Gardening has been a lifelong passion for Wende and she’d like to share her passion with her readers. Follow her as she writes about her gardening adventures, lists tasks to do depending on the season, and gives easy to understand gardening advice.
Great News! After 20 years, the USDA has updated the Plant Hardiness Zones! Beware, our Zone 4 (or 5 depending on where you live) has now become Zone 5b (-15 to -10F). The new 13 zone map has been brought into the internet age with GIS-based interactive maps and more accurate zones that take into consideration things like elevation, terrain, and closeness to bodies of water. Using a 30 year timespan (unlike the 1990 version that used a 13 yr span), many more weather stations, and expert input from the climatic and horticultural community, the map is much more accurate than it was plus it shows a 5 degree increase (warmer) overall for the US.
Zone 5b's limits go just west of Waukesha, where it becomes 5a (colder!). Plant hardiness zone designations represent the average annual extreme minimum temperatures at a given location during a particular time period - emphasis on average. They do not represent the lowest temperatures that can happen.
Although home gardeners are the biggest users of this map, it is also used in insuring crops, scientific research like insect and weed dispursement modeling, and also for forecasting of products and services that are affected by weather.
Of course, we gardeners know what plants thrive in our WI winters because those winners are living happily in our yards. I hope that when plants are labeled for sale this spring they will have the new zones on them and that it doesn't create too much confusion. Nurseries will need to educate their employees and be ready to do a lot of explaining for customers.
interactive map: http://planthardiness.ars.usda.gov/PHZMWeb/Default.aspx