Timing is Key.
Keeping flowering shrubs healthy, vigorous and blooming profusely can be tricky but it is manageable. The most important consideration to determine is whether your shrub blooms on old or new growth.
Shrubs like Forsythia, Weigelia, Spirea, Lilac, Hydrangea and others bloom on the growth from last summer. If you pruned these varieties, and others like them, after mid-July last year, you removed the flower buds for this spring’s show. If you prune them now, you will do the same thing. So if your flowering shrubs do not flower this spring, determine if any pruning was done late in the summer or in the fall. Also realize weather-related incidents such as below freezing temperatures after buds have started blooming can kill flower buds on some plants.
The proper time to prune flowering shrubs like those mentioned above is right after they flower. One of the best ways to do this, especially on older plants, is to prune so that the entire plant is “rejuvenated”. Do this by removing one-third of the oldest (largest) canes or stems all the way back to the ground. When this is done, the plant responds by sending up new canes. In effect, we create a “new” shrub every three years. After we remove these older canes we need to take a look at the overall size of the shrub to see if it is necessary to reduce the size of the plant. Most of the time it is better to keep the natural form of the plant, but there are situations in some gardens where a more formal shape is desirable. Random removal of a portion of the longer canes will keep the “natural” look of the plant while reducing the height and width. More symmetrical shapes, like ovals or straight lines, can be achieved by trimming with hedge shears for an appearance of a manicured hedge.
However the pruning is accomplished, be sure to use shears that are sharp so the branches are cut clean and there are no ragged ends of the pruned stems left on the plant. Prune close to the remaining stem on the plant so there are no stubs where decay can begin.
Flowering shrubs that bloom on current season’s growth like Butterfly Bush and hardy Hibiscus can be pruned after they finish blooming until late March. Shrubs, like junipers and yews which do not flower, can be pruned in the winter but March seems to be a better time, after the ravages of winter weather are over.
For more information go to http://pubs.ext.vt.edu/430/430-462/430-462_pdf.pdf and look at Virginia Techs publication 430-462, Shrub Pruning Calendar. This is an easy to use chart once you have identified your shrubs.
MVG – Keeping Customers Blooming Since 1984