Don Kinzler, Published April 26 2013
Growing Together: Choose trees, shrubs that fit region’s hardiness rating
When a tree, shrub or perennial is adapted to our climate, we call it “hardy.” Given other favorable conditions, it will survive our winters.
To assist 80 million gardeners, the U.S. Department of Agriculture produces the Hardiness Zone Map. The map was updated last year for the first time in 22 years.
The map contains 13 zones with Zone 1 being the coldest and Zone 13 the warmest. Each zone is further subdivided into A and B.
For most of my horticultural life, North Dakota and the corresponding region of Minnesota was considered Zone 3. The new map has shifted everything a half zone warmer.
Most of North Dakota is now in Zone 4A with average winter minimums of -25 to -30 degrees. The northern several tiers of counties are in Zone 3B.
Hardiness zones are commonly listed on tree, shrub and perennial tags and descriptions in nursery catalogs. Plants listed as Zones 4A, 3, 2, and 1 would be winter hardy in most of our region.
But I’ve noticed a problem. Many labels simply list Zone 4 without dividing into A or B. Our region is Zone 4A. Zone 4B is further south.
For additional insight I visited with Todd West, North Dakota State University associate professor of woody plant improvement, who advises Zone 4 material with caution, since plants labeled Zone 4 may be borderline in hardiness for some of us.
West emphasized the importance of microclimate, a portion of the larger climate, such as found in a home yard that is modified favorably by sunlight, shade, moisture, wind protection, and/or proximity to structures and established plantings.
A plant that may perform well in the microclimate of a sheltered, established yard in Fargo or Bismarck might not survive on an exposed, windswept hillside surrounding my native Lisbon. Even within the same city, borderline plants are more likely to “over-winter” in older, more sheltered neighborhoods than in new housing developments with few trees and little protection to buffer wind and elements.
Homeowners in new developments should consider choosing trees, shrubs and perennials hardy in Zones 3, 2 and 1.
Get them well-established and you will begin creating your own microclimate that will eventually allow you to diversify into Zone 4 plants.
During the years Mary and I operated our nursery/greenhouse business, one of the programs we appreciated most was the North Dakota Department of Agriculture Nursery Program, which provides for the inspection of nursery stock to ensure freedom from insects and disease.
But perhaps most importantly, the program maintains a non-hardy plant list.
State law requires nursery stock being sold must be labeled “Non-Hardy in North Dakota” if on this list.
I visited with state nursery inspector Charles Elhard, who monitors the program with the Department of Agriculture. Charles noted that through inspection and dealer education fewer non-hardy items are being offered for sale. He does occasionally find products that require the addition of the non-hardy tag.
Elhard said some of the most common non-hardy plants being sold include dwarf Alberta spruce, emerald arborvitae, eastern redbud, flowering dogwood, privet, holly and certain varieties of pears, apples, cherries and peaches.
We are fortunate to have yet another great advocate of tree and shrub hardiness.
NDSU Horticulture has an exceptionally prolific research program developing adapted tree and shrub varieties.
Can you imagine growing magnolias in North Dakota? Well, West at NDSU horticulture is actually working on it!
In the meantime I’ve decided to give my trees, shrubs and perennials a treat for being so good all winter long.
When the weather warms, I plan to apply a nice helping of well-balanced fertilizer for each.
This column was written exclusively for The Forum.
Don Kinzler writes a weekly yard and gardening column in SheSays. Readers can reach him at firstname.lastname@example.org.