What You Need to Know About Your First Fall Frost Date
If you live where frost occurs, that first icy autumn day can wreak havoc on your garden. Knowing your area's average first fall frost date can help you minimize damage to your plants and help you prepare for the colder months ahead.
In our gardens, we're usually trying to enjoy all our gorgeous annuals, tropical plants, veggies, and herbs outdoors for as long as possible before the first fall frost happens. But once air temperatures drop to 36°F or below, the leaves of these plants will wither and blacken, bringing your garden party to a halt. Exactly when that might occur varies from year to year and from region to region, but finding out your average first fall frost date will help you know when to expect things to get cold enough to damage or kill your plants. That way, you can make plans to bring frost-sensitive plants indoors and clean up your garden for the winter. Luckily there are several resources to help you figure out when to do that.
First Freeze Map and Average Frost Dates
To get started, find where you live on the map above. It shows six different time periods, each spanning about a month from the end of June to the end of December. Each of these is color-coded to the regions where the first frost can happen during that range of dates. For example, if you live in Ohio, you may get your first fall frost sometime between September 30 and October 30.
If you'd like to narrow down your window of time a bit more, we like this handy online tool created by the National Gardening Association for quickly looking up first frost dates by zip code. It uses weather data from the National Centers for Environmental Information but packages it so you see just the numbers that apply to your area.
Find Your USDA Plant Hardiness Zone
Another helpful resource is the USDA Plant Hardiness Zone Map. It shows how cold your region can get in the winter. You can search by zip code or your state to find your USDA Zone. Your Zone number can help you know which plants will be hardy in your area and likely to survive your winter weather, including your first fall frost. The current version of the USDA map was created in 2012 and is the latest in a long line of maps showing averages of the coldest winter temperatures.
Your yard—or a spot in it—may experience frost well before others in your neighborhood. This is because of microclimates caused by factors like elevation that affect air temperatures near the ground. If you live at the bottom of a hill, slope, or valley, the cold air will flow down to you, making your property colder than the surrounding ones, and your first frost will happen earlier. Likewise, a sheltered spot may not have frost until several weeks after other areas. Keep this in mind when a light frost is predicted—your garden just might get by unscathed until temperatures drop even more.
Plants That Won't Survive a First Fall Frost
Most annuals and tender perennials die off when Jack Frost comes around. If it's only a light frost, sometimes you can keep your geraniums or bedding plants going a bit longer if you cover them overnight with an old sheet or towel. Uncover them when temperatures rise the next day. This goes for your pots of fall mums, too, which can take a light frost but not a hard freeze.
Check the tags of any plants you're growing in containers. Those listed as USDA Zones 9 to 14, such as coleuses, elephant ears, and begonias, can be brought into a garage or shed before a light frost. When the weather warms up again, you can move them back outside to enjoy a little longer.
If you like to move your houseplants like philodendrons and tropical ferns outside for the summer, know that they will be damaged when night temperatures cool to 45°F–50°F. If you want to keep them going, bring them indoors well before the first frost.
Many herbs and summer vegetables won't tolerate much frost. So harvest those remaining tomatoes (even the green ones); cut bouquets of dahlias, zinnias, and marigolds; make pesto with the last of your basil; pickle the cucumbers; or pick a pint of peppers when a cold snap is coming. Then say goodbye to your summer garden friends, cut down the plants, and put them on the compost pile. It’s much more pleasant to do the cutting before a freeze turns these plants black and slimy. You can leave cool-season crops like lettuce and potatoes a little longer, but harvest the produce before heavy frost at 28°F or lower damages them.