When to Plant Soybeans in Mercer County, IL
Soybeans (edamame) are a high-protein legume that fixes nitrogen in the soil. Fresh green soybeans harvested at the edamame stage are a nutritious snack.
Mercer County, Illinois is in USDA Zone 5a. The average last spring frost is April 17 and the first fall frost is October 15, giving you a growing season of approximately 181 days.
At an elevation of 777 feet, Mercer County receives approximately 37.2 inches of rainfall annually with predominantly silt loam soil. Summer highs average 83°F, so choose short-season varieties of Soybeans to ensure they mature before fall.
Mercer County Soil Profile
Soil Type
Silt Loam
Soil pH
6.3-6.7
Drainage
Well Drained
Plant Planting Risk Windows
Percentages indicate frost risk at transplant. The 70% safe window means there is a 30% chance of frost after transplant — suitable for cold-hardy crops or gardeners with frost protection. The 90% safe window is best for tender plants.
Plant Water Budget
Soybeans Planting Timeline — Mercer County, IL
Soybeans Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Direct Sow | April 24 | Apr 24 – May 15 |
| Harvest | July 17 | Jul 17 – Sep 11 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Direct Sow |
| May | Direct Sow |
| June | — |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
80–120 days
Soil pH
6 – 7
USDA Zone
Zone 5a
Growing Season
181 days
Growing Tips for Mercer County
Direct sow after soil warms to 60F. Plant in blocks rather than rows for better pollination. Harvest for edamame when pods are plump and bright green.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Soybeans in Other Locations
Frequently Asked Questions
When should I plant Soybeans in Mercer County, IL?
Mercer County is in Zone 5a with an average last frost of April 17. Plan your Soybeans planting based on this frost date — see the calendar above for exact timing.
What planting zone is Mercer County, IL?
Mercer County, Illinois is in USDA Hardiness Zone 5a. The average last spring frost is April 17 and first fall frost is October 15.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Mercer County gardeners in Zone 5a organize planting dates, track what's growing, and never miss a planting window.
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