When to Plant Onion in Mason County, MI
Your May gardening checklist
Welcome to May in Zone 6a. These are the moves that will have the biggest impact on your growing season.
-
Time to transplant onion
Your last frost (May 15) has passed. These warm-season crops can handle outdoor soil now.
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Scatter onion into prepared beds
These tolerate cool soil, so you're not gambling by sowing now.
Get ahead of June
- Starting indoors: onion
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, Michigan is in USDA Zone 6a. The average last spring frost is May 15 and the first fall frost is October 7, giving you a growing season of approximately 145 days.
At an elevation of 1,318 feet, Mason County receives approximately 34.4 inches of rainfall annually with predominantly silt loam soil. Summer highs average 85°F, providing good warmth for Onion during the growing season.
Mason County Soil Profile
Soil Type
Silt Loam
Soil pH
6-7.3
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.
Soil Compatibility in Mason County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.0–7.3) overlaps with Onion's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Mason County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (4.5%) — Onion will thrive.
How to Plant Onion
Fall planting: Sow 10 weeks before your first frost date for a fall harvest.
Plant Water Budget
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 | — | 1.3" | 0" | ❄️ Dormant |
| Feb | — | 1.7" | 0" | ❄️ Dormant |
| Mar | — | 2.5" | 0" | ❄️ Dormant |
| Apr | — | 3.1" | 0" | ❄️ Dormant |
| May | 4.3" | 3.3" | 1" | 💧 Light watering |
| Jun | 4.3" | 4.5" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 4.1" | 0.2" | 💧 Light watering |
| Aug | 4.3" | 3.9" | 0.4" | 💧 Light watering |
| Sep | 4.3" | 3.3" | 1" | 💧 Light watering |
| Oct | 4.3" | 2.9" | 1.4" | 💧 Light watering |
| Nov | — | 2.1" | 0" | ❄️ Dormant |
| Dec | — | 1.7" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Oct in Mason County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Onion Heat Requirements (GDD)
What are Growing Degree Days (GDD)?
Growing Degree Days measure the total warmth your plants receive during the growing season. Think of it as a "heat bank" — every day above 50°F deposits warmth that helps your plants grow.
Each plant needs a certain amount of accumulated heat to mature. If your county provides more GDD than the plant needs, it's a great fit. If it's close, you may want to choose faster-maturing varieties or start seeds indoors to get a head start.
Onion Planting Timeline — Mason County, MI
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 10 | Apr 10 – Apr 24 |
| Transplant Outdoors | May 15 | May 15 – May 29 |
| Direct Sow | May 1 | May 1 – May 22 |
| Harvest | August 14 | Aug 14 – Oct 2 |
| Fall Sowing | July 29 | Jul 29 – Aug 12 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | Start Indoors |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | Fall Sowing |
| August | Fall Sowing Harvest |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · Only during dry spells
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 6a
📆 Growing Season
145 days in Mason County
Growing Tips for Onion in Mason County
Direct sow Onion outdoors after May 15 in Mason County when soil has warmed and frost danger has passed.
Common pests for Onion in this region include onion maggots and thrips. Use row covers early in the season and inspect plants weekly.
General growing tips
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 Mason County, MI?
Mason County is in Zone 6a with an average last frost of May 15. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Mason County, MI?
Mason County, Michigan is in USDA Hardiness Zone 6a. The average last spring frost is May 15 and first fall frost is October 7.
Your Mason County Garden Planner — Free
A 24-page printable planner built for Mason 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.