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GRAND JUNCTION, Colo. — What do you think about the new USDA Hardiness Zone Map? Hardiness zone maps are what we use to determine the plants we should be planting in our gardens and yards.
This 2012 updated map shows much of the Grand Valley in hardiness zone 7a where the winter temperatures are supposed to be no lower than zero degrees F. This map is reported to be based on the lowest daily minimum temperature recorded for the years 1976 through 2005.
The USDA website says “this does not represent the coldest it has ever been or ever will be in an area, but it simply is the average of (the) lowest winter temperatures for a given location for this time period.” That doesn't really help much does it? Average means it can be warmer or colder so if you consider zone 7a as the hardiness zone you should use when selecting your plants you will eventually be disappointed. It will get colder and you will lose those plants.
The older USDA hardiness map issued January 1990 shows most of the Grand Valley as zone 6b, zero to -5 degrees F. Only a small section of Mesa County was in zone 7a and that was in the Palisade area. The 2006 Arbor Day Foundation hardiness map has most of the Grand Valley in zone 7 with temperatures between zero and 10 degrees F. So what should you believe? Is the Grand Junction area in zone 7, 7a or 6b?
Data provided by the National Arbor Day Foundation reports much of the United States experienced a change in hardiness of one to two zones between 1990 and 2006. This increase in temperature was due to climate change. Their data, however, shows no change in the hardiness zone for much of the Grand Valley.
Areas in the Grand Valley do have microclimates where zone 7a plants will do well. For most areas, however, you will be taking a chance if you plant zone 7a plants. If you remember the winter of 2009-2010, you may also remember that many of the Blue Atlas Cedars in our area were badly damaged as a result of that winter, yet this tree is reported to be hardy in Zone 6a (-10 F.) We lost a 30-foot Blue Atlas Cedar at the Mesa County Fairgrounds due to that winter's low temperatures. The hours of deep cold, the snow cover, and other factors also need to be figured in when determining hardiness zone designations.
Even with the new USDA Hardiness Zone Map showing our area as zone 7a, I would suggest you stick to plants with a lower cold tolerance. If you want to experiment with zone 7a or warmer plants, you might want to have a fr
ost blanket available for those winters when the temperature drops below zero degrees F.
If you want to check out the new 2012 USDA Hardiness Zone and compare it with the 1990 USDA map and the Arbor Day Foundation maps you will find these on my website at http://WesternSlopeGardening.org.
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Dr. Curtis E. Swift is the area horticulture agent with the CSU Extension. Reach him at Curt.Swift@mesacounty.us, visit WesternSlopeGardening.org, or check out his blog at http://SwiftsGardeningBlog.blogspot.com.
This 2012 updated map shows much of the Grand Valley in hardiness zone 7a where the winter temperatures are supposed to be no lower than zero degrees F. This map is reported to be based on the lowest daily minimum temperature recorded for the years 1976 through 2005.
The USDA website says “this does not represent the coldest it has ever been or ever will be in an area, but it simply is the average of (the) lowest winter temperatures for a given location for this time period.” That doesn't really help much does it? Average means it can be warmer or colder so if you consider zone 7a as the hardiness zone you should use when selecting your plants you will eventually be disappointed. It will get colder and you will lose those plants.
The older USDA hardiness map issued January 1990 shows most of the Grand Valley as zone 6b, zero to -5 degrees F. Only a small section of Mesa County was in zone 7a and that was in the Palisade area. The 2006 Arbor Day Foundation hardiness map has most of the Grand Valley in zone 7 with temperatures between zero and 10 degrees F. So what should you believe? Is the Grand Junction area in zone 7, 7a or 6b?
Data provided by the National Arbor Day Foundation reports much of the United States experienced a change in hardiness of one to two zones between 1990 and 2006. This increase in temperature was due to climate change. Their data, however, shows no change in the hardiness zone for much of the Grand Valley.
Areas in the Grand Valley do have microclimates where zone 7a plants will do well. For most areas, however, you will be taking a chance if you plant zone 7a plants. If you remember the winter of 2009-2010, you may also remember that many of the Blue Atlas Cedars in our area were badly damaged as a result of that winter, yet this tree is reported to be hardy in Zone 6a (-10 F.) We lost a 30-foot Blue Atlas Cedar at the Mesa County Fairgrounds due to that winter's low temperatures. The hours of deep cold, the snow cover, and other factors also need to be figured in when determining hardiness zone designations.
Even with the new USDA Hardiness Zone Map showing our area as zone 7a, I would suggest you stick to plants with a lower cold tolerance. If you want to experiment with zone 7a or warmer plants, you might want to have a fr
ost blanket available for those winters when the temperature drops below zero degrees F.
If you want to check out the new 2012 USDA Hardiness Zone and compare it with the 1990 USDA map and the Arbor Day Foundation maps you will find these on my website at http://WesternSlopeGardening.org.
--------------------------------
Dr. Curtis E. Swift is the area horticulture agent with the CSU Extension. Reach him at Curt.Swift@mesacounty.us, visit WesternSlopeGardening.org, or check out his blog at http://SwiftsGardeningBlog.blogspot.com.
