Nov 22, 2023 - News

How plant hardiness is changing California landscaping

Data: Axios analysis of USDA data; Map: Will Chase/Axios
Data: Axios analysis of USDA data; Map: Will Chase/Axios

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 last 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.

Catch up quick: The map was last published in 2012, based on 30 years of average annual low temperatures between 1976 and 2005.

  • The new map — showing the coldest average temperatures have crept up about 2.5° F across the U.S. — taps data from 1991 to 2020 and information collected from over 13,000 weather stations, Axios' Emily Harris reports.
  • That's nearly double the data collection points compared to the previous map — improving the accuracy of the new one.

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

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

State of play: While the new map for Northern California shows little change overall, some locations shifted a half-zone higher or lower depending on the microclimate, including parts of the Bay Area.

  • That means the new zones will be particularly significant for those already growing plants at the extreme edge of their suggested range.

The big picture: Farmers in California have taken steps in recent years to experiment with new crop varieties that can better withstand drought and heat amid climate change impacts.

  • That includes mango trees and tropical palms like the ones found at Richmond-based plant nursery Golden Gate Palms.

Of note: Many factors influence whether a given plant grows successfully, 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 San Francisco Department of Public Works maintains a list of drought-tolerant plants recommended for landscaping.

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

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