USDA Has Changed What Planting Zone We’re In

Last month the United States Department of Agriculture changed our plant hardiness zone. One day we were in zone 8B. The next morning we woke up in zone 9A. Does that mean we can now plant citrus and avocado trees in the ground? Don’t start digging holes just yet.

So what does this mean? First we need to understand the USDA Hardiness Map. The map divides the country into 13 “hardiness zones.” These zones designate different ar-eas of average annual extreme minimum temperatures. Each numbered zone is separated by 10ºF. Within each zone there are also “half-zones” represented by the letters “a” and “b” which are separated by 5ºF. These zones help gardeners determine what kind of plants will survive in their climate. It mostly applies to perennial plants that need to survive the winter. But the information is also useful in selecting winter annuals, especially in the Southern United States where the winters are relatively mild.

Most of Fayette County except the extreme southern edge used to be in zone 8b, which has an average annual minimum temperature of between 15-20ºF. The USDA has now designated all of the County as zone 9a, which has an average annual minimum temperature of between 2025ºF.

Why did it change? USDA says the 2023 map is based on 30-year averages of the lowest annual temperature. When the map was last updated in 2012, the USDA data included several extremely cold winters during the 1980s. I was just a child at that time, but I remember it snowing enough in Schulenburg for my family to build a snowman in front of my grandparents house. I remember my father and grandfather breaking ice in water troughs and stock tanks so the cows could drink. My wife Janessa, who grew up in the Rio Grande Valley, remembers her family helping some orange growers build bonfires in their orchard to protect the trees from frost.

We’ve seen a few cold winters since then – most notably the 2021 winter storm. But according to the USDA’s data, the weather has gotten slightly warmer here.

How does this affect gardeners? Probably not a lot. We were already on the southern edge of zone 8b before the new map was published. The dividing line used to be just south of Schulenburg. So what about my initial question – can we now grow citrus in the ground? It depends on how much risk you are willing to take.

There used to be a large satsuma tree in Hallettsville, and it might still be there. It certainly managed to survive many winters. But city streets and stone buildings create a much warmer microclimate than areas out in the country. That’s why Houston gardeners can grow tropical plants year-round. But then again, there’s also an old lemon tree in Winedale, much farther to the north. Some plants can acclimate themselves to a cooler environment than they can normally survive.

It’s usually a good idea to select dwarf citrus varieties for growing this far north. Smaller trees are easier to cover and protect in cold weather.