Average Frost Dates
A “frost” date really means when temperatures fall to 32°F or lower, which is cold enough to damage leaves or kill young, tender plants. In the most basic sense, your “growing season” is essentially the time between when the last freeze happens in spring and the first time temps get to freezing later in the year, known as the first fall frost date. Those events don’t happen on the exact same days each year, of course, but you can get a pretty good idea of the timeframe based on when they have occurred in the past. To figure out when you’ll likely see the last of ice this winter, take a glance at the map above. It’s compiled from 30 years of weather data collected by NOAA National Centers for Environmental Information. For example, if you live in Southern Illinois, you’ll probably be able to plant outside during the first part of April, but if you’re farther north in Illinois, you should wait till the second half of the month to be safe. You can also get the map information personalized for your zip code through the National Gardening Association’s online database. By using these guidelines, you’ll have a window for planting outside. However, spring weather can often shift quickly, so make your local weather forecasters your BFFs. They’ll warn you about any sudden temperature drops coming your way. If that happens, make sure to bring in any tender plants in containers or cover newly planted veggies or annuals with an old cotton sheet until the weather warms again.
What You Can Plant Outside Before the Last Frost Date
Your heat-loving tomato seedlings will definitely have to wait for warmer weather, but you can go ahead and start growing cool-season vegetables and flowers. These unsung heroes of the garden are cold-hardy crops that you can grow as the temperatures are still chilly (and even a little frosty) in spring. You can even replant them again in late summer for fall color and harvests. As long as your soil has thawed out enough to dig in, you can sow most cool-season vegetables right in the garden rather than starting them indoors first. These include leafy greens like Swiss chard, kale, and spinach. Radishes also grow quickly in spring and tolerate frost well. Certain annual flowers like pansies and snapdragons that often appear at garden centers very early in the spring also can take mild freezing temperatures and keep on blooming. Bare-root trees (especially fruit trees hardy in your area) can also be planted before your last frost date—because they haven’t started to actively grow new leaves yet, they won’t be harmed by a little below-freezing weather.
