|Figs and other fruit trees are best pruned in winter, as are crepe myrtles. When you look around the yard after a hard freeze, though, your first instinct may be to race out and cut off anything brown. Go ahead and clip the browned perennials, but think before you panic about trees and shrubs since most will rebound quickly without permanent damage. Suppress that pruning urge until you’re armed with the facts about winter damage to plants.
Listen to Doc: Dr. Frank Matta, Horticulture Professor at MSU, describes what to look for when surveying trees and shrubs for damage after hard freezes.
The symptoms of cold damage to woody plants are: leaf browning,
followed by leaf drop, or blackened portions on stems of evergreens.
In deciduous trees, symptoms are primarily branch dieback. If the
cold damage is severe, entire branches or stems will be killed.
Vertical bark splitting is a common symptom of mid-winter freezing
due to cold and is a result of sap-flow due to heat from the sun,
(followed by) a sudden drop in temperature that causes intracellular freezing.
Landscape Architect Randy Graves, co-owner of Madison Planting and Design Group, explains that not all of these symptoms appear at once, particularly bark-splitting. For example, he says, “damage to Indica azaleas will not show up for three years and will be attributed to this cold spell.” Any woody plant can be susceptible to bark split and it is always disfiguring and usually fatal. The damage occurs at the base of shrubs and presents over time when a section of the shrub fails to bloom or to leaf out.
Many leafless branches, including evergreens, may be capable of regenerating if allowed a few weeks to recover. Randy Graves advises, “Watch for dry periods in January and February…colder weather makes soils dry out quickly. Hold off until March to really prune…Pruning now will encourage new growth at the wrong time of the season.” And you might cut off what could come back if given a little time. To reassure yourself, do the scratch test. Use your thumbnail to gently scrape a bit of bark off the tip of a branch. If it’s green underneath, it’s alive. If the tip is brown, move back down the branch and test again. Even if the stems are dead, thickety shrubs like spirea can recover. Be patient for now, look for new growth in March, and prune out the dead wood then.
I know from sad experience that unprotected vegetable gardens are dead if the plants are brown to the ground. Even hardy Brussels sprouts are lost if their main stems are brown. The exception to this pronouncement is perennial vegetables such as asparagus. While the ferns are certainly browned, as are the tops of most perennial flowering plants, their roots have likely survived. The future of perennials depends in part on what you do now, especially if they have also been waterlogged. Cut down woody stems such as lantana but take special care with green stems like elephant ears. If the frozen debris detaches at your first touch, remove it, but do not pull on stems. Cut or saw down these more resistant green stems including banana plants to prevent damage to the crown and roots. Mulch up to, but not over, the crown of dormant perennials.
Randy Graves encourages gardeners with landscape plant damage to avoid repeating the experience. He reports that his clients’ plants did well because they were “mulched properly to tuck them in for the cold, fertilizers (were) applied properly with no or minimal nitrogen after June…Overfertilized plants push too much fall and winter new growth that leads to damage.” Sometimes cold damage is a combination of plant care and plant choice. As Graves says, “If you had damage or you found yourself running outside to cover plants, and if you lose these plants, think very hard when you replace them – keep it real!”