What are "ZONES"? - Knowledgebase Question

Pittsburgh, PA
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Question by sgranberg
May 27, 1998
Just to let you know, I'm VERY new at this. I don't even have the house built yet, let alone a garden, but I'm learning. When I read comments in this and other garden sites, the respondants mention "zones". What are zones, and how do they pertain to Armstrong County, PA?

Answer from NGA
May 27, 1998
Zones are a useful thing to know about, you're right! They can help you select plants able to withstand the winter temperatures in your area. It is also almost a code between gardeners because it helps other gardeners relate to your local climate conditions.

The United States Department of Agriculture (USDA) developed a map showing average winter low temperatures across the country based on ten degree intervals or Zones. For example, USDA Zone 6 has winter lows between -10 and 0 degrees F, and USDA Zone 5 has winter lows between -20 and -10 degrees F. A conservative gardener in your area would always opt for plants rated hardy to zone 5 or colder.

The map gives you a good general reference guide to go by, but in your own garden, the winter weather and temperatures will also be affected by your local microclimate. This means for example, a sheltered spot in town will be more moderate than a windy, exposed spot in the country even if both are rated the same zone on the map. As a new gardener it wll also help you to ask experienced gardeners right in your neighborhood about the wind and precipitation patterns for your microclimate, too.

Most plants are rated with a minimum zone of cold hardiness. These are the numbers you see in catalogs or books: "hardy to zone 3", or sometimes simply, "zone 3". A plant rated hardy to zone 3 can withstand temperatures as low as 40 below zero!

In contrast, a plant rated to zone 8 will only tolerate lows of ten degrees above zero. Sometimes you will find a listing such as "zones 3 to 8" This means the plant is cold hardy all the way to zone 3 but does not do well in zones warmer than zone 8.

As a beginning gardener, you will find that the plants rated "zones 3 to 8" tend to be very reliable and dependable under a broad range of conditions. This may be a good overall group to start with until you gain a little more experience in your new location. In the meantime, keep reading, visit all the gardens you can, and keep asking questions!

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