Master Gardener: New plant hardiness zone – will it change how we garden?

Donna Tatting

Chisago County Master Gardener

In late January 2012, the United States Department of Agriculture released a new Plant Hardiness Zone Map.  It reflects the changes in temperature occurring across the country and how they will affect both garden and agricultural crops.  The map is made up of 26 geographical zones and it is the first time the map has been updated since 1990.

So what do these changes mean for us gardening in Minnesota ?  Well, not very much.

Unless you are part of the  “snowbird”  population which literally runs at top speed to the warmer southern climates right after Halloween and doesn’t return until April, you know that our winters are more mild than they used to be.

This winter aside, because I can’t even begin to express my delight in what’s currently going on here,  winters  just don’t seem as bad as they used to.  Oh, they can be bad, just not as much as bad.

Temperature changes of even 1 to 5 degrees overall can make a big difference in plant hardiness zones.  Most of the metro area is solidly in growing zones 4a and 4b.  The new map, however, now shows some zone 5 areas which for gardeners, does open up more plant choices.

These zone 5 areas are located well within urban areas which are influenced by  slope, elevation, soil conditions, proximity to bodies of water and urban “heat islands” caused by human activity.

For those of us who garden in Chisago County, little has changed.  I still recommend that plants labeled Zone 3 and 4 will have the best chance of survival and performance in your garden.

There are however, those wonderful little spots we call microclimates.  These are areas right within our gardens and around our home structure that provide a little something extra that allows even Zone 5 and 6 plants to survive our winters.

Now, I will admit, that we are truly pushing the envelope here, but I can use my own experience to prove my point.  In areas that are protected from harsh winter winds or benefit from the warmth of a building’s foundation, sometimes, these tender perennials can survive our winters.

I once had a butterfly bush, easily a Zone 5-6, that was planted up against a 2 foot wall, survive beautifully for 7 seasons.  The wall was also a collecting point for oak leaves that buried the bush heavily all winter giving added protection.

In the eighth year, the bush struggled to grow and never flowered.  By mid- summer, it was dead, but I always knew how lucky I was to have been able to grow that plant in that spot for so long.  The wall and the heavy leaf mulch had created a microclimate just right its survival.

So is there a bad side to these more mild winters here in Minnesota?  Lee Frelich, director of the Center of Forest Ecology at the University of Minnesota, notes there will be changes as far as plants that are native to the region.

We’ll probably have more pests which could not previously survive our winters and they will certainly do their damage.  In the forested areas, some trees will take over for others and that will affect wildlife.  Overall, the climate changes are good for some and bad for others.

To view the new Plant Hardiness Zone Map, search the internet for New USDA Plant Hardiness Map and you will find lots of images of this map.  You can even narrow it down to just the Minnesota map.

To really kick start your gardening season, don’t forget the upcoming Chisago County Master Gardener Spring Bonanza on March 10, in Center City.  For more information on this annual event and information on our Spring Series of Gardening Classes, call 651-277-0151.


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