Identify Frost Damage
Winter damage can occur on many plants, some that you wouldn’t expect. A rapid temperature drop following a mid-winter thaw (which we’ve seen) can cause bark splitting. Dead twigs and branches in the spring may be the result of ice and snow damage from the winter. Injury during the winter or early spring season can be from frost or freeze injury even if the damage from cold weather sometimes doesn’t show up for several days or even weeks.
Some evergreens, like the rosemary here in the pollinator demonstration garden at the McSwain Center, display yellowing or bronzing of the needles when exposed to winter sun and wind, but return to normal color when growth resumes in the spring. Winter injury may be confused with early stages of some fungal diseases. Needles turn from bronze to reddish brown or brown, as a result of exposure to cold, dry winter winds.
Suspect cold damage when branch tips do not leaf out but lower parts of the plant do so. Although my beautiful blue hydrangea macrophylla is planted in a protected place, this winter’s bitter cold had taken its toll. Hydrangea flowers on twigs that grew last fall and like many other plants, had already pushed out new growth. The hydrangea branch tips that I was looking forward to providing a beautiful show, are now just showing cold damage. They will likely not flower this year but limbs closer to the ground that show no damage might produce flowers in later on, weather permitting.
Suspect cold damage when leaves have unusual patterns of dead cells. For shrubs and trees, the best plan is to wait a until after the last chance of freeze is past (around April 19th here, give or take 12 days) and then prune away stems that are not producing leaves. Most woody plants will produce leaves and will bloom normally in summer if they are not permanently damaged.
Permanent damage occurs when conditions are severe, prolonged, or when temperatures change suddenly. Tissue death is caused by the removal of water in the needles faster than the plant can replace it through root uptake from frozen water in the soil. Winter scorched needles eventually drop off.
Leaf scorch symptoms can occur on broadleaved evergreens too. Damage is most stark on shallow rooted plants such as azalea, rhododendron, holly, grape holly, boxwood, mountain laurel, etc.). Injury occurs on dry, windy, warm or sunny winter days when the ground is frozen. Plants are unable to move water from frozen soil to replace water lost from the leaves. Leaves curl and droop, then brown from the tips and margins, giving the leaves a scorched appearance. In many cases damage occurs during the winter months but symptoms appear in the spring as the plant begins to emerge from the winter dormant period and move into the spring growth phase.
There are steps that we can take to reduce the risk of winter injury; choose plants that are hardy in our area, place plants in partially shaded areas protected that are protected from winds, position physical barriers about 18 inches away on the windward side of young trees to reduce wind velocity. Keeping the soil moisture adequate in the fall helps to prevent desiccation. If all else fails and you find damage in the spring, prune out affected areas. If you would like more information about how to create, care for and enjoy a beautiful, bountiful and life-enriching garden this spring join us in the Garden Life education classes.
Minda Daughtry is Horticulture Agent for North Carolina Cooperative Extension in Lee County.