Last year the USDA updated our country’s Plant Hardiness Zone (PHZ) Map and portions of Minnesota have been changed from zone 4b to zone 5a.
First a quick look at how they determine the zones. PHZ are based on 30-year averages of weather extremes. For this new map, data was collected from 13,625 weather stations. A large increase from the 2012 PHZ map. Note: Many climatologists believe this new PHZ isn’t really a change but rather a more accurate measure.
Where are the new boundaries of this Zone 5a? Basically, the area from northern Dakota County to southern Anoka county through Ramsey county to the western portion of Washington. Note, these are metro areas where “heat islands” exist due to the number of buildings, roads and limited natural spaces. Southwestern Minnesota from Marshall to Austin have been labeled Zone 5a since 2012 and remain that way.
What does it mean for planning/planting purposes? Overall, not all that much. The lowest average cold temperature for Zone 4b is measured between 20 and 25 degrees below zero. For Zone 5a the lowest temperature is measured between 15 and 20 degrees below zero.
However, plant survival and plant hardiness depend on a lot more than the average low temperature. Drought, snow cover, early or late frosts, wind and microclimates in your landscape play a huge role.
Bottom line. If you really want to plant that zone 5 plant, then give it a try, but don’t expect miracles!
Buddleia, Butterfly Bush ‘Buzz Midnight'
Carry on,
