AUSTIN (KXAN) — As the United States continues to warm from heat-trapping greenhouse gas emissions, plants that would once thrive in a particular area and latitude are no longer surviving. Instead planting zones as a whole are shifting northward. This in return is forcing farmers and gardeners to adapt to their changing climate.

According to the United States Department of Agriculture (USDA), “hardiness zones are used to indicate where various permanent landscape plants can adapt. If you want a shrub, perennial, or tree to survive and grow year after year, the plant must tolerate year-round conditions in your area, such as the lowest and highest temperatures and the amount and distribution of rainfall.”

Their map is based on the average annual minimum winter temperature. It has a total of 26 zones that are each separated by temperature intervals of 5 degrees.

Our partners over at Climate Central found that these planting ‘hardiness’ zones are shifting northward across the United States over the course of the last two 30-year average periods.

Their study showed that of the 242 US cities analyzed across the country, 231 or 95% of them, experienced warming of their average annual minimum temperature. According to Climate Central, these 231 locations warmed by 3.3°F on average since the 1951-1980 period. This warming is responsible for the shifting plant zones.

Plant zones based on 30 yr average annual minimum temps
Plant zones based on 30 yr average annual minimum temps

Why this is important

These zones not only designate which plants can survive during the harsh winters of a specific geographic location but also help in determining the survivability of certain ecosystems including the wildlife and insects that rely on those plants to survive. According to Climate Central, the USDA also uses plant hardiness zones to set crop insurance standards.

Where does Austin stand?

Shifting planting zones

The city of Austin, among much of the rest of the country, is experiencing the change as well. Over the course of 70 years, as our climate warms, we have shifted from ‘Zone 8’ to ‘Zone 9’. Again, these zones distinguish which plants can grow and thrive in different parts of the country.

What are the differences between these two zones?

Not only are the zones distinguished by the average minimum temperatures but they are also separated by the first and last freeze or “growing season”.

Zone 8 (10 to 20°F) has an average first freeze date of Dec 1 and an average last frost date of April 1.

Zone 9 (20 to 30°F) has an average first freeze date of Dec 15 and an average last frost date of March 1.

Nearly a full month and a half longer growing season!

Plants that thrive in Zone 8:

  • Watermelons, tangerines, bee balm, succulents, tulips, jasmine, lilies, carrots, peas, celery, spinach, asparagus & collards to name a few.
  • Many herbs, including thyme, rosemary, and hibiscus.

 Plants that thrive in Zone 9:

  • Chives, kiwi, okra, roses, daffodils, dahlias, snake plants, begonias, eggplant, kale, cucumbers, leeks, onions, carrots and turnips to name a few.