USDA ZONE MAP
Not sure which zone you’re in? Click HERE to find out, and include your zone number when sending in a comment or question.
Originally developed in the 1940s, the USDA Zone Map was revised in 1990 (and is about to be revised again). It divides the U.S. into 11 zones, each of which represents a 10-degree Fahrenheit difference in the average minimum winter temperature. Each zone is further divided into A and B regions based on 5-degree differences.
The information is useful, but it shouldn’t be taken too literally. Various factors can affect a plant’s ability to survive on the edge of a zone – the buffering effects of a nearby lake, altitude, rainfall, soil type and composition, and exposure. In other words, microclimates. And in many cases the information regarding a plant’s hardiness is purely anecdotal, which is to say it hasn’t been determined scientifically. So, if you live in Zone 6a, chances are you can grow plants rated in Zones 5b through 7a. I wouldn’t try to push it much more than that, even though I do all the time, not always with success.
By the way, I now garden in Zone 6b, although before 1990, Tulsa was in Zone 7. I’ll never forget the calls I got from friends asking me whether all their plants were going to die following the revision! And guess what? Rumor has it that with the latest revision, Tulsa will be back in Zone 7, which is probably where it should have stayed all along. Good to know your tax dollars are hard at work, huh?
