The effects of frigid temperatures on garden plants
With periods of extreme cold come questions about the impact such temperatures may have on plant materials in the landscape. It is a good time to review potential damage to trees and shrubs, keeping in mind that much of the damage that may occur will not become apparent until new growth begins in the spring. By then, many of us will have forgotten the frigid temperatures that have now twice invaded the Heights, especially if it’s a mild spring, and gardeners may not relate plant damage to the extreme events of this winter.
Weather conditions this past fall played a part in how plants prepared for winter. Trees and shrubs in our area received inadequate moisture in the weeks leading up to the first hard frost. Rainfall last August and September was below-normal, leaving plants much more likely to suffer cold injury.
Native plant materials in their natural habitats will better tolerate these harsh conditions, but native species planted in the urban and suburban landscapes of the Heights, where soils and environmental factors are vastly different from their normal habitats, can experience cold injury due to stress imposed by these exotic habitats. Most woody ornamental species used in Heights landscapes are non-native, and even a species rated hardy to our region may not survive when exposed to extreme temperatures. Keep this in mind when assessing plant problems in the spring.
Significant root kill will certainly affect the survivability of landscape plants. Soil by itself is a good insulator, and in most winters it provides adequate protection for roots. Snow cover is also important, as it provides natural insulation that can help to protect root systems. If low temperatures affect roots, it is the feeder roots—those closest to the surface—that are likely to be killed. The roots of plants in above-ground planters or containers, of course, are much less protected and are subject to direct injury or death from the cold.
One type of cold injury that is most predictable is the killing of flower buds on those trees and shrubs that are marginally hardy in our region. For example, the buds of forsythia, a common ornamental in Heights gardens, are prone to winter kill when temperatures drop to 15 degrees below zero.
Evergreen trees and shrubs are at additional risk as they continue to evaporate moisture due to winter’s drying winds. Frozen soil prevents replacement of this water. The beautiful mature landscapes surrounding our homes include many rhododendrons, azaleas and the like—broadleaf evergreens that are particularly susceptible to winter burn, a common injury that results in brown, yellow, or, sometimes, dead plants in the spring. A late-fall application of an anti-desiccant to these plants can significantly reduce this moisture loss, thereby giving shrubs and trees an edge against winter injury. The spray’s effects last through the winter and help to maintain the evergreens’ natural color and protect them from salt damage.
The frigid weather and the possible types of damage that it could cause should be kept in mind when evaluating plant growth or death come spring.
Lauren Lanphear is the third-generation owner of Forest City Tree Protection Company in South Euclid, founded in 1910. He is a past president of both the Tree Care Industry Association and the International Society of Arboriculture and has been a member of the Church of the Saviour since 1969.