Cold Climate Broadleaf Evergreens
Lack of Winter Survival Adaptions Means Limited Choices
Choosing broadleaf evergreens for cold climate landscape gardens is tricky. The further north we travel, the fewer choices exist. Most broadleaf evergreens merely survive beyond plant hardiness zone 5 (- 20° to -10°), but a few grow well in their particular areas.
There are two reasons why choice of broadleaf evergreens is limited. Broadleaf evergreens are:
- Susceptible to cold climates and most are not particularly shoot (top) or even root hardy below plant hardiness zone 5; and
- Vulnerable to cold injuries such as winter burn and winter dieback even when root hardy.
Cold Injuries and Choices of Broadleaf Evergreens
The landscape gardener can extend a broadleaf evergreen plant palette to include those that grow well in plant hardiness zones 5 and colder.
- Most important is careful site observation and choosing locations that offer protection from winter wind and afternoon sun. North and east-facing locations seem the best. Snow cover, acting like mulch, also protects shrubs.
- Available soil water is critical. Winter burn and dieback of branch foliage develop when plants dry out if soil moisture is not available. Two reasons why soil water is not available are that soil water freezes so it is not available to plants, or soil was almost dry going into winter.
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Conditions causing cold injuries to broadleaf evergreens intensify and damage worsens when:
- Sunshine and dry winds batter shrubs causing them to lose leaf moisture to evaporation; and,
- Ground moisture cannot replace water lost from the leaves.
Complementary approaches for choosing broadleaf evergreens for cold climates include:
- Studying both print and online catalogs, and plant society recommendations for cold climate broadleaf evergreen plant availability; and
- Thoughtful and informed experimentation if money is not a problem.
Cold Hardy Broadleaf Evergreens
The majority of hardy broadleaf evergreens belong to the heath (Ericaceae) plant family and secondarily to the holly (Aquifoliaceae) family. They thrive in acid soils with a minimum of fertilizer. Some do well in sandy and infertile soils. Groups of cold hardy broadleaf evergreens commonly used in landscape design include:
- low-growing, mat-forming shrubs;
- small bushy and sometimes messy-looking shrubs;
- large open-textured shrubs; and
- small to large trees.