Shrubs usually need pruning every few years. Depending on the type of pruning, the result may be to either thin out the growth or to make the plant more bushy. Proper pruning will also promote more flowering. The time of year for pruning depends on the flower habit of the plant. Spring flowering shrubs should be pruned just after flowering. Pruning later may result in a loss of flower buds for next year's show. Summer blooming shrubs can be pruned in early spring since they produce flowers on the growth that occurs after pruning. Spring pruning will enhance the show of summer flowering shrubs.
In some cases, shrubs become too woody and may exhibit decreased bloom. In this case, renewal pruning is practiced where 1/3 of the oldest stems are cut off low to the ground. The new growth will produce the desired blooms. The next year another 1/3 of the older stems are removed, with the remainder of the older stems removed the following year. These types of cuts tend to open up the shrub for better light penetration and air movement. If all the old stems were removed simultaneously, it would be difficult to control the vigor of the new growth. Such vigorous growth is susceptible to disease and inclement weather damage.
For some shrubs, a more branched habit is desired. A pruning cut into recent year’s growth, called heading back, will promote branching from buds near the cut. For shrubs where the canopy may be lopsided or have sparsely branched areas, heading back cuts may be the answer to promote branching and fill in the holes.
Shearing is a pruning method often used on shrubs to provide a very formal appearance. Shearing removes only the tips of branches and promotes high foliage density at the end of the branch. This can be an unhealthy situation for the plant because sunlight and air do not penetrate into the plant’s canopy. Shearing can also make plants, especially evergreens, more susceptible to spider mites and aphids. However, if shearing is practiced, make sure the top of the shrub is a little more narrow than the base of the shrub. This will allow the base of the shrub to receive some sun and reduce dieback of foliage near the base. Every few years, shear into older wood to invigorate the plant and ensure new branch formation. The shrub may temporarily lose some of its formal appearance but this will help to open the canopy and rejuvenate the plant. In all cases, be sure to collect the trimmings and dispose of or compost them. If left in the foliage, these dying branches may serve as host to diseases and insects.
