A few years ago I wrote about the challenge of pruning landscape plants. It is a complicated subject since one pruning style does not apply to all plants.
Each type of plant has a natural form that should be retained or enhanced. For example upright growing tall trees should not be topped. An occasional light side limb length reduction is enough to maintain their form and keep them safe.
Shorter full shaped trees can be tipped while training without hurting their natural form and health. Pruning trees for size control is typically not a good practice. Just choose the right size tree for each unique site to eliminate the need to top trees.
When preparing to prune shrubs, remember three basic forms that nearly all shrubs fit into: a mounding form, cane producing form and upright tree like form.
To retain their natural form, prune mounding shrubs very little with just an occasional thinning cut to remove branches that become too compact or tight. This would apply to shrubs such as spirea or azalea.
To maintain a cane producing shrub like lilac or viburnum, never top them but instead just cut out a few of the oldest canes or trunks at the ground level each year if the plants start getting too woody or tall.
The upright shrubs like rhododendrons or camellia should never be topped to retain their beautiful shape. On occasion it may be necessary to thin them if too compact or to do some corrective pruning to broken branches.
Choosing the right shrubs for each location in your garden will help you create a balanced and beautiful landscape. Making gum drops out of every bush for size control is not attractive, and can shorten the life of your plants.
To reduce the shock of pruning, know the best time of the year for both trees and shrubs. Most deciduous trees, including fruit trees, are usually pruned during the dormant season in winter. This reduces the shock of having a large percentage of their leaf area removed during the growing season.
There are exceptions, however, that are really important to remember. If you have a fruiting cherry, flowering cherry, peach, nectarine, or plum tree that gets bacterial blight, a disease that causes bud and branch dieback and oozing sap, it is important to do your pruning in the fall before winter rains begin. This allows the pruning wounds to callus and harden when the weather is still dry, preventing the spread of bacteria into the pruning wounds.
Pruning fruit and flowering trees annually is important to improve air and light penetration into the canopies to reduce disease, and to reduce the tendency to over produce fruit that can break limbs.
The fall and winter are good times to prune conifers since the new growth has hardened and trees are at their most dormant stage. Pruning in the fall before steady rains begin will allow wounds to callus best.
This year you may have more pruning than usual to do to correct the damage that occurred to your trees and shrubs during the snow storm in late February. Remember to follow the general rules for pruning I have already commented about, but once in a while you will have to retrain trees that have lost their leader or natural upright shape.
After removing any damaged branches, you should look to save new shoots that arose from broken limbs that have good, strong crotch angles and are positioned to maintain the tree form. Don’t allow too many new shoots to arise from the same site. You will probably have to do some shoot removal of poorly positioned shoots.
This training and thinning of branches will take several years, so be patient. If you are uncertain how to retrain your trees and shrubs you may want to register for the Master Gardener program that will begin in January 2020, or look for our pruning classes for the public that we have in January and February at our OSU Discovery Garden near River Forks Park.
We are currently accepting applications at the OSU Extension office for the Master Gardener program.