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| Photo Credit: Courtesy of the USDA |
| This is the 2003 US National Arboretum’s “Web Version” of the USDA Plant Hardiness Zone Map. |
Hardiness zones remove some of the mystery of gardening by allowing a gardener to know at a glance whether a plant will survive winter cold in his or her part of the country. So they’re both empowering and budget-conscious, since these zones can help stop you from buying plants that won’t survive from year to year. If you’re not sure what these zones exactly mean, read on:
When you see “Zones 3-7” on a plant tag, what does it mean?This is the “hardiness zone,” developed by Harvard’s Arnold Arboretum in Massachusetts and the USDA, who put together guidelines to give gardeners an idea of how well their plants would survive the winter cold. The 1990 hardiness zone map was created based on historical weather patterns. The US has 11 zones, with lower numbers having colder winters. So Zone 3 is more typical of North Dakota, while Zone 9 is lovely Florida weather. Each hardiness zone differs by 10 degrees F, so the difference in low winter temperatures between zones 6 and 7 is 10 degrees; between zones 6 and 8, 20 degrees; between zones 6 and 9, 30 degrees, and so on. On the plant tag mentioned above, “zones 3-7” means that the plant will survive in those particular zones, or roughly from North Dakota to North Carolina. It’ll be killed by too much cold (most parts of Canada, for instance), and it won’t receive enough cold to survive if grown in Florida. Almost all plants have been assigned a hardiness zone. To find your zone, go to the USNA’s Website and click on your state. You’ll notice that each zone is divided into “a” and “b,” with “a” having slightly cooler winters than “b.” You should also note that being further north doesn’t always mean colder temperatures. For instance, Gainesville, FL; Portland, OR; and London, England, are all considered to be “Zone 8,” although they exist at 30-, 45- and 51-degrees latitude, respectively. This is because coastal winds and the jet stream modulate the weather in Portland and London. Large metropolitan areas are also slightly warmer, since their “asphalt jungles” retain heat.
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