Cold Climate Broadleaf Evergreens
Lack of Winter Survival Adaptions Means Limited Choices
Jan 19, 2008
Overview
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.
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.
Articles about Environmental Factors at Landscaping at Suite 101
- Environmental Factors - Part 1: Recognizing and working with environmental factors helps to avoid expensive and distressing landscape design mistakes.
- Environmental Factors - Part 2: The sun's height in the sky is crucial in determining climates and microclimates. Latitude, longitude and the earth's tilt govern amounts of sun reaching locations.
- Microclimates: Many world-renowned gardens utilize both natural and manipulated microclimates to achieve drama and beauty. They utilize existing structures like old brick walls and buildings along with natural influences such as compass direction, water, and large trees.
- Sun and Shade: Knowing the daily and annual sun positions helps to make landscape designs accurate and realistic. Sizes of extremely shady or sunny spots are easy to estimate.
© Text and photographs, except where noted, by Georgene A. Bramlage. 2008. Reproduction without permission is prohibited.
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