USDA Hardiness Zones
The United States department of Agriculture has created a map of climate which has been adopted as a standard by the nursery trade. It is a simple system which divides the country into zones by typical minimum temperatures. The lower the number of zone, the colder the climate.
Plants are rated for particular zones, not by any official body, but by the nursery trade itself. Naturally, established nurseries have no interest in lying about the zone-hardiness of a plant. However, just because one nursery says a plant is hardy for a particular zone doesn’t mean the next nursery will agree. Plants rated for Zone 3 are usually well-tested.
This website is designed for people who live in Zone 3. Zone 1 is for polar bears. Zone 2 is for tundra. Zone 3 is the Red River Valley and surrounding regions. Zone 4 starts as you pass Fergus Falls going south, and includes the Twin Cities of Minneapolis and St. Paul.
You will notice on the more detailed USDA maps that there is a narrow band of Zone 4, which is warmer than most of the Red River Valley, which runs along the Red River as far north as Grand Forks, ND. The river, like any body of water, moderates temperature extremes.
People who live right near the river can frequently get by with growing trees rated for Zone 4. In our experience, plants listed as Zone 4 hardy are not consistently successful in the Red River Valley unless they are planted within a couple of hundred yards of the Red River.
A plant rated hardy to Zone 3 has been proven to survive temperatures as low as -40F. Plants which are rated for Zone 3 have usually undergone testing by somebody. Nurseries, both wholesale and retail, are pretty careful about how they rate trees for colder zones. If a nursery or mega-discount store cannot tell you the zone rating for a particular tree or shrub, proceed with caution. |
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