When to Plant Onion in El Dorado County, CA
Your May gardening checklist
Your El Dorado County, California garden is entering a new phase. Here's what's on the schedule for May and why each task matters now.
-
Time to start onion inside
Your window is short. These crops want several weeks of indoor growth before they go outside.
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.
El Dorado County, California is in USDA Zone 9b. The average last spring frost is April 11 and the first fall frost is November 22, giving you a growing season of approximately 225 days.
At an elevation of 2,714 feet, El Dorado County receives approximately 41 inches of rainfall annually with predominantly loam soil. Summer highs average 83°F, so choose short-season varieties of Onion to ensure they mature before fall.
El Dorado County Soil Profile
Soil Type
Loam
Soil pH
6.3-7.2
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 El Dorado County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.3–7.2) overlaps with Onion's range (6.0–7.0), though not a perfect match.
Soil Texture
The loam soil in El Dorado County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.9%). Annual compost additions will help Onion.
How to Plant Onion
Fall planting: Sow 8 weeks before your first frost date for a fall harvest.
Plant 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 | — | 7.5" | 0" | ❄️ Dormant |
| Feb | — | 9.2" | 0" | ❄️ Dormant |
| Mar | — | 7" | 0" | ❄️ Dormant |
| Apr | 4.3" | 3.4" | 0.9" | 💧 Light watering |
| May | 4.3" | 1.1" | 3.2" | 🚿 Regular watering |
| Jun | 4.3" | 0.2" | 4.1" | 🚿 Regular watering |
| Jul | 4.3" | 0" | 4.3" | 🚿 Regular watering |
| Aug | 4.3" | 0" | 4.3" | 🚿 Regular watering |
| Sep | 4.3" | 0.5" | 3.8" | 🚿 Regular watering |
| Oct | 4.3" | 1.6" | 2.7" | 🚿 Regular watering |
| Nov | 4.3" | 3.8" | 0.5" | 💧 Light watering |
| Dec | — | 6.8" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Nov in El Dorado 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 — El Dorado County, CA
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 14 | Mar 14 – Mar 28 |
| Transplant Outdoors | April 11 | Apr 11 – Apr 25 |
| Direct Sow | March 21 | Mar 21 – Apr 11 |
| Harvest | July 11 | Jul 11 – Aug 29 |
| Fall Sowing | September 27 | Sep 27 – Oct 11 |
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 | Harvest |
| September | Fall Sowing |
| October | Fall Sowing |
| 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 9b
📆 Growing Season
225 days in El Dorado County
Growing Tips for Onion in El Dorado County
Direct sow Onion outdoors after April 11 in El Dorado 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 El Dorado County, CA?
El Dorado County is in Zone 9b with an average last frost of April 11. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is El Dorado County, CA?
El Dorado County, California is in USDA Hardiness Zone 9b. The average last spring frost is April 11 and first fall frost is November 22.
Your El Dorado County Garden Planner — Free
A 24-page printable planner built for El Dorado County (Zone 9b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.