Whether you’re an avid gardener or a first-time planter, the USDA Plant Hardiness Zone Map is a great resource when it comes to figuring out which plants are most likely to survive where you live. The map, updated in 2012 (it was previously updated in 1990), divides the United States into 13 separate zones representing regions of average annual extreme minimum temperatures. Each zone is a 10-degree Fahrenheit band that is further divided into 5-degree half-zones. The zones provide a reference for selecting plants that can survive low winter temperatures.
So, did the map change from 1990 to 2012? You bet. The updated 2012 Hardiness Zone Maps shows that several zones have shifted north across the United States and two new zones, 12 (50-60˚) and 13 (60-70˚) were added. The new map is generally one 5-degree half-zone warmer than the previous map throughout much of the United States, but some areas shifted to cooler zones rather than warmer ones.
In the 1990 map (based on temperature data from 1974-1986), Pennsylvania was mostly dominated by zones 5 (-10 to -20˚) and 6 (0 to -10˚). In the 2012 map (based on temperature data from 1976-2005), some new zones crept into Pennsylvania and old zones shifted. Zone 7a (0 to 5˚) appeared in Southeast Pennsylvania and zone 6 has taken over some areas that zone 5 previously covered, specifically in North Central Pennsylvania and Western Pennsylvania. These zone changes may not seem like much to us, but they can make a big difference for a plant. For example, Southern magnolias, which were previously limited in range from Florida to Virginia, can now thrive as far north as Pennsylvania.
Even if your zone has changed in the new map, the plants you have in your yard will most likely continue to thrive. But you may also be able to introduce some new plants to your garden. This is a great time of year to start planning a spring garden. Start by finding out which Hardiness Zone you live in with this interactive map. Then, search the Lady Bird Johnson Wildflower Center’s Native Plant Database to find plants that will thrive in your yard.
Once those plants start to bud and bloom, don’t forget to snap photos and share them with the Eyes on Central PA Mission on Project Noah!