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National Arbor Day Foundation Introduces Arborday.org Hardiness Zones Map

date 03/15/02



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Arbor Day Foundation
Anthony Marek

Nebraska City, Neb.- Much of the United States has been warmer in recent years, and that affects which trees are right for planting.

Thanks to The National Arbor Day Foundation`s new Arborday.org Hardiness Zones map, if you live in Tulsa, Oklahoma, you`ll know to plant trees appropriate for zone 7 instead of zone 6. If your home is St. Petersburg, Florida, you`ll now plant trees for zone 10 instead of 9. And if you`re from Akron, Ohio, your correct zone is now 6, not 5.

These are just some of the changes described by the Arbor Day Foundation`s new Arborday.org Hardiness Zones map, accessible at the Foundation`s Web site, arborday.org. Completed in 2002, the map/Web site combination offers more current and precise information on cold-hardiness zones, a key factor in selecting trees for planting.

A hardiness zone is the area defined by a range of average annual minimum temperatures. For example, the average annual minimum temperature in zone 5 is -10 to -20 degrees Fahrenheit; zone 7 is 10 to 0 degrees, etc.

The Arborday.org Hardiness Zones map is based on the most recently compiled average annual minimum temperatures recorded by U.S. weather stations. By entering their five-digit zip code, visitors to the Foundation`s arborday.org Web site can pinpoint hardiness information for their location. The arborday.org site also has information about which trees are hardy for planting in the different zones.


"We want to provide Arbor Day Foundation members and the general public the best possible information to help them be successful in planting trees," John Rosenow, Foundation president, said. "Providing the zone information for individual zip codes on our arborday.org Web site makes it possible for people to obtain the most precise data available."

Source data was taken from more than 5,000 National Climatic Data Center cooperative stations across the continental United States that had recorded average annual minimum temperatures, according to Roger Day, information systems manager at the Arbor Day Foundation and the project manager for the creation of the map. Once this data was analyzed, the hardiness zones were revised, generally reflecting warmer recent temperatures in some parts of the country. This was especially noticeable in the Midwest and Central Plains, Day said.

The need to reflect climatic change was one of the reasons given by the U.S. Department of Agriculture for the 1990 revision of its original hardiness zone map, first introduced in 1960. In constructing the Arborday.org Hardiness Zones map, The National Arbor Day Foundation found that climate changes also occurred into the late 1980`s and `90`s. The Foundation used the updated versions of the same sources of data as had been utilized by the U.S. Department of Agriculture in the creation of its hardiness zone maps.

"As a guide for planting trees, the Arborday.org Hardiness Zones refer only to a tree`s appropriateness for an area`s temperature extremes," Rosenow said. "Other factors such as moisture, soil, and sun requirements should also be considered, as well as microclimates within a hardiness zone."

The National Arbor Day Foundation is a nonprofit education organization dedicated to tree planting and environmental stewardship.