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Hardiness zone maps

January 20, 2011
By Stephanie Bethke-DeJaeghere

There may be some confusion out there in regard to maps this year. It will depend on which map you are looking at, in which catalog and to what it refers to. What am I talking about? Hardiness zone maps.

We generally use the USDA map to define which zone we are in which helps us to determine which plants that we can grow here and expect to do well. The particular area in which we live is in Zone 4b with some areas closer to us actually in Zone 4a.

The National Arbor Day Foundation (NADF) places our particular growing area in a Zone 5 growing area. The NADF is using the past 15 years to determine what zone goes where on these maps. The growing conditions from this period of time, as we all know, have been warmer then what we have been used to. The USDA maps are also complied on a small amount of information but not recent information (1974-1986). So, which do we believe?

First, you will need to read the small print in the catalog or wherever you are purchasing your plants, particularly perennial plants, trees, shrubs and so forth. You need to know which map you are looking at.

The U of M is telling us to use caution no matter which map you decide to use. We all want to try that Zone 5 plant at times. We all know that any plants survival depends greatly on much more then how cold the temperatures will be that certain winter. For example, when it gets cold like it has been this past week is probably not such a big problem for plants that are covered well with mulch and have a little bit of snow piled on top.

For those plants that are left exposed and have very little snow on top to help protect it from the cold temperatures, these will experience the most possible damage. I have more fear for the springtime thaw and freezing that we can experience in our region.

The heaving that can occur to the plants during this time has a lot more impact on plants then the colder temperatures in January and February. If plants are coming up in the spring and we get a sudden cold snap where it seems that Mother Nature is reverting to winter again, this is where we can lose more plants from the weather.

If you want to try your hand at growing Zone 5 plants and I think most of us probably have tried at one time or another, then go ahead and do it. The advice from the U of M is to try with our typical garden plants (perennials) and not the more expensive plants such as trees and shrubs. If the perennials can't seem to make it in your garden, it is best to spend your money on more reliable trees and shrubs for your growing area.

You may find that you can grow some of the Zone 5 plants as long as you are prepared to do the extra work in the fall, to keep the plants prepared for the winter months ahead. You may find that you don't like to do the extra work required for some plants and may choose not to grow them if they don't make it through the next winter.

I like to think of Zone 5 plants as a scientific experiment. It may be a successful experiment and it may be one that does not pan out what so ever. If you try one or two plants over a length of time, such as two or three years, then go for the more expensive plants or more expensive group plantings.

For more information on gardening, you can reach me at



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