The 2023 USDA plant hardiness zone map shows the areas where plants can be expected to grow, based on extreme winter temperatures. Darker shades (purple to blue) denote colder zones, phasing ...

Daly agrees. Assigning plant hardiness zones and the reasons the 30-year data led to a half-zone shift is too complex to attribute to one cause, such as climate change, he says.

The 2023 USDA plant hardiness zone map shows the areas where plants can be expected to grow, based on extreme winter temperatures. Darker shades (purple to blue) denote colder zones, phasing ...