When to Plant in Illinois

Illinois stretches about 400 miles north to south. Chicago-area gardeners face later last frost dates than those in southern Illinois near Cairo, often by a full month. Southern Illinois warms up significantly earlier.

The state's prairie soils are among the richest in the world, which is great news for vegetable gardeners. Most of Illinois has deep, fertile soil that produces excellent crops with minimal amendments.

Common Mistakes

Planting too early in Chicagoland — Lake Michigan creates unpredictable spring weather patterns.
Not accounting for the north-south climate difference — southern IL can plant weeks earlier.
Skipping windbreaks — Illinois winds can dry out soil and stress young transplants.
Ignoring the excellent fall growing conditions — cool autumn weather extends the harvest season.

FAQ

What is the last frost date?

The last frost date is the typical date in spring when your area has its final frost. After this date, it's generally safe to plant warm-season crops outdoors.

When should I start tomatoes indoors in Illinois?

Start tomato seeds indoors about 6–8 weeks before your last frost date. In the Chicago area, that's usually late March. In southern Illinois, you can start in early March.

Can I plant before the last frost?

Yes — cool-season crops like lettuce, peas, spinach, and broccoli can handle light frost and should be planted 4–6 weeks before your last frost date.

Why does timing vary so much within Illinois?

The 400-mile north-to-south span means southern Illinois has a much longer season than the Chicago area. Lake Michigan also affects spring temperatures in the northeast.

What if I live in a frost-free area?

Illinois doesn't have frost-free areas, but southern Illinois near the Ohio River has a significantly longer growing season. Enter your zip code for exact frost dates.

How does Plan My Garden create my schedule?

You enter your zip code, and we look up your local frost dates. Then based on the crops you pick, we calculate when to start seeds, transplant, and harvest — personalized to your location.