four for more on that. 

Rule Number 4: Hydrangeas have special pruning rules that you'll want to master. 
Hydrangeas alone account for at least half the pruning questions in gardening advice forums. Some types bloom on "old wood" (see Rule Number 2) while others bloom on "new wood" (Rule Number 3.) You’ll need to identify what kind of hydrangea you have and follow the appropriate rule. Hydrangea macrophylla and Hydrangea serrata, the ones with big blue or pink flowers, and Hydrangea quercifolia, oakleaf hydrangeas, all bloom on old wood. The little pruning they need should be done immediately after flowering. Hydrangea paniculata, which have white, conical flowers, and Hydrangea arborescens, such as ‘Annabelle’, bloom on new wood. They’ll produce better flowers if cut back in late fall or early spring. For more in-depth information on pruning the different types of hydrangeas, click here.

Rule Number 5: It’s OK to prune anytime if it's really needed.
Gardeners are often confronted with stray shoots and branches in late summer and worry about removing them. Branches could also break at any time during the year. Go ahead and cut those stray and broken branches back. The plant won’t be damaged by removing a branch or two.      

In summary, don't worry! Your landscape plants don’t need as much pruning as you may think. If you’d rather go to the beach than shear back your landscape plants, go right ahead. The only potentially tricky part of pruning is determining when to trim a particular plant. For a quick review, prune most summer bloomers in late winter and most spring bloomers right after flowering. An exception is hydrangeas which have their own set of pruning guidelines. Stray or broken branches can be trimmed back any time. If you do make a mistake, plants are very forgiving. You may miss a season of flowers but the plant will recover for the next year.