Gardening Basics For Dummies. Steven A. Frowine

that gardeners in North America use, but others exist. The American Horticultural Society’s Heat-Zone Map is more useful and popular for people in the Southern and Western United States, while Sunset’s Garden Climate Zones Map, though complex, serves the Western states well. Furthermore, Canada also has its own hardiness map (see the Color Insert).

      Looking at the world’s plant hardiness zone maps

      Every part of the world has its own hardiness zones, and most maps are set up the same way. The USDA Plant Hardiness Zone Map, for example, is a color-coded or shaded map, sometimes accompanied by a chart that expresses the same information. Check out the Color Insert to see this map; you can also see the map (and others) in many places after you become tuned in to it — a poster tacked up on the wall at your local garden center, the back flyleaf of gardening books, in the back pages of most garden magazines, tucked into the interior of your favorite gardening catalog, or online. The map is interactive so you can find your zone by entering your Zip code. You can check this map out at the National Gardening Association NGA) website at https://garden.org/nga/zipzone/ or other online versions of the map, often found on the websites of mail-order seed companies and plant nurseries, which usually are interactive.

The United States Department of Agriculture published, and has occasionally modified and updated, this hardiness zone map of North America. The most recent map, based on climate data gathered at National Weather Service stations throughout the United States and by weather stations throughout Canada and Mexico, came out in 1990 and was updated in 2012. You can find 11 zones marking the average lowest winter temperatures, with Zones 2–10 divided into subzones.

      Canada’s plant hardiness zone map, suited for Canada’s colder climate, shows nine zones, based on average climatic conditions and altitude of each area. The harshest zone is 0, and the mildest is 8. In addition, the major zones are further divided into subzones. For example, Zone 4 splits into 4a and 4b, where zone a is slightly colder than zone b. You can see Canada’s map in the Color Insert or online at http://planthardiness.gc.ca/.

      Here are a few other hardiness zone maps that may interest you:

       Europe: The Hardiness Zone Map of Europe presents a general overview of the European continent and can be broken down further into each European nation and the zones within it. You can see this map online at www.gardenia.net/guide/european-hardiness-zones. The Royal Horticultural Society (RHS) offers plant hardiness information for United Kingdom. Check this out on their website at www.rhs.org.uk.

       China: China’s plant hardiness zone map covers arguably largest and most varied gardening spots in the world. You can view it at www.backyardgardener.com/zone/china.

       Australia: The Australian government has established a series of maps that many Australian gardeners use to gauge not only planting zones and climates but also rainfall. To view the plant hardiness zone map of Australia, go to www.anbg.gov.au/gardens/research/hort.research/zones.html.

      You can find zone maps for South America and Africa online as well.

      WHO ARE THE ZONE WIZARDS?

      Exactly who determines what plants are appropriate for what zones? Well, the standard response is horticultural and climatological experts, whoever they are. Even though these climate maps are helpful, you have to think about them as purely a guideline. Gardeners have always been known to test the limits and try something that isn’t supposed to grow where they live. And why not? You may prove the experts wrong.

Traveler beware: If you buy a plant marked as perennial or hardy in the deep Southern United States or California and you live in a chilly northern region, the plant may be labeled such only for the area where it’s sold.

      Warming up to the heat-zone map

      The USDA map, although enormously popular and widely used, has its limitations. For example, Zone 7 in Maryland is a world away from Zone 7 in Oregon, or north Texas, or the foothills of California’s Sierra Nevada mountains. In many parts of the country, heat rather than cold dictates which plants are able to survive from one year to the next.

      Thus, in 1997 (after years of study and research), the American Horticultural Society released its own map, the AHS Heat-Zone Map. This has proven quite useful to gardeners in the South and West. You can search online for this map or it is available http://solanomg.ucanr.edu/files/245158.pdf.

      The AHS map has 12 zones. Relatively cooler Zone 1 is defined as having only one day of 86°F weather per year; sweltering Zone 12 has 210 days of such heat or more.

      Research has shown that 86°F (30°C) is the temperature at which many plants — that is, their cells, or plant tissue — start to experience damage from heat. That’s why that point became the baseline for laying out the heat zones.

      U.S. gardeners in areas where the main source of plant stress isn’t winter cold but summer heat prefer this system. Nurseries in hot areas are starting to refer to these zones more and more. If the heat-zone information isn’t supplied for a plant you’re interested in, look in newer regional reference books and plant catalogs and websites.

      Savoring the Sunset zones

      In the Western United States — a region loosely defined as the states of Arizona, Utah, New Mexico, California, Nevada, Idaho, Montana, Wyoming, Colorado, Oregon, and Washington — neither the USDA Zone Map nor the AHS Zone Map gives complete enough information. Complex and varied terrain and dramatic weather variations conspire to make this particular region unique.

      The Sunset Publishing Company, based in the San Francisco area, devised its own Garden Climate Zone Map, which you can find online at www.sunset.com. Just search the site for Sunset Climate Zones. You may also see it in many publications, from books to subscriber-driven magazines to newsstand issues. Gardeners, landscapers, and nurseries in the West often refer to these Sunset zones.

Sunset’s zone map contains 45 zones. Yep, 45. These zones actually cover the entire United States, Southern Canada, and Northern Mexico, and they’re all very individualized and specific. For example, Sunset Zone 3 is defined as West’s Mildest High-elevation and Interior Regions and covers much of the area east of the Cascades in the Northwest, where residents see snow cover in winters but also blazing summers. Zone 16 is Northern and Central California Coast Range Thermal Belts, from Santa Barbara County to Marin County; this area gets drying summer winds, fog, and a climate made mild by proximity to the ocean.

      These Sunset zones can particularly empower a new or frustrated Western U.S. gardener, especially if the source of plants also uses the same zones. So ask at the local nursery or garden center — realizing, of course, that nobody stays in business for long by selling plants that don’t thrive. Or go out and buy Sunset publications tailored to your particular zone and do some reading and research; then go shopping near or far when you know just what you want.

      Reading plant hardiness zone maps

      Take a look at the USDA Plant Hardiness Zone Map, either in the color section of this book or online by searching for it. It’s available on many different garden sites. Notice that Zone 1, located at the top or northernmost part of the map, is