My rules of thumb for pruning hardy shrubs:
- Remove damaged or dead branches when you notice them at any time during the year. Use a sharp, clean saw to cut back to a vigorous side branch or right to the base. Clippers or loppers don't do as good a job on dead wood.
- Pinch off ends of branches that are growing too long.
- Remove suckers as they appear. Suckers are very strong, fast-developing shoots which grow straight up from roots or branches. Their stems are usually bigger but not as strong as ordinary branches. If suckers have different foliage, they are growing from below the graft. Follow them back to the main stem and remove them carefully.
- Remove flowers as they fade so seed production is halted. Otherwise the total number of flowers produced will be significantly reduced. This is especially true for Lilac and Viburnum.
- Beginning in the second season of growth, weak or spindly growth should be cut back by 2/3 in order to strengthen your shrub's performance.
- Remove any dead or damaged branches missed during regular maintenance. Check for crossing branches. If the bark is rubbed through were two branches meet, cut back the weaker or inward-growing branch to a side branch or base.
There are also some crucial differences in pruning requirements between spring-flowering and summer-flowering shrubs.
| Spring-flowering Shrubs |
Spring-flowering shrubs bloom on wood that matured during the previous growing season. By the end of summer shrubs like Viburnum and Magnolia have actually developed tiny leaf and flower buds that will lie dormant over the winter, ready to burst into bloom once spring arrives. If those branches are pruned in the fall you eliminate the flower they will bear. Therefore, spring-flowering shrubs should always be pruned immediately after they have flowered, giving your shrub the entire summer to develop flower buds for the next season.
Follow the general pruning rules above, but also prune to remove older branches. Renew main branches by cutting off old, shaggy branches which don't produce the best foliage or flowers. Cut the old branches right to the ground to avoid overcrowding at the base.
Younger branches which have born flowers should be cut back to a bud, or to new green growth that has started during the current year. As you trim, open the center of the shrub to light and air by varying the length of branches, cutting some by 1/3 or less, other by 1/2 or more. This encourages the plant to grow flowers on the inner branches.
| Summer-flowering shrubs |
Summer-flowering shrubs generally start off the spring in slow motion. They are among the last plants in the garden to recover from winter. Many novice gardeners have dug up their Hydrangeas and Rose of Sharon convinced they were dead when no foliage had appeared by mid-May. But summer-flowering shrubs remain dormant through early spring and should be pruned at this time. These shrubs bloom on growth from the current year, and need to be pruned before new growth begins.
Follow general pruning rules above but also prune back new growth once every spring. The best blooms will come from buds on branches that started during the previous season. Newer growth is tender, with lighter, shinier bark. Prune this wood back to leave two or three buds per branch.
By pruning back a portion of young growth every year you achieve a foundation of older branches with newer growth at their tips. The shrub will keep its shape from year to year and require minimal mid-season pruning.
New branches that emerge from the roots can be pruned to the base or left during the first season in which they appear. Prune them back to the same height as the rest of the foundation of growth during spri
