In 1965, the U.S. Department of Agriculture created the Plant Hardiness Zone Map, which placed our area in Zone 5B.

The “5” indicated a low temperature range from -15 to -10 degrees. The “B” indicated the warmer section of Zone 5 while “A” indicated the colder section.

Now, however, the USDA has placed us in Zone 6B. This indicates a low temperature range from -5 to 0 degrees. Did this occur as a result of global warming or something else?

The ARS (Agricultural Research Service), which is the in-house research arm of the USDA, says that it is new technology that makes the map more accurate and not global warming.

The last version of the map had 13 years of data while the new map has more than 30 years of data collected from more weather stations and locations.

The enhanced data also looks at closeness to water, elevation changes, prevailing winds, and land slope.

Two new zones, 12 and 13 (we used to have 11) were added to more properly classify tropical plants.

What does this mean to us gardeners?

It’s almost the official go-ahead to try and grow plants that we may have thought were off limits.

However, for some of us, we were growing Zone 6 plants before we got the official go ahead. Warmer spots in your yard can be obtained by planting against a stone or brick wall, which lets plants take advantage of the radiating heat while a thick layer of mulch protects the roots of tender plants.

I’ve grown several Zone 6 plants that were not against a wall but were mulched only by fallen maple leaves.

What are some Zone 6 plants that you might want to try — Western Spice Bush, Muhly Grass, Variegated Boxwood ‘Elegantissima,’ Sweetspire ‘Merlot,’ Crocosmia ‘Lucifer’ or “Star of the East,’ Japanese Snowbell, Southern Magnolia, Crape Myrtle (hardiest selections) and there are many more.

I’ve been growing Hydrangea ‘Blue Billow’ (Zone 6B) ever since I saw it at Riverside Gardens in Youngstown, Ohio, and it bloomed the first year and continues to do well.

It’s mulched but not in a protected area, so I guess it knew the change from Zone 5 to 6 was coming.

Who knows? Someday we may be trying Zone 7 plants, but don’t be afraid to try plants that are in Zone 6 because we’re certainly there now.

Maryellen Walter is a Penn State Butler County Master Gardener.