A Brief Guide to Pruning Evergreen Shrubs
Many people turn to their garden evergreens to "deck the halls" with holiday cheer. But how can you tell when a few simple snips are suddenly too much for your tree or shrub? Below is a brief guide for gardeners who are looking to gain a few extra "boughs of holly" and follow proper pruning techniques, too.
Broadleaf Evergreens
Although it will take several years to regain its original beauty, you can severely prune holly or boxwood so that only bare branches remain, should it overgrow its location. Wait to prune flowering evergreens, such as rhododendron, right after they bloom, to ensure you haven't pruned the blooms.
English Boxwood
Without periodic thinning, the thick growth of this common evergreen shrub can often be plagued with disease, as the airflow is limited and restricted amongst the dense canopy. Fortunately, only one thinning per year is needed to alleviate that potential problem, and now - early winter - is the perfect time to prune boxwood. You can thin boxwood by simply pinching off branches with your fingers (known as 'plucking'); however, pruning with garden snipers is ideal as it creates a clean break that often heals better than the rough edges created by plucking. Prune approximately six-inches deep, until the interior branches just begin to appear. Repeat until about ten percent of the shrub has been removed. Once finished, the shrub should have periodic "pockets" where stems once were, allowing air and light into the deeper crevasses of the plant. Thinning should not change the overall size or shape of the shrub, but instead will ensure stronger stems and a healthier overall plant.
Holly
Even though holly tolerates shearing, a healthier method is to follow the technique explained above for English boxwood. For Japanese holly, you can also cut each branch back between six and twelve inches in addition to periodic thinning.
Needleleaf Evergreens
The ideal time to prune needleleaf evergreens is in the early spring, however these plants can often tolerate a light shearing before the holidays, if needed.
Junipers & Arborvitae
Unlike broadleaf evergreens, junipers and arborvitae possess "dead zones" of leafless wood where no new growth will form, and delicate care is needed when pruning these evergreens. Avoid shearing with hedge clippers whenever possible. To ensure renewed growth, always allow some "foliage to remain below each cut." Because of this dead zone, overgrown plants are almost impossible to trim down to the desired size and are best replaced.
Additional Pruning Tips:
- Prune all dead, dying, and diseased limbs.
- If pruning diseased areas, always disinfect your tool with Lysol, Listerine, or rubbing alcohol between cuts to limit the spread of disease.
- When pruning limbs larger than one-inch in diameter (primarily for trees), eliminate with the three-cut approach for the cleanest cut:
- Cut halfway through the limb from the bottom up, approximately 12-inches from the trunk
- Starting from the top down, cut all the way through the stem, about one-inch past the first cut
- Make the final cut just outside the branch collar, closest to the trunk.
For information on specific evergreen trees, including average size, shape, and growth rate, "Evergreen Trees," by R.A. Cox and J.E. Klett at Colorado State University Cooperative Extension is a great publication that lists more than 50 different selections. More information is listed in the Resources section of this newsletter.
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About the Author
Courtney Capstack is a trained horticulturist from Virginia Tech. Courtney has worked at the Chicago Botanic Garden and as a volunteer
at the Hahn Horticulture Garden. Courtney currently works at the American Horticultural Society
in Alexandria, Virginia.
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Sources
Cox, R.A. and J.E. Klett. "Evergreen Trees." Gardening Series Trees & Shrubs. Colorado State University Cooperative Extension. no. 7.403. March 2005.
French. Susan and Bonnie Lee Appleton. "A Guide to Successful Pruning, Pruning Evergreen Trees." Virginia Cooperative Extension. Publication No. 430-457. December 2002. <http://www.ext.vt.edu/pubs/nursery/430-457/430-457.html.>
Relf, Diane. "Pruning Evergreen Shrubs." Virginia Cooperative Extension. April 1997. <http://www.ext.vt.edu/departments/envirohort/factsheets2/shrubs/feb88pr2.html.>
"Thin Boxwood for Improved Plant Health." The United States National Arboretum. 7 Dec. 2006. <http://www.usna.usda.gov/Garden/faqs/BoxwoodThinning.html.> |
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