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  • Rick Bonetti

New Plant Hardiness Map Shifting Toward Higher Temperatures


USDA Plant Hardiness Zone Map, 2023. from the Agricultural Research Service, U.S. Department of Agriculture. Accessed from https://planthardiness.ars.usda.gov/


The 2023 interactive edition of the USDA Plant Hardiness Zone Map (PHZM) is now available online here. "The new PHZM is generally about one quarter-zone warmer than reported in the 2012 PHZM throughout much of the United States." But since the USDA PHZM represents 30-year averages of what are essentially extreme weather events and climate changes are usually based on trends in overall annual average temperatures recorded over 50-100 years, the USDA is careful to disclaim that "changes in zones are not reliable evidence of whether there has been global warming." You be the judge.


GIS data can now be downloaded directly from the PRISM Climate Group at Oregon State University (OSU). "All Plant Hardiness Zone Maps (PHZM) should serve as general guides for growing perennial plants. They are based on the average lowest temperatures, not the lowest ever.


In 2021 PRISM released 30-Year Normal Precipitation maps based on datasets from 1991-2020 describing average monthly and annual conditions over the most recent three full decades. PRISIM;s Drought Indicator shows much of western Oregon in yellow at 70-90% precipitation this past 12 months compared with long-term (30-Year) averages.


This new 2023 version of the Plant Hardiness Zone Map has several interactive features. In addition to the capabilities listed above, there are several "widgets" that can be found below the Zip Code Search in the map.


Most of Rogue Valley is now in zone 8a (15-20 degrees F), with surrounding hill/mountain areas and Ashland in zone 8b (10-15). An earlier 1990 PHZM map showed Medford in zone 7b (5-10 degrees F)! Brookings OR is now zone 10a.


Jackson County Master Gardeners (Oregon State University Extension Service) is having a 2024 Master Gardener Class Interest Meeting on December 13, 2023 from 10- 11 a.m. PT in Central Point, OR.


The Jackson County Master Gardener Association chapter of the OSU Master Gardener™ Program also has a separate website. to help us "Learn, Practice, and Teach the Art and Science of Gardening in the Rogue Valley". They have a virtual tour of native plant gardens across the Rogue Valley to help us adapt to climate change.



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