Shrub Pruning Simplified

Given the hundreds of species and cultivars of ornamentals used in Missouri landscapes, it is inevitable that home gardeners will have questions about how and when to prune the woody ornamental plants around their homes. One could spend a lifetime studying the subtle effects of pruning technique and timing on woody plants. However, it is possible to make some generalizations that can greatly simplify pruning decisions. In searching for a conceptual framework upon which to base some pruning generalizations, I found one that seems logical in the pruning section in the A-Z Encyclopedia of Garden Plants, published by the American Horticulture Society. The table on the next page is an attempt to distill the AHS framework down to a single-paged chart that covers some of the most common landscape plants in Missouri. My incentive for developing the chart is self-interest. For some reason, I spend a lot of time every fall responding to calls and emails in which people want precise pruning dates and methods for long lists of plants. Hopefully, the chart will help home gardeners sort their plants into logical pruning groups that can be pruned at about the same time using similar methods.

A few words of explanation may facilitate the use of the chart. First, the plant groupings are based mostly on whether plants within a group form flower buds on the previous season’s or current season’s wood. For the most part, this can be determined by examining the tips of branches in fall and winter. Flower buds are usually larger and more rounded than vegetative buds. So, if a plant has many large, plump buds at shoot tips in fall and winter, these are most likely the buds that will bloom the following spring. In general, plants that bloom before June 1 do so on the previous year’s wood. If a plant has spent flowers that persist through the winter, or if it has small, pointed, inconspicuous buds in late summer, it is probably a plant that forms its flower buds on new growth in spring or early summer. However, with some spring blooming plants, like Forsythia and Vanhoutte spiraea, that produce many, small, lateral flower buds on long shoots, the difference between vegetative and flower buds may not be obvious.

Another possible source of confusion in the chart is bloom time. Terms like spring, mid-spring, early summer and mid- to late summer are used to describe time of bloom. I suggest considering peak bloom of Weigela as the indicator of early summer and first bloom of Hydrangea paniculata as the indicator of mid-summer. Some plants, such as ‘Anthony Waterer’ spiraea, confuse the issue by blooming over an extended period of time and some, such as H. macrophylla, by blooming in mid- to late summer even though the flower buds were formed the previous fall.

Lest the chart on the next page be taken too seriously, it should be emphasized that pruning is a lot like cutting hair. The more one practices, the better one gets. While there is no way to learn other than by practicing, and results of practice are not always pretty, mistakes are rarely fatal.

Chris Starbuck, Woody Ornamental Horticulture, UMC (573) 882-9630

Adapted from American Horticulture Society A-Z Encyclopedia of Garden Plants, DK Publishing