The New USDA Zone Map-What it means to Your Garden Now

This week the USDA released a new Plant Hardiness Zone Map in the United States. And it's all due to Global Warming, right? Well, not exactly. Here is the new national map with "halfzones" noted, in other words to regions of five degrees Fahrenheit either way- According to the official USDA Website,differences in length of time of recording conditions and more technologically elaborate reporting play a part in the current rendering of zone differences:

Compared to the 1990 version, zone boundaries in this edition of the map have shifted in many areas. The new map is generally one 5-degree Fahrenheit half-zone warmer than the previous map throughout much of the United States. This is mostly a result of using temperature data from a longer and more recent time period; the new map uses data measured at weather stations during the 30-year period 1976-2005. In contrast, the 1990 map was based on temperature data from only a 13-year period of 1974-1986.

Some of the changes in the zones, however, are a result of new, more sophisticated methods for mapping zones between weather stations. These include algorithms that considered for the first time such factors as changes in elevation, nearness to large bodies of water, and position on the terrain, such as valley bottoms and ridge tops. Also, the new map used temperature data from many more stations than did the 1990 map. These advances greatly improved the accuracy and detail of the map, especially in mountainous regions of the western United States. In some cases, advances resulted in changes to cooler, rather than warmer, zones.

Because of my location in the Missouri Ozarks, this post will deal with Missouri. You can download the map for wherever you live in the United States here. The region which includes Missouri, is the North Central region. Here's that map: What does it mean to you as a gardener? The main differences that I can readily see are:

• Some of Southern Missouri is now Zone 7!
• Some of Southern Missouri is 6b where it was formerly 6a. And so forth.
• With 13 zones in the United States, and these halved to "a" and "b" zones you can pretty quickly see that Missouri is still considered moderate in climate here compared to the rest of the US.
• This will make a difference in some species of plants for your garden, or at least in some cases, in more options for you.
• If over the years, you've had to rule out some "borderline" plants that you love, regroup! Compare your plants/plant packets with the zone numbers and don't rule out any species until you do that comparison.

Here is the State of Missouri with its shiny new zone designations! :) The USDA cites other uses for these zone maps too. They are important on several scientific levels:

While about 80 million American gardeners, as well as those who grow and breed plants, are the largest users of the USDA Plant Hardiness Zone Map, many others need this hardiness zone information. For example, the USDA Risk Management Agency uses the USDA plant hardiness zone designations to set some crop insurance standards. Scientists use the plant hardiness zones as a data layer in many research models such as modeling the spread of exotic weeds and insects.

Enjoy your weekend, and keep poring over those seed catalogs! :) ~JB The United States Department of Agriculture website is referenced in the above included images and blockquotes.