Illinois Planting Zones

The Prairie State encompasses five distinct USDA hardiness zones—5a, 5b, 6a, 6b, and 7a—creating a fascinating gradient of growing conditions. 


From the wind-swept shores of Lake Michigan to the fertile river valleys of southern Illinois, the state's rich black prairie soils have earned it recognition as one of America's most productive agricultural regions.


In this comprehensive guide, you'll discover:

The state's position between the Great Lakes and the Mississippi River valley creates unique growing opportunities. When properly timed, both cool-season crops and warm-season vegetables can thrive. 

Image from USDA

Characteristics of Illinois's Planting Region

Illinois has a continental climate characterized by distinct seasonal changes, with significant temperature variations between summer and winter. The state's north-south orientation creates notable differences in growing conditions between regions.

As an Illinois gardener, you can expect:

  • Hot summers with July temperatures averaging 75°F to 85°F (23.9°C to 29.4°C)
  • Cold winters, especially in the north, with January averages ranging from 14°F to 32°F (-10°C to 0°C)
  • Annual rainfall averaging 35-45 inches, increasing from north to south
  • Lake effect influence in northeastern regions
  • Approximately 150-190 frost-free days, depending on location

The Illinois growing season varies significantly by region:

  • Northern Illinois: Late April to early October
  • Central Illinois: Mid-April to mid-October
  • Southern Illinois: Early April to late October

Challenges of Growing in Illinois

Extreme Temperature Fluctuations 

Spring weather can be particularly unpredictable, with sudden temperature swings that can damage early plantings. Late frost in spring and early frost in fall can shorten the growing season.

Wind Exposure 

The prairie landscape offers little natural wind protection, which can damage plants and increase water evaporation rates. Chicago's famous winds can be particularly challenging for gardeners.

Soil Variations 

While much of Illinois boasts rich prairie soils, urban areas often have poor, compacted soil, and northern regions may have heavy clay. Southern Illinois can have more acidic soils requiring amendment.

The Benefits of Using a Greenhouse in Illinois

For Illinois gardeners, a greenhouse isn't just a luxury—it's a game-changing tool that transforms a limited growing season into year-round gardening opportunities. 

Here's how protected growing space can revolutionize your Illinois garden:

1. Extend Your Growing Season 

  • Without a Greenhouse: In central Illinois, the typical outdoor growing season runs from early May to late September. This shorter season limits the variety and volume of crops you can enjoy fresh.
  • With a Greenhouse: Start planting as early as March and continue harvesting into November. With the extended season, you could be enjoying fresh tomatoes for your Thanksgiving dinner!

Learn more about your area's specific growing dates and the best vegetables to plant in each part of Illinois.

Customer images of their Greenhouse setup in Illinois

2. Grow a Wider Variety of Vegetables Without a Greenhouse: 

  • Without a Greenhouse:  

Illinois outdoor gardens thrive with:

  • Tomatoes
  • Peppers
  • Corn
  • Potatoes
  • Squash
  • Melons
  • Okra
  • Green beans
  • With a Greenhouse: 

A controlled environment allows for a broader selection of plants, especially those that need warmer temperatures or a longer growing season, including:

  • Lettuce
  • Spinach
  • Kale
  • Arugula
  • Swiss chard
  • Broccoli
  • Cauliflower
  • Peas
  • Brussels sprouts
  • Cabbage
  • Carrots
  • Radishes
  • Beets
  • Turnips
  • Celery
  • Cucumber
  • Bell peppers
  • Eggplant
  • Figs
  • Green beans
  • Asparagus
  • Artichokes
  • Kohlrabi
  • Melons

Why Planta Greenhouses?

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