When to Plant Onion in Henderson County, NC
Your May planting checklist for Henderson County, North Carolina
Each item below is timed to Henderson County, North Carolina's frost dates and soil temperatures. Skip nothing, stress about nothing.
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Time to start onion inside
A seed-starting mix and a sunny window (or a grow light) are all you need. Keep soil warm — around 70°F — for fast germination.
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.
Henderson County, North Carolina is in USDA Zone 7b. The average last spring frost is April 10 and the first fall frost is October 26, giving you a growing season of approximately 199 days.
At an elevation of 1,829 feet, Henderson County receives approximately 52.9 inches of rainfall annually with predominantly clay loam soil. Summer highs average 92°F, providing good warmth for Onion during the growing season. Clay soil retains moisture well for Onion, but amend with compost to improve drainage and prevent root rot. Ample rainfall means less supplemental watering, but ensure good drainage to prevent Onion root diseases.
Henderson County Soil Profile
Soil Type
Clay Loam
Soil pH
5.2-6.5
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 Henderson County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (5.2–6.5) is more acidic than Onion prefers (6.0–7.0). Add garden lime to raise pH.
Soil Texture
The clay loam soil in Henderson County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Onion.
Organic Matter
Organic matter is moderate (2.6%). Annual compost additions will help Onion.
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 | — | 3.7" | 0" | ❄️ Dormant |
| Feb | — | 4.2" | 0" | ❄️ Dormant |
| Mar | — | 4.9" | 0" | ❄️ Dormant |
| Apr | 4.3" | 4.4" | 0" | ✅ Rainfall sufficient |
| May | 4.3" | 3.7" | 0.6" | 💧 Light watering |
| Jun | 4.3" | 5.2" | 0" | ✅ Rainfall sufficient |
| Jul | 4.3" | 6.2" | 0" | ✅ Rainfall sufficient |
| Aug | 4.3" | 4.4" | 0" | ✅ Rainfall sufficient |
| Sep | 4.3" | 4.5" | 0" | ✅ Rainfall sufficient |
| Oct | 4.3" | 3" | 1.3" | 💧 Light watering |
| Nov | — | 4.1" | 0" | ❄️ Dormant |
| Dec | — | 4.5" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Henderson 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 — Henderson County, NC
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 6 | Mar 6 – Mar 20 |
| Transplant Outdoors | April 10 | Apr 10 – Apr 24 |
| Direct Sow | March 27 | Mar 27 – Apr 17 |
| Harvest | July 10 | Jul 10 – Aug 28 |
| Fall Sowing | August 17 | Aug 17 – Aug 31 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors Direct Sow |
| April | Transplant Outdoors Direct Sow |
| May | — |
| June | — |
| July | Harvest |
| August | Fall Sowing Harvest |
| September | — |
| October | — |
| 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: too_acidic
🗺️ USDA Zone
Zone 7b
📆 Growing Season
199 days in Henderson County
Growing Tips for Onion in Henderson County
Direct sow Onion outdoors after April 10 in Henderson County when soil has warmed and frost danger has passed.
With Henderson County's clay soil (31% clay), work in 3-4 inches of compost before planting Onion. Avoid tilling when soil is wet to prevent compaction.
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 Henderson County, NC?
Henderson County is in Zone 7b with an average last frost of April 10. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is Henderson County, NC?
Henderson County, North Carolina is in USDA Hardiness Zone 7b. The average last spring frost is April 10 and first fall frost is October 26.
Your Henderson County Garden Planner — Free
A 24-page printable planner built for Henderson County (Zone 7b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.