Its spring and you are a gardener heading out to buy plants. Someone warns you to choose plants for your “zone.” What is a gardening zone? If you are new to gardening you may be a little confused about all this zone stuff. A gardening zone is determined officially by the United States Department of Agriculture but a few other places have developed their own zone charts. The charts are revised every 10-15 years. The latest map was issued in 2012. Zone maps can help you decide what plants you should purchase for your garden.
How gardening zone charts work
A zone chart divides the country into areas by the coldest winter temperatures they may experience and numbers them. That’s called your winter hardiness zone for gardening. There’s another USDA zone chart for heat hardiness but it is little used. Each gardening zone may be further divided into part A and part B. The colder the winter, the lower the number assigned to the zone. In the US mainland area, we currently have zones three to eleven. For example in Michigan, the cold hardiness zones range from 6, in the Detroit area and along some southwestern coastlines, to 3, in tiny areas of the upper lower peninsula and the U.P. Currently most of Michigan is Zone 5 or 6.
The USDA gathers data from numerous places around the United States to determine an average maximum low temperature from an area. The newest gardening zone chart that the USDA published in 2012 has taken into consideration the data from a much greater number of places than previous zone maps. Even without climate change, the increased range of data may have changed the zone map from previous ones for your area. Always consult the latest zone map.
Where to find your gardening zone
Gardening zone maps are available from a variety of sources such as garden reference books available at your local bookstore or library, but these may be outdated. A great source for a free, up to date gardening zone map is your favorite gardening catalog. Here’s a link that will allow you to find your garden zone by state or zipcode. http://planthardiness.ars.usda.gov/PHZMWeb/
Some places devise their own gardening zone maps, such as the Arbor Day Foundation and Sunset Gardening Publications. Since most plant sellers use the USDA chart to rate the hardiness of their plants it’s probably best to look up your gardening site on the official USDA zone map.
How to Use the Gardening Zone Map Information
The gardening zone chart is used to inform consumers which perennial plants will survive the winter in their area. Most plant labels and gardening catalogs will put the zone hardiness rating somewhere in the plant description. When you choose plants for your garden choose plants that will grow in your zone or a lower numbered zone.
If you are a gardener in zone five you will want to choose plants that are rated hardy to zone five, four or three. (Zone three is about the coldest area of the mainland United States.) A plant rated hardy to zone seven would probably not survive the winter in your garden.
While most plants that have been in the market for a while will be assigned pretty accurately to their gardening zone, new plants may be less accurately placed. When new plants are put on the market they will probably have been trialed in a number of places, but until thousands of gardeners are growing the plant, the information about their zone hardiness may be only a guess. When purchasing new plants, even new varieties of familiar garden plants, be aware that the zone hardiness may not be really accurate.
How to Cheat a Gardening Zone
What if you live in gardening zone five and you really, really, want a plant that is listed hardy to zone six. You may be able to cheat nature. In every yard there are areas we call micro-zones, areas where the climate is just a little different from the surrounding area. It may be up against the south side of the house, in a courtyard, or in a sheltered pocket surrounded by heat holding rocks or cement. A zone six plant might survive there.
There are other gardening tricks to try too. Deep mulching or a protective cover might do the trick. Sometimes plants that manage to survive a few milder winters in your zone will acclimate enough to survive a harsher one. Start with small plants of the variety you want to try and plant them in the spring. Only spend what you can afford to lose on the plant too.
If you have always wanted to grow certain types of plants in your garden but you don’t live in the right gardening zone, don’t despair. New varieties of the plant you are interested in may be developed that expand the gardening zone range.
And when you have been successful in getting a plant to grow in your gardening zone that wasn’t rated hardy for it, share the information with gardening friends and organizations. That may inspire others in your zone to grow the plant and ultimately get the gardening zone rating changed.
Here are some additional articles by the author that you may want to read.
How to prune spring flowering shrubs
How to grow trout lilies in the garden
Great native shrubs
You can read the authors weekly garden blog at