Plant Hardiness and Its Significance to Your Trees This Winter

Winter is officially nearly here. To tolerate the colder temperatures, you’re bundled up or snuggled beneath a blanket within the comfort of your home. But how do your trees face the next few months of whichever wintry mix Mother Nature directs their way?

Although freezing temperatures, snow and sleet have greeted some of us already, before the winter season ends, there’s plenty of time for more of it to arrive in our neighborhoods, driveways and landscapes. The capability of your trees to withstand such conditions may help you determine the best ways to address their care this season. Read below for an explanation of plant hardiness:

What exactly does plant hardiness mean?

When trees sense a decrease in day length and temperature as winter approaches, they begin to go dormant. This is a process in which cells in the bark begin to harden. This insulates the tree, preventing it from freezing. The more hardening that occurs in a tree’s bark cells, the more cold-hardy it is.

What is the USDA Plant Hardiness Zone Map?

The USDA Plant Hardiness Zone Map is a guide gardeners, growers and planters use to determine how likely any particular species is to cope in different regions within the U.S. Each species is assigned a number or numbers that pertain to the zone(s) in which it may thrive.

Why is the USDA Plant Hardiness Zone Map important to plant survival?

“Plant material native to the south will not react appropriately or timely to the winter conditions in the north,” says Jim Zwack, Davey’s director of technical services. For example, freezing temperatures in the north could easily harm non-native plants. Seek native plants from local, well-established nurseries when choosing specimens to bring home and plant in your landscape. “Tree problems occur when a specimen hasn’t yet adapted or cannot adapt to the environment in which it is planted,” adds Rex Bastian, one of Davey’s technical advisors.

What are some differences between cold-hardy and non-hardy trees?

The main difference between trees native to the colder, northern regions (cold-hardy) and trees native to the south (non-hardy) is the thickness of bark. Northern trees have thicker bark, and they typically grow slower and shorter than trees growing in milder climate areas, according to Aaron Carpenter, Davey technical advisor.

What about coniferous trees? Why do they stay green all winter long?

Evergreen trees have narrow needles that help conserve water and energy during winter. This allows conifers to maintain the green pigment chlorophyll in their needles throughout the year, unlike deciduous trees that break down chlorophyll and mobilize those resources during the fall color period.  A combination of frozen soils with mild air temperatures, however, can lead to the browning or “burning” of evergreens.

If you need help choosing the best trees and shrubs for your landscape, contact your local Davey professionally trained arborist for a free consultation.