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Thursday, March 22, 2012

USDA Plant Hardiness Zone Map 2012

New Plant Hardiness Zone Map for 2012

You may have noticed the U.S. Dept. of Agriculture has revised the Plant Hardiness Zone Map this year, the first revision in a decade or more. The Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a particular location. The Map is based on the average annual minimum winter temperatures, which are divided into hardiness zones. For the first time, the Map is available as an interactive map accessible on your computer. You can view the map by state as well as type in your zip code to see the hardiness zone for your specific location. The drawback to the Map is the hardiness zones, based on minimum cold temperatures, do not take into account the summer heat levels, which can actually be more important information than the low temperatures are, to gardeners.

When I moved to the farm in 1979 I was fully in hardiness Zone 6. All of Southern Missouri was in that zone. Over time the weather patterns have changed. It wasn’t unusual to have -5 degrees F. here, or lower, in winter. That’s unusual now. The new USDA Map has southern Missouri now fully in Zone 6b, with the Bootheel in 7a. What that means for gardening is a number of plants that couldn’t survive our winters 30 years ago, will survive and grow now.

Figs, which I’ve written about many times here, are doing fine. Muscadines, that Southern version of a grape-relative, thrive in our newer climate. Herbs such as Mexican mint marigold (Tagetes lucida) won’t live in Zone 6, but are now fully hardy in my garden. This year, I even have lemongrass -  coming back again, having lived through our mild winter (although I don’t expect that every year).
American Horticulture Heat Zone Map

The Heat Zone Map was created under the direction of an acquaintance of mine, Dr. Marc Cathey, for the American Horticulture Society a few years ago. It is based completely on maximum summer heat temperatures for all regions of the U.S., just as the Cold Hardiness Map. It’s a good idea, when trying to figure out what plants will do well in your garden, to consult both the new USDA Plant Hardiness Zone Map, for cold, as well as the AHS Heat Zone Map. The two maps give a good balance than either by itself.

I still think we may have a cold snap before our last frost date this year, but I’m just as convinced the earlier I can get my garden planted, the better the chance of success. If we have another summer like the past two, then an early spring garden, and a late fall garden will be more rewarding than expecting everything to produce in the summer.

Water standing in pathways on first day of Spring.

Sunlight on far hill after rains.

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