USDA’s New Plant Hardiness Zone Map – It’s Not What You Think It Is!

USDA Plant Hardiness Zone MapPlant hardiness zone map should be called cold weather map.
* What it really does is predict the ‘lowest/coldest’ temperatures you can expect in your planting zone.

*What it ‘Does Not Do‘ is forecast your first or last average frost dates in your planting zone! Find Your First and Last Average Frost Dates

Federal “plant hardiness map was updated for the first time in two decades, revealing many areas where the coldest day of the year isn’t as cold anymore.

For example, Des Moines, Iowa, used to be in zone 5a, meaning the lowest temperature on average was between minus 15 and minus 20 degrees Fahrenheit. Now it’s 5b, which has a coldest temperature of 10 to 15 degrees below zero.

A key change in the update is using average temperature records from 1976-2005 instead of the earlier 1974-1986. The nation’s average temperature from 1976 to 2005 was two-thirds of a degree warmer than for the old time period.

It’s important to recognize that the plant hardiness map represents the extreme coldest temperature a location experiences each year, averaged over a period of years. It is really an extreme cold map and doesn’t track average temperatures.

The more recent averaging period has generally caused a one 5-degree half-zone shift to the warmer side over much of the U.S.

USDA Undersecretary Catherine Woteki called it “the most sophisticated Plant Hardiness Zone Map yet for the United States” but made no mention of climate change. USDA spokeswoman Kim Kaplan distanced the map from global warming issues. Even though much of the country is in warmer zones, she said, the map is not a good instrument to demonstrate climate change because it is based on just the coldest days of the year.

At a time when the ‘normal’ climate has become a moving target, this revision of the hardiness zone map gives us a clear picture of the ‘new normal,’ and will be an essential tool for gardeners and farmers.

Highly Recommended USDA Plant Hardiness Zone Map

Why is common sense so uncommon?
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