When to plant Onion in Stephenson County County,
Plant Onion in Stephenson County County from April 9 to April 30 in spring. Stephenson County County sits in USDA Zone 5a, with last frost around April 23 and first frost on October 13. A second sowing from August 4 to August 18 extends the harvest into fall.
When to Plant Onion in Stephenson County, IL
Stephenson County, Illinois gardeners: here's your June plan
Your Stephenson County, Illinois garden is entering a new phase. Here's what's on the schedule for June and why each task matters now.
To set up a strong July, finish these tasks
- First harvests: 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.
Stephenson County, Illinois is in USDA Zone 5a. The average last spring frost is April 23 and the first fall frost is October 13, giving you a growing season of approximately 173 days.
At an elevation of 1,345 feet, Stephenson County receives approximately 36.2 inches of rainfall annually with predominantly silt loam soil. Summer highs average 85°F, providing good warmth for Onion during the growing season.
Stephenson County Soil Profile
Soil Type
Silt Loam
Soil pH
6.2-7.1
Drainage
Well Drained
Onion 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 Stephenson County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.2–7.1) overlaps with Onion's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Stephenson 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.
Onion Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
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 | — | 1.7" | 0" | ❄️ Dormant |
| Feb | — | 1.5" | 0" | ❄️ Dormant |
| Mar | — | 2.5" | 0" | ❄️ Dormant |
| Apr | 4.3" | 3.3" | 1" | 💧 Light watering |
| May | 4.3" | 4.7" | 0" | ✅ Rainfall sufficient |
| Jun | 4.3" | 4" | 0.3" | 💧 Light watering |
| Jul | 4.3" | 4.1" | 0.2" | 💧 Light watering |
| Aug | 4.3" | 3.9" | 0.4" | 💧 Light watering |
| Sep | 4.3" | 3.5" | 0.8" | 💧 Light watering |
| Oct | 4.3" | 2.4" | 1.9" | 💧 Light watering |
| Nov | — | 2.3" | 0" | ❄️ Dormant |
| Dec | — | 2.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Stephenson 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 — Stephenson County, IL
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 19 | Mar 19 – Apr 2 |
| Transplant Outdoors | April 23 | Apr 23 – May 7 |
| Direct Sow | April 9 | Apr 9 – Apr 30 |
| Harvest | July 23 | Jul 23 – Sep 10 |
| Fall Sowing | August 4 | Aug 4 – Aug 18 |
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 |
| June | — |
| July | Harvest |
| August | Fall Sowing Harvest |
| September | Harvest |
| October | — |
| 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 5a
📆 Growing Season
173 days in Stephenson County
Growing Tips for Onion in Stephenson County
Direct sow Onion outdoors after April 23 in Stephenson 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 Stephenson County, IL?
Stephenson County is in Zone 5a with an average last frost of April 23. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Stephenson County, IL?
Stephenson County, Illinois is in USDA Hardiness Zone 5a. The average last spring frost is April 23 and first fall frost is October 13.
When should I plant Onion in Stephenson County, ?
In Stephenson County, , plant Onion after the last frost (around April 23) and before the first frost (around October 13). Best results when soil holds above 50°F.
What growing zone is Stephenson County, for Onion?
Stephenson County sits in USDA Zone 5a. Onion grows reliably in zones 3a through 10b, so it's a good fit here.
Can Onion grow in Stephenson County's climate?
Yes — Onion grows well in Stephenson County's temperate climate. Stephenson County averages a 173-day frost-free season, with last frost around April 23 and first frost around October 13.
Your Stephenson County Garden Planner — Free
A 22-page printable planner built for Stephenson County (Zone 5a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.