Knowing what growing zone you live in allows you to select plants that tolerate expected temperature extremes and climate. Many environmental factors determine whether a plant survives and thrives in your landscape: soil type, soil acidity, available nutrients and moisture are all important conditions that affect plant growth. Although you can improve many of these conditions by watering, adding organic material and fertilizer, one critical growing variable outside of the owner’s control is temperature.
The United States Department of Agriculture focuses growing zone designations based on average annual minimal temperatures. Using latitude and longitude values, the USDA collected lowest temperatures recorded from over 14,000 stations located in Mexico, the United Statesand Canadabetween 1974 and 1986. The USDA color-coded hardiness map has 11 zones, with Zone 1 experiencing cold temperatures as low as -50 degrees Fahrenheit and Zone 11’s low temperatures remaining above 40 degrees Fahrenheit. The USDA further divides each zone into “A” and “B” groups reflecting a 5-degree difference in measured low temperatures. To find your USDA Hardiness Zone value, locate your area on the map and compare the color to the USDA Zone values. Most purchased plants and seeds have a USDA hardiness value or minimum tolerable temperature on their tags.
The western half of the United Stateshas complex gardening regions with variation in growing conditions based on elevation and precipitation in addition to latitude and longitude. Originally created for 13 western states by “Sunset Magazine,” the Sunset Zone Map divides the U.S.into 45 gardening areas based on the types of plants that grow successfully. To use the Sunset zone classification for your area, find your location on the Sunset Zone map and check the associated zone number. Each map contains information about the growing environment for that Sunset zone.
Determining which growing zone you live in is an important first step to planting the garden of your dreams.