University of Maryland Extension

Winter Damage - Trees and Shrubs

boxwood buried in snow
Boxwood buried in snow

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Winter Damage on Landscape Plants

Injury that occurs during the winter or early spring can result from exposure to drying winter winds, low temperatures, late frost or freezes.  The most frequently seen symptoms include:

Leaf Scorch: Symptoms of this type of damage is most severe on shallowly rooted evergreens such as azaleas, rhododendrons, holly, euonymus, cherry laurel, liriope, grape holly, boxwood, and mountain laurel.  Even newly planted white pine and spruce can suffer needle scorch during their first season from limited root systems.  In addition, needled evergreens can suffer needle scorch in exposed conditions such as along roadsides and parking lots.

Other plants prone to leaf scorch and winter injury include those at their northern limit for winter hardiness.  These include southern magnolia, crape myrtle, aucuba, nandina, hardy gardenia, and camellia.  Injury can occur on dry, windy, warm or sunny winter days when the ground is frozen.  Plants are unable to move water from the frozen soil to replace the water being lost from the exposed leaves.  Leaves curl and droop, then brown from the tips and margins, giving them a scorched appearance.  Some plants, especially rhododendrons, try and cope by rolling their leaves to minimize leaf surface exposure. Most damage is during the winter but in some cases, symptoms can occur during the spring as new growth appears after winter dormancy. 

winter scorch on hardy gardenia

Hardy Gardenia with winter scorch

Salt Injury: Heavy accumulations of deicing salts from surface applications or airborne spray, especially along roadsides or sidewalks can cause leaf and needle scorch and may kill buds and branch terminals.  This damage is caused by desiccation of the more tender tissue in buds and new growth.  Salt may also accumulate in the soil and cause root death from desiccation of root tissue.  It’s important to remember that deicing salt runoff from one sidewalk or parking lot may not cause problems, but the combined effect from numerous such events raise the harmful concentrations of salt in adjacent soil and bodies of water.

Blighting or Browning of New Growth:  Warm temperatures in protected areas in February and March may stimulate buds, flowers, or shoots into growth too early.  Subsequent cold weather and frosts will kill young buds and tender new growth resulting in fewer flowers and later leaf development.  Frozen tissue damage frequently appears as blackened buds and leaves that may also drop off.  Pruning out remaining bare branches will help stimulate new growth later in the spring.

Blasted or Damaged Blooms: This damage results when flower buds swell and then freeze during cold snaps or late frosts.  Star magnolia and lilac flowers frequently suffer from this type of injury.

Branch Dieback and Leaf Yellowing:  These symptoms occur from sunscald, frost cracks, root damage and cold weather following a warm spell.  Frost cracks can occur during the winter on exposed bark, usually on the south side of a trunk, where warming and subsequent rapid cooling causes expansion and contraction of tissues resulting in cracks.  These cracks can lead to damage of the vascular system and eventually disease cankers because of stress. 

Ice and Snow Damage: Symptoms include bent or broken branches from the heavy weight of the ice or snow.  Heavy snow can be gently knocked from branches, but ice covered branches may actually be more brittle and suffer further damage if removal is attempted.  Wind during ice storms will cause the most damage. White pines in our area are especially prone to winter ice and wind damage.

Winter Color of Evergreens: Symptoms of “winter color” can include gray, yellow, blue, purple, bluish green, brown, and bronze.  Examples in our area often include Cryptomeria – bronze, yew – brown, Juniperus virginiana – brown, arborvitae – brown, low growing junipers such as J. horizontalis– purple, and white pines – yellow.  Some evergreens such as Leyland cypress and spruce usually don’t change color. Causal factors for ‘winter color’ can include low temperatures and drought stress.  The foliage colors will revert back to normal when spring time temperatures return to normal.

Management Strategies:

magnolia with scorched leaves

Magnolia with winter scorch

Cultural practices that conserve soil moisture, prevent root damage, and promote “hardening off” prior to winter temperatures will help to reduce winter damage.  Avoid later summer fertilization as this stimulates late-season growth that does not have time to “harden off” properly and is more prone to winter injury.  When watering, soak the soil several inches deep and then allow it dry between waterings.  Freshwater sprays on foliage and deep watering in the spring will also help wash deicing salts from the leaves or needles and flush salts through the root zone faster to help reduce desiccation damage.  Deep watering will also encourage deeper rooting during the growing season which will help reduce damage from moderately dry periods and frozen soil. 

 

 

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