Allen Wilson is a Vancouver gardening specialist. Email Allen Wilson at allenw98663@yahoo.com.
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I would like to prune my shrubs so that they keep their natural shape instead of becoming hedges like some of my neighbors’. Could you give me some pointers or tell me where I can get some reliable information?
I have taught many gardeners how to prune so shrubs keep their natural shape and thickness. I have found that understanding one key principle of plant growth response to pruning gives almost anyone the understanding to do a reasonably good job.
Almost all shrubs are governed to one degree or another by a process called apical dominance. Plants have a series of buds along their stems or branches. Each of these buds has a potential to grow and become a new branch. However, the apical bud or tip bud is dominant because it produces a substance called auxin, which it sends down the stem. This auxin tells the other buds to remain dormant. If the tip bud is removed by pruning, the auxin is no longer produced and lower buds begin to grow. If only a small piece of the stem is removed, leaving several buds below the cut, three or more buds will develop into branches. If only one or two buds remain or if the cut is made just above a side branch, only one bud grows. If the entire branch is removed down to where it was attached to a larger branch, less than one branch will be produced by the plant for every one removed. Understanding the plant’s response to the three different types of pruning cuts gives you the ability to prune any shrub.
When power clippers or shears are used to prune a shrub, most of the branches are pruned just above a bud, resulting in multiple shoots or branches. After pruning twice with power clippers, the regrowth is nine times as many branches. After pruning three times, 27 times as many branches result. Many small branches growing close together result in a thick hedge-like appearance.
To summarize:
- Pruning just above a bud results in three or more branches for each one removed.
- Pruning just above a side branch results in one branch for each one removed.
- Removing the entire branch where it is attached to a larger branch results in less than one branch for each one pruned.
Before you begin to prune a shrub, look at it carefully and ask yourself these questions: Do I want it to grow more thick or dense because it is thin? Do I want it to be about the same thickness? Or do I want it to be thinner or less dense? Then choose the type of cut that will get the results you want.