A new plant hardiness zone map released by the U.S. Department of Agriculture (USDA) will not only be of interest to gardeners, but anyone planting trees, shrubs or other ornamental plants. Since 1920, the USDA has published a Plant Hardiness Map that divides the country into 13 plant zones reflecting an average of minimum winter temperatures for a given location for the last 30 years. Zone 13 on the plant zone map reflects the warmest region indicating a warmer winter temperature limit of survival while Zone 1 reflects the coldest region indicating a colder winter temperature limit of survival. The USDA rating system was recently updated with data measured at weather stations during the 30-year period, 1976-2005.
So, what are the implications of the new USDA Hardiness Zone Map? Previously, the southern half of the state was in Zone 5 and the northern half was in Zone 4. Only a few counties in the northern Panhandle are in Zone 4 on the new map, or put another way, 90 percent of the state is now in Zone 5. Whether you agree or not, the new hardiness zone map does reflect a global warming trend, but more importantly to the gardener this information means planting marginally hardy plants like peaches and apricots, is less risky in most of Nebraska. An ornamental tree favored by many gardeners is the magnolia tree. Nurserymen have often considered one magnolia species, Magnolia acuminata, worth trying on protected sites in southeastern Nebraska. Armed with new USDA hardiness zone ratings, residents of central Nebraska may want to try planting this beautiful species. No doubt, many gardeners and landscapers will have their own list of favorite, but marginally hardy plants which now may be worth planting.
Even though the USDA rating system gives gardeners and landscapers a predictable temperature range for plants that might survive in each zone, don’t always accept the information as gospel. Remember the USDA system is based on average minimum temperatures and not on the extreme minimum temperatures that can occur in each zone. You may find this information along with the USDA zone recommendation on plant labels that you purchase at your local nursery or garden center. So don’t overlook all of this valuable information for your locale when predicting whether the plants you select will survive over many years.
Many variables, like extended drought prior to arrival of winter weather, will influence how well a plant withstands extreme winter conditions, so visiting with respected plant experts may help you make a wise decision. And speaking of wise decisions, please don’t overlook the possibility that your favorite plant is potentially invasive. Land managers already have a long list of noxious and invasive plants to battle, so please don’t plant a species that could one day overwhelm a local ecosystem.
If you really get into the USDA plant zone rating system, visit the interactive map at www.plantmaps.com/usda_hardiness_zone_map.php. Click on your location in the map and load your plant hardiness zone…pretty cool stuff!