The time has come to attempt to determine how much damage was done to trees and shrubs by cold weather last winter. There was almost total browning of foliage on some broadleaf evergreens such as evergreen, magnolia, hybrid rhododendrons, azaleas, pleris, camellias, boxwood, ligustrum (evergreen privet) and Chinese and Japanese hollies.
Dead wood should be removed. The thumb-nail or a sharp pocket knife are the best tools for making the determination of what is dead. Scratch or cut through the bark at the tip of a stem. If it is yellow, tan, brown or black, the cambium layer of cells (located just beneath the park) is dead at that point.
Move a few inches down the stem and scratch or cut again. If there is the same evidence of death, keep on scratching or cutting at a lower point. If you reach a place on the stem where the cambium is green (and the wood beneath it is white), prune away the stem above this point.
In some cases, this may be at the ground level. If the entire top is dead, remove it and say a prayer that new shoots will come up from the roots.
If in four weeks there is no sign of new green shoots, dig out the plant and replace it.
When pruning away dead or dying wood, make the cut an inch or two below the injurred area. Use sharp pruning tools to avoid tearing the bark or causing additional injury. Wound dressings on pruning wounds have been found to be of no value and are no longer recommended.
After pruning, fertilizer lightly, using 5-10-5 or 10-6-4 fertilizer. Use about 1 pound of 10-6-4 per 1,000 square feet, or 20 pounds of 5-10-5. Any more than that may cause injury to the roots.
If the soil is dry at the time, watering is recommended. An inch of water (rainfall or watering) every 10 days is recommended throughout the spring the summer (assuming the plant is making a come-back).
Avoid overwatering plants. It will make the situation worse by creating water-logged soil which prevents air from getting to the roots.
A number of deciduous plants such as pyracantha, crepe myrtle and roses also were damaged. In all cases remove the dead wood. Among the ground covers, English Ivy appears to have been hurt the most. Remove the damaged tissue.
One of the main cuases of severe damage or death of broadleaf evergreens was desiccation. The soil containing the roots remained frozen for an extended period of time and the roots were unable to replace the moisture lost by transpiration.
High wind contributes to loss of moisture. The heat of the sun can cause stomates on the lower sides of the leaf to open, increasing transpiration.
Could the damage have been prevented? Probably yes in many cases. A three or four-inch mulch (of tree bark, for example) would have provided insulation which would have maintained a higher soil temperature and decreased the depth of freezing. In many cases, this could have made the difference between death or severe damage and relatively little damage to marginal plantings.
In some cases, two azaleas side by side, one badly damaged, the other only slightly soindicates one had a better root system, extending below the freeze-line.