When to plant Onion in St. Clair County, MI
For Onion in St. Clair County, the safe spring window opens around April 13 and closes around May 4. Last expected frost is April 27, first fall frost October 27, giving a 183-day growing season. A second sowing from August 18 to September 1 extends the harvest into fall.
When to Plant Onion in St. Clair County, MI
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.
St. Clair County, Michigan is in USDA Zone 6a. The average last spring frost is April 27 and the first fall frost is October 27, giving you a growing season of approximately 183 days.
At an elevation of 1,065 feet, St. Clair County receives approximately 38.6 inches of rainfall annually with predominantly silt loam soil. Summer highs average 85°F, providing good warmth for Onion during the growing season.
St. Clair County Soil Profile
Soil Type
Silt Loam
Soil pH
6.1-7.2
Drainage
Well Drained
Monthly Watering Guide for Onion
Onion needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Onion Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 1.6" | 0" | ❄️ Dormant |
| Feb | — | 1.6" | 0" | ❄️ Dormant |
| Mar | — | 3" | 0" | ❄️ Dormant |
| Apr | 4.3" | 3.6" | 0.7" | 💧 Light watering |
| May | 4.3" | 3.9" | 0.4" | 💧 Light watering |
| Jun | 4.3" | 4.5" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 4.4" | 0" | ✅ Rainfall sufficient |
| Aug | 4.3" | 4.6" | 0" | ✅ Rainfall sufficient |
| Sep | 4.3" | 3.4" | 0.9" | 💧 Light watering |
| Oct | 4.3" | 3.3" | 1" | 💧 Light watering |
| Nov | — | 2.7" | 0" | ❄️ Dormant |
| Dec | — | 1.9" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in St. Clair County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Onion Planting Timeline — St. Clair County, MI
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 23 | Mar 23 – Apr 6 |
| Transplant Outdoors | April 27 | Apr 27 – May 11 |
| Direct Sow | April 13 | Apr 13 – May 4 |
| Harvest | July 27 | Jul 27 – Sep 14 |
| Fall Sowing | August 18 | Aug 18 – Sep 1 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Start Indoors Transplant Outdoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Harvest |
| August | Fall Sowing Harvest |
| September | Fall Sowing Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
Moderate — regular watering
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: N/A
🗺️ USDA Zone
Zone 6a
📆 Growing Season
183 days in St. Clair County
Growing Tips for St. Clair 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
Check more plant combinations with our Companion Planting Checker →
Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in St. Clair County, MI?
St. Clair County is in Zone 6a with an average last frost of April 27. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is St. Clair County, MI?
St. Clair County, Michigan is in USDA Hardiness Zone 6a. The average last spring frost is April 27 and first fall frost is October 27.
When should I plant Onion in St. Clair County, MI?
In St. Clair County, MI, plant Onion after the last frost (around April 27) and before the first frost (around October 27). Best results when soil holds above 50°F.
What growing zone is St. Clair County, MI for Onion?
St. Clair County sits in USDA Zone 6a. Onion grows reliably in zones 3a through 10b, so it's a good fit here.
Can Onion grow in St. Clair County's climate?
Yes — Onion grows well in St. Clair County's temperate climate. St. Clair County averages a 183-day frost-free season, with last frost around April 27 and first frost around October 27.
Your St. Clair County Garden Planner — Free
A 22-page printable planner built for St. Clair County (Zone 6a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.