bees and agriculture

USDA updates hardiness zones

Last Wednesday the USDA released its newly redrawn Plant Hardiness Zone Map. The map is based on the average lowest winter temperature in a given area—not the lowest temperature ever—and is calculated from data collected over the last 30 years. The new map was compiled at Oregon State University using GIS software.

Plant Hardiness Zones are used by gardeners, nurseries, farmers, or just about anyone who wants to know if a particular plant will thrive in a particular area. They are also used by scientists studying changes in animal distribution or the spread of invasive species, insects, and plant pathogens. A variety of federal and state agencies also use the information for projects and predictions.

The USDA is careful to say that the new map is not useful for studying climate change, and it points out the many of the changes in the map are due to better technology and better data manipulation. However, it is interesting to note that many areas in the United States were bumped into a warmer zone, and two new zones were added at the high end of the scale. The new zone 12 has average low temperatures of 50-60°F, and the new zone 13 has average low temperatures of 60-70°F.

It seems to me that if the changes were due solely to better data collection, the changes would occur in both directions—some areas would drop into a colder zone, some would rise into a warmer zone, and some would remain the same. But according to the sources I’ve read, the changes were nearly all in the warmer direction. And if two warmer zones had to be added—not just one—it means that some areas have average low winter temperatures that are more than 10 degrees warmer than previously calculated. That’s hard to explain by bad data.

The warmer map has several implications for beekeepers. For one thing, flowers may bloom earlier than they used to, especially in northern areas, and the growing season may be slightly longer. The mix of available forage may change as plants, previously confined to the south, slowly expand their distribution. The bad news is that warmer winter temperatures allow the spread of insects such as small hive beetles and wax moths that are routinely killed by freezing temperatures. Even the northern spread of Africanized honey bees can be accelerated by slightly warmer winter temperatures. All very interesting . . . and all very messy.


Follow this link to the interactive map where you can enter your zip code to find the details of your hardiness zone.

New USDA Hardiness Zones 2012


  • In our area, warmer often translates to wetter (if that is even conceivable, we’re already at 100-120 inches a year). So things may bloom earlier, but the rain may keep the bees indoors.

    I found the new zones quite surprising for our locale. With the old zones, we were on the border of 6 and 7, and I usually used 6 as a guideline. With the new zones, we are 8a. Wow, sounds almost tropical. This, of course, does not account for the unique microclimate of our property, which still has 6 inches of ice and slush on the ground.

    • Gretchen,

      We went from 7b to 8a, but I have always used 8 as my guideline because it seemed right to me. Now it’s official. I agree the rain is what keeps the bees inside around here. Today, my bees are out in force, even though we also have plenty of snow and ice remaining from the storm. I watched them carefully and they are bringing in no pollen. It goes to my theory that warm winter bees waste a lot of energy looking for something that’s not there, but at least they can do those cleansing flights. I will have to make more sugar patties, just in case. It’s still only January . . .

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