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Maps reveal new plant hardiness zones

Gardeners rely on a number of factors when deciding on what to plant in their gardens and around their property. One of the most important things to take into consideration is the climate.

Since 1960, the go-to source for climate and relation to agriculture has been the U.S. Department of Agriculture's (USDA) Plant Hardiness Zone map. In 1967, Agriculture Canada developed their own map that took into consideration Canadian plant survival data and a wider range of climatic variables. The maps remained constant until now.

In January 2012, the USDA released an updated zone map. The map is now more precise and reflects microclimates, heat islands, prevailing wind, elevation, and generally better data. It breaks down the country into 13 unique zones from the previous 11. Individuals who once resided in a particular zone may find that they are now moved into another zone. This updated map has taken into consideration climate changes that have occurred between 1976 and 2005. You now may be able to try plants that you may have been skeptical about in the past.

The new map now offers a Geographic Information System, orGIS, -based, interactive format and is specifically designed to be Internet-friendly. The map website also incorporates a "find your zone by ZIP code" function. Static images of national, regional and state maps have also been included to ensure the map is readily accessible to those who lack broadband Internet access.

The new version of the map includes 13 zones, with the addition for the first time of zones 12 (50-60 degrees F) and 13 (60-70 degrees F). Each zone is a 10-degree Fahrenheit band, further divided into A and B 5-degree Fahrenheit zones.

A hardiness zone describes a geographically defined area in which a specific category of plant life is capable of growing, as defined by climatic conditions, including its ability to withstand the minimum temperatures of the zone. Summer temperatures are not factored into the mix. Therefore, areas with similar winter patterns and average lows may be in the same zone despite having drastically different highs. Hardiness zones may not take into consideration snow cover, either. Snow helps insulate the soil and hibernating plants. Therefore hardiness zones are more like guidelines instead of foolproof methods of determining viable plants.

Although a poster-sized version of this map will not be available for purchase from USDA, as in the past, anyone may download the map free of charge from the Internet onto their personal computer and print copies of the map as needed.

When shopping for plants, most will display a hardiness zone right on the container to help you determine whether this particular plant will be acceptable outdoors in your zone. To learn more about hardiness zones, visit or