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Correcting Winter’s Damage

To recover from cold weather and salt, your landscape needs TLC

It’s been a hard winter for plants as well as for us. Damage to landscapes reminds me of the winter of 1976-’77, when the Bay froze as far south as Norfolk. Compounding problems are the tons of salt and chemicals used on roads, sidewalks and driveways. On state highways alone, 480,000 tons of salt were spread this winter, more than double average usage over the past four years.
    Everywhere you look, you’ll see symptoms of winter injury to plants. The foliage of many ground cover plants such as liriope, pachysandra, St. John’s wort and creeping junipers is brown and brittle.  Many azaleas, Japanese hollies and camellias have dead branches, and many small flowering trees have broken branches from the weight of the snow and ice.
    Most of the ornamental plants used in landscaping are survivors. With patience and time, they will recover and resume growth come spring — providing their roots were not killed by low temperatures.
    Roots are not as cold-hardy as the aboveground stems and leaves. If the majority of the roots are growing in mulch as a result of over-mulching, it is highly possible that the roots died in killing temperatures of –4 degrees. If the majority of the roots were killed, the entire foliage of the affected plants will gradually turn brown as daily temperatures rise. The only solution is to wait and see. If half or more of the plant dies, it means replacing and avoiding future over-mulching.
    For injured ground cover, the best solution is to adjust the cutting height of your lawn mower to about three inches and mow the tops down so they won’t look so conspicuous. Most likely the roots of these ground covers have survived and the new growth will emerge form the crowns or rhizomes. Dead branches in juniper ground cover will have to be pruned away one dead branch at a time. Junipers are conifers and cannot rejuvenate unless there are live green or gray-green needles firmly attached to the stems.  If the entire plant appears dead, then the only choice is to replace it.
    Dead branches on azaleas, rhododendrons and Japanese hollies need to be pruned back to a main stem or branch that is alive. If the entire stem is dead, cut it within a few inches of the ground. If the root system is alive, these plants can regenerate from the stumps on stems smaller than one inch in diameter.  Recovery will be slow, however, and it may be best to replace the plant.
    Do not try to bolt together broken branches on trees and large shrubs. This will only result in rot problems in the future because the sapwood has already been exposed to rot-causing organisms. Bolted together, they will rot from the inside out. Broken branches should be pruned to a healthy stem with the cut made perpendicular to the broken branch. Never make a flush cut with the stem. If the bark on the stem has been damaged, use a sharp knife or chisel to smooth the bark and exposed sapwood so as to promote the growth of callus tissue. Do not paint with tree-wound dressing.
    Damaged grass and plants along sidewalks or driveways may be dead. Do not fertilize as this will only contribute to the salt problem. The best solution is dilution. Spade a one-inch layer of peat moss with a dusting of limestone into the affected layer to dilute the salt concentration to a tolerable level. During the growing season, the sodium concentration will be further reduced by leaching.

Ask Dr. Gouin your questions at DR.FRGouin@gmail.com. Please include your name and address.