Gardeners in northeast Ohio were shaken up a bit last week by the news that our area jumped an entire zone according to the U.S. Department of Agriculture.
But just because the USDA said we are now a zone warmer doesn't mean our gardens have changed overnight.
For those who aren't familiar with the USDA Plant Hardiness Zone Map, let me explain a bit.
Back in the 1920s and 1930s, someone got the bright idea that measuring which plants will survive in various regions of the country could be determined by the coldest temperatures in those regions. These bright people divided the country into sections assigned numbers, with 1 as the coldest and 10 as the warmest. Ranging from zone 1 in northern Canada and Alaska to zone 10 in southern Florida, northeast Ohio was given the distinction of being in zone 5.
The first printed zone map came out around 1960 and was updated in 1965 with even more accurate temperature information. By 1990, better forms of measuring temperatures enabled the map to calculate zones once again, this time dividing them into sub-sections such as 5a and 5b, 6a and 6b, you get the idea. We were 5a, the coldest of the zone 5 division.
To coordinate with the zone map, commercial growers labeled plants and seed packets for retail sale with the zones where those particular plants would grow. Consumers would have better gardening experiences and fewer plant deaths if we bought plants labeled zone 5 or lower and gave them the proper growing conditions.
And then we have the rebels. These are gardeners who are so confident with their green thumbs, they will defy the zone map and plant zone 6 plants in their zone 5 landscape.
''My Hydrangea macrophylla blooms every summer,'' these cocky gardeners might say. ''I don't know why you have so much trouble with yours.''
Of course, plants not only don't read labels, but even in our own backyards, we have pockets of temperature differences called microclimates. We can usually tell where they are by how well our plants grow. These areas are determined by how well protected they are from harsh winter winds or the freezing and thawing of the soil. Our winter also makes a difference. Snow can act as an insulator against the coldest of temperatures. If we have cold temperatures but no snow to blanket the plants, we may notice some plant loss in the spring that we weren't expecting because we thought we had a mild winter.
On June 25, the USDA made the announcement that the zone map had changed once again, but this time the changes indicated we could very well be warmer than we were 80 years ago. Without pinning themselves down to admitting global warming, the USDA website explained the changes were the result of more efficient technology using highly sophisticated algorithms that interpreted local weather station data and geographic characteristics. One their website, the USDA incorporates a digital Geographic Information System or GIS to provide an interactive map where we can put in our zip code and get the zone we are in, just in case we might be in one of those little pockets that might change our area due to elevation and proximity to bodies of water and terrain.
Many gardeners are meeting these new changes with a lot of skepticism, while others are so excited they are revamping their spring plant orders to include plants that were formerly written off as too tender for our winters.
My advice is to not jump in with both feet too quickly. If that Nikko Blue hydrangea you were gifted a few years ago and planted in your yard happily blooms every year, you can probably grow other zone 6 plants there as well. But if the buds that formed on last year's stalks still die from winter winds, you may want to reconsider spending too much of your plant budget experimenting with tender perennials.