Fall Tips for Prevention of Winter Injury to Woody Plants
By Joan Allen, UConn Home & Garden Education Center
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Winter injury to rhododendrons, above and below. |
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Purdue University |
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Frost crack on a red maple.
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Rhododendrons and other broad-leaved evergreens in Connecticut often suffer from winter injury and drying that cause varying degrees of browning and dieback. These symptoms show up in the spring sometime after the injury actually occurred, making diagnosis of the cause difficult. Symptoms on evergreen and deciduous woody plants can include tip and branch dieback, foliar browning, sunscalding and bark splitting. Excessive drying is a common problem on evergreens. Water evaporates from the needles or leaves on windy or warm, sunny days and cannot be replaced by the roots because the water in the soil is still frozen. On rhododendrons and mountain laurel, the most common symptoms are marginal browning and leaf rolling parallel to the midvein. On needled evergreens, symptoms include browning of the needle tips and centers, chlorotic or yellow flecking, loss of needles and branch dieback. In extreme cases, plants can be killed by winter injury.
Deciduous woody plants are also susceptible to winter injury. Frost cracks can develop in the bark, especially on thin-barked species such as crabapple, cherry, and maple. These occur because of expansion and contraction of bark and wood that results in mechanical stress, splitting of wood and slipping of the bark. Extreme cold can also injure flower and leaf buds. Buds may begin to break dormancy during a period of mild weather. When cold temperatures return, tissue damage occurs. This can result in a failure to flower or leaf out normally in the spring.
Winter injury is common in Connecticut because we have diverse weather during the season including late spring frosts, cool summers followed by warm falls and sudden temperature drops, dramatic temperature fluctuations causing freezing and thawing, lack of snow cover, periods of unusually warm or cold weather, and drying winds. Immature plant tissues or plants that are stressed by drought, insects, disease or root damage are all especially vulnerable to winter injury and desiccation.
Fall is the time to take steps to reduce your plants' susceptibility to winter injury and drying. Here is what you can do to prepare your plants:
1. If planting new trees or shrubs, select a sheltered planting location and choose plants appropriate for the site. Avoid planting broadleaved evergreens in open windy sites. Maintain healthy plants with proper fertilization and watering.
2. Do not fertilize in late summer or early fall. This can stimulate new succulent growth that may not have time to harden off before the onset of cold weather.
3. Water regularly during the fall and provide a deep watering before the ground freezes. Mulching will help retain moisture in the root zone and reduce soil temperature fluctuations.
4. Provide protection from water loss caused by drying winds. Burlap, wood-slatted snow fence, or other barriers are suitable. Another option is an antidesiccant spray for evergreens. These slow down the rate of transpiration by coating the foliage with a plastic or waxy material. They are most effective when applied two to three times: in late fall or early winter, during a mild period in January, and if possible again in late winter.
If spring arrives and your woody ornamentals show signs of injury, wait until new growth begins to assess the extent of the damage. In early spring, just remove twigs and branches that are obviously dead. Evergreens exhibiting winter injury symptoms may produce new leaves on branches with extensive foliar browning. Once new growth is underway, prune back dead twigs to within one-quarter inch above a live bud or flush with the nearest live branch. A spring application of fertilizer at half strength accompanied by adequate watering will help promote new growth and recovery from winter injury.
References:
Douglas, S. M. 2003. Winter injury on woody ornamentals. Connecticut Agricultural Experiment Station.
Douglas, S. M. 2003. Winter injury and drying of rhododendron. Connecticut Agricultural Experiment Station.
Protecting evergreens for the winter. University of New Hampshire Cooperative Extension.
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