Gardening Articles: Flowers :: Perennials
A Gardener's Guide to Zone Maps (page 4 of 4)
by Joseph F. Williamson with NG
The National Gardening Zone Map
The 12 regions of the National Gardening Zone Map descend directly from the Koppen-type map that organizes regions of similiar native vegetation. It's usefulness comes into play when the zones are correlated to the USDA, average minimum-temperature zones. When a plant or activity is recommended for a particular region and zone within that region, the gardener has significantly more assurance of success compared to advice for the USDA Zone alone. For this reason primarily, this approach has within the past year become the most popular Internet-based zone system.
An example to illustrate the point is the Baily acacia tree (Acacia baileyana). A current reference books recommends it for USDA Zones 8 through 11, suggesting that it is appropriate for a gardeners in Savannah on the east coast through San Diego in the west. But it's not. If on the other hand you can recommend the plant for zones 8 through 11 in the Southwestern Deserts, Southern and Northern California, it works.
Know Your Maps
Although no single map can answer every question about plant adaptability, each one has some merit, often compensating for the weakness of another. In the near future, most home gardeners in the western United States may continue to rely on the Sunset zone map. Gardeners east of the Rocky Mountains will likely continue with the USDA Zone Map and the National Gardening Zone Map, and gardeners throughout the Sunbelt will appreciate the AHS Heat Zone map. Garden designers and others planning permanent landscapes will probably use all kinds.
Joseph F. Williamson is the former garden editor of Sunset magazine, and a key architect of Sunset's gardening zones.
Illustrations USDA and National Gardening Association