When to Plant Onion in Mason County, IL
Onions are a fundamental kitchen staple available in yellow, white, and red varieties. Choose long-day, short-day, or intermediate types based on your latitude.
Mason County, Illinois is in USDA Zone 5b. The average last spring frost is April 15 and the first fall frost is October 14, giving you a growing season of approximately 182 days.
At an elevation of 768 feet, Mason County receives approximately 30.4 inches of rainfall annually with predominantly silt loam soil. Summer highs average 86°F, providing good warmth for Onion during the growing season.
Mason County Soil Profile
Soil Type
Silt Loam
Soil pH
6.1-6.9
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
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Onion Planting Timeline — Mason County, IL
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 11 | Mar 11 – Mar 25 |
| Transplant Outdoors | April 15 | Apr 15 – Apr 29 |
| Direct Sow | April 1 | Apr 1 – Apr 22 |
| Fall Sowing | August 5 | Aug 5 – Aug 19 |
| Harvest | July 15 | Jul 15 – Sep 2 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Transplant Outdoors Direct Sow |
| May | — |
| June | — |
| July | Harvest |
| August | Fall Sowing Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
6 – 7
USDA Zone
Zone 5b
Growing Season
182 days
Growing Tips for Mason County
Start seeds indoors 8-10 weeks before transplanting. Match day-length type to your latitude. Stop watering when tops begin to fall over and cure bulbs for 2-3 weeks before storage.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in Mason County, IL?
Mason County is in Zone 5b with an average last frost of April 15. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Mason County, IL?
Mason County, Illinois is in USDA Hardiness Zone 5b. The average last spring frost is April 15 and first fall frost is October 14.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Mason County gardeners in Zone 5b organize planting dates, track what's growing, and never miss a planting window.
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