The USDA announced changes in plant hardiness zones this week, moving San Antonio into the same planting zone as Houston and Corpus Christi while Austin, Dallas and Houston zones remain unchanged. The backsides of seed packets will never be the same.
The new map reflects 30 years of temperature data, from 1976 – 2006, and includes 26 specific zones, each with a five-degree temperature differential.
For example, San Antonio moved from zone 8b, with annual lows of 15 – 20 degrees, to zone 9a, with annual lows of 20-25 degrees. Of 34 cities listed on the key of the map, 18 have new zoning designations.
Here’s the new zones for the four largest Texas cities:
- Dallas–Zone 8a, 10-15 degrees
- Houston–Zone 9a, 20 – 25 degrees
- San Antonio–9a, 20 – 25 degrees (from 8b)
- Austin–8b, 15-20 degreees
The new maps employ useful new interactive GPS, whereby you can plug in your zip code and find out your zone. The data also reflects microclimate effects like nearby water sources and elevation.
The redefined heartiness zones tell us what butterflies and blooms have been communicating for the past few years. As Monarchs and other butterflies reproduce on the San Antonio River well into the winter, it’s apparent that it’s just not as cold as it used to be.