Since we are in the middle of one of our winter cold snaps, this seems like a good time to talk about USDA growing zones, especially since the USDA recently updated its Plant Hardiness Zone Map for the first time since 2005.

If the USDA growing zone map is new to you, now is a good time to learn about it since we are likely to lose some plants during this deep freeze.

Previously, Tulsa was part of the grouping called 7a which meant that during the winter, our annual extreme minimum temperature on average should be somewhere between 0 and 5 degrees. Any of us who live here know that more often than not we have a few really cold days where we drop below those temperatures, but that’s the beauty of averages.

In the new 2023 map, Tulsa is now in growing zone 7b which means our annual extreme minimum temperatures on average are now 5 to 10 degrees. As you noticed, recorded temperatures are predicting warmer average winter temperatures. That being said, we will continue to have outlier years and events that dip below the predicted averages. This is part of the fun of living in Oklahoma. To explore the map yourself, just do an internet search for USDA Plant Hardiness Map.

Why does this matter to gardeners? Most plants or seeds you purchase come with growing zone information. If you purchase plants that are rated for our growing zone and lower (number wise) they will have a better chance of surviving our winters than if you were to purchase plants rated for zone 8 or 10 for example.

In spite of making good purchasing decisions, it seems like in the last few years we have experienced deep freezes that took out a lot of our plants that were appropriately rated for our growing zone. Many of us remember the deep freeze of a few years ago that almost wiped out our local crapemyrtle population. During that cold snap we got down to minus 15 for a while and that would be like what people living in Nebraska should expect during the winter. The crapemyrtles and other similarly rated plants didn’t like it very much and many of them threw in the towel.

So, what should we do now that we have updated growing zone information. First of all, we should purchase plants that are rated for our growing zone. These plants will do the best in our area.

Secondly, during this cold weather, most of us are not going to dig up and move our crapemyrtles indoors and understandably so, but if we do have potted plants outdoors that are marginal for our area, we should try to move them indoors during extremely cold weather.

The bottom line, buckle up. We are likely going to lose some plants this week. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo used with permission.