How to Determine Frost Dates for Gardening Your Region

In gardening, frost dates refer to when the last spring frost occurs to when the first fall frost begins. The gardening season begins each spring as frosty nights ease up and plants send out tender new shoots. Spring and summer bring an eruption of growth, flowering, and fruiting. With the arrival of fall and winter, plant growth slows to a stop as nights get cold and frost forms on the ground.

Knowing frost dates allows you to plant vegetables at the proper time to ensure that they flourish. You can plant cool-season crops as soon as frost is no longer expected in spring; these plants often fade and may die altogether during the heat of summer. A second window for planting cool-season crops opens up in late summer and early fall; once mature, these species can actually survive a light frost (in mild climates, they may even continue producing into the winter months). Warm-season crops are typically planted about six weeks after the last frost, thriving through the summer months and finally turning brown with the first frost in fall.

Every environment has its own microclimates, which is why it is necessary to understand the frost dates in your area. There are many ways to determine your area’s first and last frost date.

1. 1. Online calculators and charts: Many seed and garden websites provide the average date of the first and last frost in your area. To look yours up, enter your zip code into an online calculator to determine the chance of frost and average frost dates. Your local weather station likely provides its own chart as well.
2. 2. USDA hardiness zone map: The USDA maintains a plant hardiness map that divides the country into 13 zones based on average annual minimum temperature. Find your zone and familiarize yourself with the fruits, vegetables, flowers, and herbs that thrive in it. The USDA map provides critical information for growing both perennials and annuals.
3. 3. NOAA national climate report: The National Oceanic and Atmospheric Administration’s National Centers for Environmental Information includes freeze dates in its annual climate reporting. Referring to the previous year's last and first frost date can help you estimate when to expect the current year's growing season.
4. 4. Gardening centers: When you go to a garden center or browse online nurseries, you’ll find that plants are often labeled with a number corresponding to a hardiness map that tells you whether the crop you’re considering will survive in your zone. Sometimes you will find a range of cold hardiness zones on the label (zones 4 through 8, for example), indicating both lower and upper climatic thresholds.
5. 5. Seed packets: You’ll notice that seed packets typically indicate the number of “days to maturity” that the crop requires. Knowing this information, count backward from your area’s average date of last frost to determine the latest possible date to plant each crop. But keep in mind that sometimes crops grow more slowly than expected and that frosts can come earlier than usual—it’s wise to add two to four weeks, just to be safe. You can start seeds indoors to extend the growing season.

Once you’ve determined your number of frost-free days per year—the length of your growing season—you’ll have a much better idea of what to plant and when to plant it.

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