When to Plant Onion in Florence County, WI
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.
Florence County, Wisconsin is in USDA Zone 4a. The average last spring frost is May 26 and the first fall frost is September 21, giving you a growing season of approximately 118 days.
At an elevation of 1,147 feet, Florence County receives approximately 34.5 inches of rainfall annually with predominantly silt loam soil. Summer highs average 82°F, so choose short-season varieties of Onion to ensure they mature before fall.
Florence County Soil Profile
Soil Type
Silt Loam
Soil pH
5.8-6.8
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 Florence County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (5.8–6.8) overlaps with Onion's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Florence County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (4.4%) — Onion will thrive.
How to Plant Onion
Fall planting: Sow 12 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 | — | 1.2" | 0" | ❄️ Dormant |
| Feb | — | 1.4" | 0" | ❄️ Dormant |
| Mar | — | 2.6" | 0" | ❄️ Dormant |
| Apr | — | 3.4" | 0" | ❄️ Dormant |
| May | 4.3" | 4.4" | 0" | ✅ Rainfall sufficient |
| Jun | 4.3" | 4.4" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 3.2" | 1.1" | 💧 Light watering |
| Aug | 4.3" | 4" | 0.3" | 💧 Light watering |
| Sep | 4.3" | 2.9" | 1.4" | 💧 Light watering |
| Oct | — | 2.7" | 0" | ❄️ Dormant |
| Nov | — | 2.4" | 0" | ❄️ Dormant |
| Dec | — | 1.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Florence 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 — Florence County, WI
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | April 14 | Apr 14 – Apr 28 |
| Transplant Outdoors | May 26 | May 26 – Jun 9 |
| Direct Sow | May 19 | May 19 – Jun 9 |
| Harvest | August 25 | Aug 25 – Oct 13 |
| Fall Sowing | June 29 | Jun 29 – Jul 13 |
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 | Transplant Outdoors Direct Sow Fall Sowing |
| July | Fall Sowing |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · Natural rainfall sufficient
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 4a
📆 Growing Season
118 days in Florence County
Growing Tips for Onion in Florence County
Direct sow Onion outdoors after May 26 in Florence County when soil has warmed and frost danger has passed.
Your 118.0-day growing season in Florence County is tight for Onion (90.0-120.0 days to maturity). Start indoors and choose early-maturing varieties.
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
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Onion in Other Locations
Frequently Asked Questions
When should I plant Onion in Florence County, WI?
Florence County is in Zone 4a with an average last frost of May 26. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Florence County, WI?
Florence County, Wisconsin is in USDA Hardiness Zone 4a. The average last spring frost is May 26 and first fall frost is September 21.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Florence County gardeners in Zone 4a organize planting dates, track what's growing, and never miss a planting window.
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