When To Plant Corn In Illinois

Knowing when to plant corn in Illinois is the single most important factor for a successful harvest. Getting your timing right means stronger plants and better yields, and this guide will help you hit that perfect window.

Illinois is a top corn-producing state for good reason. Its climate and deep soils are ideal. But the weather here can be tricky, with late frosts and wet springs. Planting too early or too late can lead to poor germination, weak stalks, and disappointing ears.

The short answer is that corn planting time in Illinois typically runs from mid-April through mid-May. However, the ideal date shifts depending on where you live in the state. Soil temperature is your best guide, not just the calendar.

Key Factors for Determining Your Planting Date

Three things matter most: soil temperature, frost risk, and your region. Let’s break each one down.

1. Soil Temperature is Critical

Corn seeds need warm soil to germinate properly. The magic number is 50°F (10°C). You should aim for a consistent soil temperature at planting depth.

Use a soil thermometer. Check at a 2-inch depth in the morning for an accurate reading.
Plant when soils are consistently at or above 50°F. 55°F to 60°F is even better for strong, quick emergence.
Cold, wet soils below 50°F can cause seeds to rot or lead to seedling diseases.

2. The Last Frost Date

While corn seedlings can tolerate a light chill, a hard freeze will kill them. You need to know your area’s average last spring frost date.

Northern Illinois: Last frost around May 10-15. Planting often begins in early to mid-May.
Central Illinois: Last frost around April 20-30. Planting often begins in late April.
Southern Illinois: Last frost around April 10-20. Planting can often begin in mid-April.

It’s generally safe to plant 1-2 weeks before the average last frost if soils are warm enough, as corn takes about 1-2 weeks to emerge.

3. Illinois Regional Planting Windows

Here’s a more detailed look at the typical optimal windows across the state. These are guidelines that assume good soil conditions.

Northern Illinois (Zones 5a-5b): Optimal planting is May 1 to May 20. Wait for soils to warm up fully here.
Central Illinois (Zones 5b-6a): Optimal planting is April 20 to May 10. This is the heart of the Corn Belt.
Southern Illinois (Zones 6a-7a): Optimal planting is April 10 to April 30. This region gets a head start.

Step-by-Step Planting Guide for Illinois Gardeners

Follow these steps to get your corn off to the best possible start.

Step 1: Prepare Your Soil

Corn is a heavy feeder. It needs rich, well-drained soil.

Test your soil in the fall or early spring. Corn prefers a pH between 6.0 and 6.8.
Add compost or well-rotted manure a few weeks before planting. This improves fertility and drainage.
Consider tilling or turning the soil to loosen it, especially if its compacted from winter.

Step 2: Choose Your Corn Variety

Select a variety suited for Illinois. Check the “days to maturity” on the seed packet.

Early Season (70-80 days): Good for northern IL or if you plant late.
Mid-Season (80-90 days): A reliable choice for most of the state.
Full Season (90-100+ days): Best for southern IL or early planters in central regions wanting maximum yield.

Step 3: Planting Your Seeds Correctly

Proper depth and spacing makes all the difference.

Plant seeds 1.5 to 2 inches deep. In sandy or drier soils, plant a little deeper, up to 2.5 inches.
Space seeds 8 to 12 inches apart within a row.
Space rows 30 to 36 inches apart. This gives plants room and allows for pollination.
Water the rows thoroughly after planting to ensure good seed-to-soil contact.

Step 4: Plan for Pollination

Corn is wind-pollinated. For a good harvest, you must plant in blocks, not single long rows.

Plant at least 4 rows side-by-side. This helps the pollen from the tassels reach the silks on the ears.
A small square block is more effective than one or two long rows.

What Happens if You Plant Too Early or Too Late?

Missing the window has consequences.

Risks of Early Planting

Seed Rot: Cold, damp soil causes seeds to decay before they sprout.
Slow Emergence: Seeds sit dormant, vulnerable to insects and fungi.
Frost Damage: A late frost can wipe out young seedlings, forcing a replant.

Risks of Late Planting

Reduced Yield: Plants may have less time to develop full ears before fall frost.
Heat Stress: Late-silking corn can hit peak summer heat, hurting pollination.
Insect & Disease Pressure: Later plants often face more issues from pests like corn borers.

Tips for a Bountiful Illinois Corn Harvest

A little extra care during the season pays off big.

Watering Wisely

Corn needs about 1 inch of water per week. The most critical period is during tasseling and silking, when the ears are forming. If it’s dry, deep watering is essential then.

Fertilizing for Growth

Corn uses a lot of nitrogen. Side-dress with a nitrogen-rich fertilizer when plants are about knee-high (12 inches tall). This gives them a boost for stalk and ear development.

Weed Control

Keep weeds down, especially early on. They compete for water and nutrients. Mulching around plants can help suppress weeds and retain soil moisture.

FAQs: Planting Corn in Illinois

Can I plant corn in June in Illinois?

Yes, but it’s not ideal. Early June planting of short-season varieties can work, especially in central and southern Illinois. Yields will likely be lower, and the crop faces more summer stress. It’s a gamble if an early fall frost arrives.

How long does it take for corn to grow?

From planting to harvest, it typically takes 70 to 100 days, depending on the variety you choose and the summer weather conditions. Always check the “days to maturity” on your seed packet.

What is the best corn to grow in Illinois?

Mid-season varieties (80-90 day maturity) are the most reliable for across the state. Popular types include sugary enhanced (SE) and supersweet (SH2) varieties for home gardeners. Heirloom varieties like ‘Golden Bantam’ also do well.

Can I plant corn after a rain?

Be careful. Wait until the soil is workable, not muddy. Planting in wet, clumpy soil can lead to compaction around the seeds and poor root growth. Let the soil dry out a bit first.

What do I do if a late frost is forcasted after I plant?

If corn seedlings have just emerged, you can cover them overnight with row covers, cardboard, or even plastic buckets to protect them from a light frost. Remove the covers in the morning.

Timing your corn planting in Illinois is a blend of science, observation, and a bit of local know-how. By focusing on soil temperature, your regional window, and good planting practices, you set the stage for a healthy and productive crop. Keep an eye on the forcast, get your soil thermometer ready, and you’ll be on track for sweet, delicious ears come late summer.