By Bev Johnson

Master Gardener

Now that you know how to prune trees, it’s time to learn how to prune shrubs, especially flowering shrubs. First, you need to know if your shrub blooms on old wood or new. These shrubs bloom best on old wood. Flowering quince, witch hazel, Fothergilla, PeeGee hydrangea, tree peony, climbing roses and two viburnum, i.e. Korean spice and Doublefile. 

This bunch blooms best on one year old wood: Juneberry, chokeberry, summer sweet, forsythia, mock orange, bridal wreath spirea, Thunbergii spirea, lilac, both American and European cranberry and shrub roses.

What makes shrubs ‘shrubby’ is that new stems are always growing near or at ground level to replace old or decrepit stems. This growth habit is why shrubs are so forgiving of pruning mistakes. And it’s why flowering shrubs are best pruned by what is known as the ‘renewal method. Using this method, you can prune a shrub right to the soil level or to a vigorous side shoot originating on an old stem or by removing old stems. You also prune out some of the youngest stems or suckers. Removing the old stems keeps the shrub healthy as they are replaced by new stems. Pruning mostly at ground level with a loppers or hand saw creates a graceful fountain shape. It also keeps the shrub low, neat and flowering abundantly.  

Shrubs that do well on old wood are those that naturally build up a framework of branches and rarely send up suckers. These shrubs flower directly on old wood or from shoots that grow from old wood. A few plants in this category could be considered trees, especially if they are trained to one to three trunks. These are the easiest to prune—don’t. These plants don’t grow many new shoots but if the plant starts to look crowded cut off the twiggy growth or remove one or more of the older stems. On the few shrubs that are propagated by grafting, remove any shoot that originates below the graft. You can usually do this by just giving them a sharp yank. 

Pruning can rejuvenate an old shrub. Lightly head back some of the branches every few years or cut a major stem completely off so a sucker from lower on the bush can take its place.

Lilacs and forsythia bloom best on one-year-old stems. As a result, they need regular pruning to stimulate new growth, to prevent overcrowding, and to keep the sub to a manageable size. You shouldn’t have to get the stepladder out to cut a lilac bouquet. 

The blooming stems might arise from older stems up in the shrub or at ground level. With lilacs, the blossom grows from the upper part of the shrub. Cut some of the older stems right to the ground or remove any vigorous side shoots that grow low to the ground. Then remove some suckers at ground level to prevent overcrowding. Some shrubs get wider as they get older. Just remove the wanderers if you don’t want that shape. 

Shrubs that do best on one-year stems that start at or near ground level like willows, common ninebark, or rambling roses, need a more drastic treatment. Cut them down to the ground or to various new stems growing low on the shrub. 

Shrubs that flower on new growth are the easiest to handle. Just whack the whole thing down to the ground each winter. Wait until the coldest part of the winter has passed and new growth has started. This is the best time for the gardener too as he/she is less apt to get frozen fingers.

A warning – prune spring blooming plants immediately after blooming. If you do it too early, you are apt to remove the flowers you have waited all year to enjoy.