The USDA has for the last several decades established cold hardiness zones for our plants. These zones are our guidelines to what plants will do well in our area. The Plant Hardiness Zone Map divides the United States and Canada into 11 areas based on a 10 degree Fahrenheit difference in the average annual minimum temperatures. While the Tyler area is on the border line between 7b and 8a, most of the area is in Zone 8a which means our coldest average temperature for plants would be 10 to 15 degrees Fahrenheit.

Using the USDA map as a base, the National Arbor Day Foundation (NADF) has updated its map. They studied the last fifteen years of temperature data from the National Oceanic and Atmospheric Administrationís 5000 climatic data centers and decided to make changes. According to their evaluation, they have moved Zone 7 up into Oklahoma and Zone 8 is now up past the Oklahoma border. The only Zone 7 remaining in Texas is the Panhandle. This move from the NADF would make our average temperature 15 to 20 degrees Fahrenheit.

While the USDA maps have not been changed, it would be wise to keep the NADF changes in mind when selecting plants. To check out their map for the new Arbor Day Foundation cold-hardiness zones go to

Linda Sargent, Smith County Master Gardener
Texas Cooperative Extension

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