Climate change is forcing tweaks to a vital map for farmers and gardeners

Warming temperatures are changing where and when different plant varieties can grow most successfully, according to a U.S. Department of Agriculture (USDA) map released this week.

Why it matters: The Plant Hardiness Zone Map is a kind of bible for farmers and gardeners, helping them understand which plants can thrive in their area — and when to plant them.

• The new zones are particularly significant for those already growing plants at the extreme edge of their suggested range.

How it works: The map divides the U.S. into 13 zones, each representing a range of 10 degrees Fahrenheit.

• Each zone is divided further into two five-degree half zones.

Zoom in: The new zones are based on the average annual extreme minimum winter temperature from 1991–2020.

• The previous map, released in 2012, was based on 1976–2005 data.
• "The annual extreme minimum temperature represents the coldest night of the year, which can be highly variable from year to year, depending on local weather patterns," per USDA.

The upshot: Areas in the Midwest and Great Plains warmed the most, shifting them into warmer half zones.

• And the Pacific Northwest's growing season may last longer than in years past.

Yes, but: Many factors influence whether a given plant grows successfully or not, including light, soil moisture, humidity and exposure to the elements.

• The USDA recommends consulting with local producers, nurseries or master gardeners for area-specific growing advice.

The bottom line: You don't need to start changing which plants you're growing — thriving plants will likely continue to grow successfully.