An important change took place in northern Ohio in mid-January, and there were no fireworks or parades. In fact, most of us did not know it had happened until weeks later.
The U.S.Department of Agriculture issued a revised Plant Hardiness Zone Map, or PHZM delineating the growing zones in this country. And so this final column in the alphabetical series, dealing with the letter Z, will celebrate the change of our zone from 5b to 6a.
The United States now is divided into 26 zones, determined by the average lowest annual temperature of the region, and our move is to a warmer designation. Where formerly our lowest average was between -10 and -15 degrees, it now has been determined to be a balmy -5 to -10.
Statistics were gathered over the period 1976 to 2005, and adjustments were made accordingly.
The temperatures as calculated are the average, with little weight given to the lowest temperatures experienced in each area.
To get a map and more information about the whole subject, you can go online to www.planthardiness.ars.usda.gov, where you will find a useful interactive map.
Janet Del Turco is a local gardener and a graduate of the Ohio State University Master Gardener program. Contact her at firstname.lastname@example.org.
Most of Ohio is included in Zone 6, with small pockets still rated 5b, mostly in Darke and Henry counties. There are additional microclimates throughout the state, where small hills and valleys or large areas of blacktop affect the temperature.
All gardeners are familiar with this, as our own gardens have spots where additional shelter or uninterrupted sun affects plant growth.
Since I read some months ago a change in the map would be forthcoming, I have been hoping the temperatures still would be calculated in Fahrenheit. Most of the world uses the Celcius scale.
When I am in England, I struggle with the weather forecast. A temperature of zero degrees sounds scary, but in our terms, that is 32 degrees Fahrenheit. The only way my mathematically challenged brain can convert the numbers is to remember 16C equals 61F (or more precisely 60.8), and just take a guess up or down from there.
There are many sites on the Internet with conversion tables that will do the work for you.
When Celcius was developed, calibrations were set at the temperatures of boiling water (100C) and freezing water (0).
The change in zones will not make much difference to the gardeners who pretty well know what grows in their area. It will cause some trouble and expense to nurseries and seed companies that print the maps on their seed catalogs and packets. I suppose that will translate into a few more pennies on seeds.
The excellent and informative catalog from Mulberry Creek Farm in Huron includes some helpful hints on determining winter hardiness. One is the presence or absence of good, well-draining soil in your garden.
Many plants will not grow well with wet roots.
The second factor is protection from winter winds. Planting near a windbreak of some kind will allow borderline plants to grow.
Then comes temperature in microclimates around the garden. A spot that is lower than the surrounding area or is sheltered from extremes by a wall or building may deflect cold winds and frosty conditions.
And finally, we are advised to leave most branches and leaves on perennials through the winter for added protection.
I have enjoyed collecting bits of information for these alphabetical columns. I am thinking that my next series, used when no immediate topic comes to mind, may be colors. So look for the white garden to appear in this spot one of these days.