Explaining Hardiness Zones.
 (Read 100+ times)
By Glory Lennon
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There you are at the garden center pondering what the tag on that wonderful little plant is trying to tell you. What the heck is a hardiness zone? Only zone you know of is the one your high school soccer coach tried to show you back in the day. Sorry, but this zone has nothing to do with sports. Knowing all the players on your favorite football team won’t help either. On the other hand geography can.
Not much good at geography? Better brush up on it if you’re going to start gardening. It’s rather important for the landscape. If you can find yourself on a map you’ve got half the work done. Next thing to do is take a look at a plant hardiness zone map usually found on the back of most seed packets, in good gardening reference books and almost all gardening magazines. As you will see the map shows the United States and Canada with colorful bands running across it in irregular shaped swatches. Each of these colors represents a different zone. They run from the coldest, Zone 1 up and around Alaska, the Arctic and most of Canada to the warmest Zone 11 in the tip of Florida, Hawaii and the Florida Keys.
The plant hardiness zone map was developed by the United States Department of Agriculture to help farmers in particular and gardeners in general assess the average minimum temperatures experienced during winter. Why is this important? To make it easier to choose plants which will survive the winters in your particular corner of the world or Zone. These temperatures vary, of course, from year to year when winters are more mild or far harsher than usual but they give a general idea of what is to be expected.
Average low temperature ranges expected in winter in each zone are as follows.
Zone 1- below -50 degrees F
Zone 2- -50 to -40 degrees F
Zone 3- -40 to -30 degrees F
Zone 4- -30 to -20 degrees F
Zone 5- -20 to -10 degrees F
Zone 6- -10 to 0 degrees F
Zone 7- 0 to 10 degrees F
Zone 8- 10 to 20 degrees F
Zone 9- 20 to 30 degrees F
Zone 10- 30 to 40 degrees F
Zone 11- Above 40 degrees F
At times you may see “a” or “b” following the Zone as in Zone 5a or Zone 6b. The “a” indicates a tiny bit warmer place than the rest of the Zone. The “b” indicates a slightly colder than usual spot within the range. This can be as little as 2-5 degrees difference.
There are factors which come to account for these little fluctuations within the temperature ranges such as proximity to large urban areas, large bodies of water and altitude. For instance almost all of North Carolina is in Zone 7, meaning its average low temperature can be from 0 to 10 degrees F. But on the coast, needless to say sea level, where the ocean tends to make the air moist due to evaporation and therefore warmer, it is in Zone 8, averaging 10 to 20 degrees F during winter.
Similarly, the higher up you are in altitude the colder it gets as in the mountains of northern Pennsylvania, a Zone 5, and Philadelphia, a large, sprawling urban area somewhat close to the ocean is in Zone 6. Within those mountains of Pennsylvania there are spots where two mountains meet or is particularly high up and consequently slightly colder. That is a Zone 5b. In a valley with extra protection all around it making it a bit warmer, such the valley city of Sugar Notch, is a Zone 5a.
Occasionally the Zone map can change due to several years of drought, more rain than usual or extra cold or extra warm weather. But in general things stay as they are and you can rely on the zone map to tell you what plants will survive your particular zone. For example the perennial flower Lupine is hardy in zones 4-8 which means it can tolerate low temperatures -40 to -30 degrees F. In Zone 8 however the Lupine tends to wilt in the super hot summers there unless situated in part shade.
On the other hand, there is the perennial Red Hot Poker supposedly hardy in zones 5-10 which means it can tolerate low temperatures -20 to -10 degrees F. But it didn’t make it through one particularly rough winter in my Zone 5b garden. That tiny bit of difference can be the death of a plant. We gardeners have to be extra generous with mulch for plants on the borderline of Zones. Or we can make tiny micro-climates in which to place our more delicate plants.
Either way the plant hardiness zone map does indeed come in handy when looking for plants which you can count on to survive your winter. Keep it handy, know your Zone and learn about making those micro-climates and you’ll have a garden which never fails.
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Author Bio Box: Glory Lennon
 Visit http://www.helium.com/user/32782 for more fascinating gardening lessons, amusing short stories and intriguing novel excerpts.
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