You’ve probably seen plant labels, seed packets, online information, and comments in gardening books about hardiness zones, but what are these zones, and how can they help you in the garden?
Being unable to head to warmer weather each winter, under an umbrella in the peak of summer, or in search of more food or better conditions, plants are stuck where they are. All plants have basic needs that must be met wherever they end up growing:
If they are planted in the right location, they can grow and thrive. Remove any of those favorable conditions and life can get downright difficult. The most important factor to a plant’s health is temperature. Choosing plants suited to your local climate can make all the difference in whether or not they thrive or die. The USDA Hardiness Zone map can help.
History of the Hardiness Zone map
In an effort to help farmers and gardeners select the best plants for a particular geographic area, the U.S. Department of Agriculture came up with the Hardiness Zone map in 1960. This map was revised in 1965, 1990, and 2012. These revisions are due to more accurate measurements and expanding heat islands (cities, roads, and urban development). The most recent version is based on temperatures collected from 1976 through 2005. In this version, two new zones were added.
How to use the USDA Hardiness Zone map
The 2012 Hardiness Zone map is available online. All you have to do is enter your zip code. Under the search field, you will see your zone. You can also look at a static state map that has more detail. My zone, living in the south Bay Area, is 9b, which means the local average winter minimum temperature is 25 to 30°F. But, because I know my yard, I know that those temperatures are not entirely accurate. For more reasons than I know, my yard has a microclimate that is always a little warmer than local weather reports suggest. This means I can provide plants with slightly warmer winter temperatures. It also means that I must provide more irrigation and better sunburn protection through the summer.
Try hanging a thermometer somewhere in your garden to fine tune the information you get from the USDA Hardiness Zone map.
You can grow a surprising amount of food in your own yard. Ask me how!