What Is a Frost Date?

A frost date refers to when temperatures fall to 32°F or lower, which is cold enough to damage leaves or kill young, tender plants.

The growing season is essentially the period between the last freeze in spring (the last frost date) and the first time temperatures reach freezing later in the year (the first frost date). These dates vary from year to year and also differ by location.

The last frost date can vary significantly between regions. For example, areas in Southern Illinois may be able to plant outdoors during the first part of April, while areas farther north may need to wait until the second half of the month.

Frost-date guidelines provide a general window for planting outdoors. However, spring weather can change quickly, so it is important to monitor local weather forecasts for sudden temperature drops.

If a cold snap is expected, bring tender container plants indoors or cover newly planted vegetables and annual flowers with an old cotton sheet until temperatures rise again.

What to Plant Outside Before the Last Frost Date

Heat-loving tomato seedlings should wait for warmer weather, but cool-season vegetables and flowers can be planted before the last frost date.

Cold-hardy crops can grow while temperatures are still chilly and can tolerate light frost. They can also be planted again in late summer for fall color and harvests.

Once the soil has thawed enough to dig, many cool-season vegetables can be sown directly in the garden instead of being started indoors. These include:

• Swiss chard
• Kale
• Spinach
• Radishes

Radishes grow quickly in spring and tolerate frost well.

Certain annual flowers can also tolerate mild freezing temperatures before the last frost date. Examples include:

• Pansies
• Snapdragons

Bare-root trees, especially fruit trees that are hardy in the local area, can also be planted before the last frost date. Because they have not yet started producing new leaves, they are less likely to be harmed by a short period of below-freezing temperatures.

Avoid planting tender seedlings or young plants too early just because there are a few warm days in early spring. Knowing your area's last frost date and monitoring the weather can help protect plants from sudden cold snaps.