The first daffodils have crept into flower and the snowdrops have peaked already. If you think winters aren’t what they used to be, you’re not alone.
Scientists at the U.S. Department of Agriculture on Wednesday released a plant hardiness zone map of the nation that shows generally warmer winter low temperatures than the department’s previous map from 1990.
The new map divides the country into 13 zones arranged by minimum winter temperatures, in 10-degree increments. Among the shifts: The District and most of Virginia and Maryland are squarely in the relative balm of Zone 7. Specifically, they fall in the warmer half of Zone 7 where the mercury, on average, doesn’t go below 5 to 10 degrees Fahrenheit. Previously recorded in southeastern coastal Virginia, this zone now defines the coastal communities of the Chesapeake Bay and the Potomac River.
The colder Zone 6, which once embraced the Piedmont area and included much of Fairfax and Montgomery counties, is now pushed west of the Blue Ridge.
“The new map is generally one 5-degree Fahrenheit half zone warmer than the previous map throughout much of the United States,” said Kim Kaplan, of the Agricultural Research Service.
She said that in spite of the zone creep, the new map is not meant to validate climate change, and that the changes are driven in part by more sophisticated and fuller data collection. Using new technology, the map makers have been able to assess the effects of elevation, prevailing winds, bodies of water and urban heat islands in a way the old map could not, she said. Viewers can now type in their ZIP codes to get zone information.
Hardiness zones are used by gardeners, plant growers and breeders to match plants to their preferred growing climates. Officials said homeowners shouldn’t rip out plants that aren’t supposed to be growing in their zone.
“Even as sophisticated as this is, it’s only a guide. Nothing is better than the gardener’s knowledge of his own garden, what’s going to grow well there,” said the department’s chief scientist, Undersecretary Catherine Woteki, at a news conference at the National Arboretum.