Field notes: Be judicious in summer shrub pruning

I have recently had a lot of questions related to summer shrub pruning. The abundant spring rainfall encouraged vigorous growth in shrubs and many people feel they are a bit unruly-looking.

It is important to keep in mind that any pruning of shrubs in the summer is purely for aesthetic reasons. There are no health benefits to shrubs with summer pruning unless it is performed to remove diseased wood. In fact, summer pruning removes foliage which reduces photosynthetic capacity and actually stresses the shrub. Fortunately most shrubs are very resilient and will tolerate these stresses.

The key to proper pruning in the summer months is to limit the amount of foliage being removed to as little as possible to achieve the desired results. The best approach to reduce size of multi-stemmed shrub is to first remove a few of the largest canes. Removing approximately 20% by this method is appropriate for most shrubs. After this hand prune remaining canes back to buds or lateral branches to just lightly shape the shrubs.

For those that like a formal sheered look, the new growth can be sheered back to about 1/2 or 2/3 at the most. In many cases, these formally sheered shrubs benefit from some thinning during the dormant season to allow new growth from inside the shrub to develop.

I have recently seen a lot of shrubs that have been pruned back excessively by just cutting them back to uniform height. This is basically topping the shrubs, which indiscriminately cuts backs into woody stems. This approach results in cuts that are made at internodes along the stem where there is no growing point to resume growth. These stems die back to the next growing point and leave wounds that are easily invaded by disease organisms.


Improper pruning techniques are the most common factor in introducing diseases into shrubs. Unfortunately, the canker-type diseases that result are often difficult or impossible to correct.

More on Emerald Ash Borer

I am hearing an increasing number of people expressing concern with Rochester's current approach of removing city-owned ash trees prior to Emerald Ash borer infesting them. I am an advocate of this approach on city-owned trees as a proactive approach to managing Rochester's tree population dynamics and budget.

There is a financial benefit to the city because they can manage their workload and spread the expense over more years. If left until the Emerald Ash Borer arrives, removal of trees at the pace which would be required would be a daunting and expensive task. Another benefit is that this approach removes lower-value trees and trees in areas that have very high percentages of ash in the tree population.

This opens up spaces to begin planting and growing a more diverse population of replacement trees. When the Emerald Ash Borer does come through, these areas will already have young trees with a very good start to replace them. Neighborhoods will have a good mix of species and ages of trees, creating a more stable tree population for the future.

Jacob Ryg, city forester in the Park and Recreation Department, is drawing on experiences and advice from city foresters that have already had the Emerald Ash Borer devastate their ash populations. I have heard many urban foresters comment how they wish they would have had the insight to transition their tree populations before their cities were devastated.

The City of Rochester will not force removal of privately owned trees that homeowners choose to protect. Rochester will also allow homeowners to pay to treat boulevard trees unless they present a hazard for some other reason. Each community will develop its own policy and protocol for management.

For more information on both of these topics visit .

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