Shrub Pruning - June 25, 2009
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Pruning is an art and a science. The science is easy; one simply needs to take the time to study it. The art comes with experimentation, observation, and experience. Some plants do really well without pruning. Others need an occasional pruning "tune-up" to remove crossing branches and dead/diseased wood. Make sure you have sharp, clean pruning tools and study up before hand to help ensure success.
Most pruning problems begin when the wrong plant species is planted in a space that is too small. You may see this with red tip Photinia and Texas ranger. These plants grow fairly fast and can get big. Being human, we try to control the growth by shearing them down to the perfect 3-foot shrub. The first shearing causes branching to double or triple as the lateral buds begin growing in response. The next shearing simply compounds the problem by causing more lateral buds to break. Pretty soon, you have a bunch of little broom-shaped branch tips and unhealthy plants with bare patches in the canopy.
To revitalize a sheared shrub, look inside the plant and remove the broom-shaped growth and dead branches. Follow the bad branch to the point where it is attached to a larger branch and remove it. Do this with hand pruners, loppers, or even a saw if necessary. Be careful not to flush cut. Always leave the branch collar (swollen area near where the branch attaches) intact, as this tissue will regrow and cover the wound. Try to remove the old, weak stems. Continue until you have corrected the problem but never remove more than 1/4 to 1/3 of the total live canopy during one growing season. Finally, if the plant is too large for the space, remove it and plant something that grows slower and/or stays smaller.
Another common mistake is winter pruning spring blooming plants like lilac, Spirea, Pyracantha, Forsythia, redbud, and Wisteria. Winter pruning simply removes the flower buds causing the spring bloom to be lost. These should be pruned lightly, if at all, and then only after flowering has ceased. Summer flowering shrubs, such as chaste tree, crepe myrtle, Nandina, Abelia, and Rose of Sharon should be pruned in spring before growth begins. Like trees, shrubs should never be topped. This causes weak branching, lots of water sprouts, and leaves behind dead stubs.
Older shrubs can be maintained by completely removing the oldest wood at ground level and leaving younger, healthier wood. This technique is especially well-suited to deciduous shrubs such as Forsythia, Spirea, and Nandina. This approach also works well with native shrubs such as mountain mahogany and silktassel. However, some plants such as oleander and butterfly bush can be completely cut back to the ground every 5 to 7 years.
Here are some parting thoughts on shrub pruning:
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: June 17, 2009
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