When to Plant Potatoes in Mercer County, IL
Potatoes are a versatile staple crop that produces tubers underground. They come in hundreds of varieties with varying colors, textures, and maturity dates.
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 Potatoes 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
Potatoes Planting Timeline — Mercer County, IL
Potatoes Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 20 | Feb 20 – Mar 6 |
| Transplant Outdoors | May 1 | May 1 – May 15 |
| Direct Sow | April 24 | Apr 24 – May 15 |
| Harvest | July 10 | Jul 10 – Sep 18 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors |
| April | Direct Sow |
| May | Transplant Outdoors 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
70–120 days
Soil pH
5 – 6.5
USDA Zone
Zone 5a
Growing Season
181 days
Growing Tips for Mercer County
Plant seed potatoes (not grocery store potatoes) 4 inches deep in spring. Hill soil around stems as plants grow to prevent greening. Stop watering when plants die back.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Potatoes in Other Locations
Frequently Asked Questions
When should I plant Potatoes in Mercer County, IL?
Mercer County is in Zone 5a with an average last frost of April 17. Plan your Potatoes 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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