Know Your Zone!

Why are plant hardiness zones so important for gardening? Plant hardiness zones are based on lowest annual temperatures for a region, and help gardeners determine which perennial plants are likely to survive the winter. If you’ve noticed your hardiness zone recently changed, that’s because the zones are based on the average lowest temperatures over a 30-year period. In the past thirty years in Chicagoland, we’ve experienced more extreme temperature fluctuations than in years past. Plant hardiness zones are also tied to first and last frost dates for a given area. Although much of the area surrounding Chicago is zone 5, the city is considered to be zone 6 – likely because of the temperature-stabilizing effect of Lake Michigan. First and last frost dates are especially important for gardeners in determining when to set out or bring in/cut back annual plants. Although we typically think of our last frost-free date in Chicago as around Mother’s Day and the first frost date as around Halloween, this can vary by 2-3 weeks in a given year. To determine your plant hardiness zone, check out this web site. Be sure to enter your zip code for the most accurate hardiness zone – don’t go by the visuals on the map alone! http://planthardiness.ars.usda.gov/PHZMWeb/ Wondering where to find information on the first and last frost dates? Get comfortable with your favorite website for local weather and check nighttime low temperatures in the spring and fall. To know what you’re looking for, here’s an explanation of frost and freezes: The first frosts of fall are usually very light – somewhere between 35 and 32 degrees Fahrenheit. Many plants in the fall garden can usually survive a light frost, as they have been acclimating to cooler temperatures throughout the fall. A light freeze is...

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