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Washington Voices

New plant hardiness map offers high-tech views

Thu., Feb. 2, 2012

On Jan. 25, the USDA Agricultural Research Service unveiled the new Plant Hardiness Zone Map to replace the 1990 map that has guided our selection of plants hardy enough to grow here.

Guess what; Spokane and much of the Inland Northwest has moved from Zone 5 to warmer Zone 6. Is this change all because of climate warming?

Only in part. What really changed was the technology used to create the map. The 1990 map was based solely on the lowest average minimum winter temperatures collected between 1974 and 1986. The new map uses geographic information system technology to refine 30 years of data between 1976 and 2005 from 8,000 weather stations to create a map that looks at zones in a very different way.

Scientists at Oregon State University’s Prism Climate Group collected the data and then used a mathematical algorithm to refine the temperature data with information on elevation, prevailing wind direction, topography and proximity to large bodies of water or urban cores to give a more rounded interpretation. The algorithm then tied each information point together to create the boundaries of the new zones. By using GIS technology, the new interactive map can be layered with other map information to allow the user to zoom right down to their neighborhood.

Here is how that works. To see the new map go to Hardzone. Click on the button that takes you to the new map. If all you want to do is check your new zone, enter your ZIP code in the box. The zone will appear along with a static map of the state.

If you want to use the interactive features, go to the “View Maps” tab at the top of the page. Once there, scroll down the left side of the page to the interactive map button. Enter the security code. When the U.S. map appears, go to the upper right hand corner of the page and adjust the sliding color transparency bar to the midpoint. Select which base map, terrain or satellite view, you want. This will layer the maps so you see all the terrain or structures and roads with the zone colors on top of them. Now click on the Spokane area and zoom in. Be patient, the download is slow and it doesn’t go as low as Google Maps. Find your neighborhood or house if you can see it and click on it. The box that pops up will show your zone and the actual minimum average temperature at that site. This lets you know if you are at the top or bottom of the range for the zone.

Don’t have a broadband connection? There are static maps available on the site too.

Does this change how we will garden? Probably not. Your knowledge of the conditions in your garden is still better than any map will ever be. It simply confirms all the cold and warm spots we are already aware of. We just don’t have to guess as much. It also gives us a whole new realm of possibilities to play zone denial with nature. Game on Mother Nature!

Pat Munts has gardened in the Spokane Valley for more than 35 years. She can be reached at pat@inlandnwgardening. com.

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