When to Plant Onion in San Francisco County, CA
May to-do list for San Francisco County, California
A quick May briefing for San Francisco County, California gardeners — what's urgent, what's next, and what can wait.
-
Pick onion
Check every 1–2 days. Many of these get tough or go to seed if you wait too long.
Coming up in June — start thinking about
- 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.
San Francisco County, California is in USDA Zone 10b. The average last spring frost is February 23 and the first fall frost is November 27, giving you a growing season of approximately 277 days.
At an elevation of 412 feet, San Francisco County receives approximately 13.5 inches of rainfall annually with predominantly loam soil. Summer highs average 86°F, providing good warmth for Onion during the growing season. With low rainfall, drip irrigation is essential for growing Onion successfully. Mulch heavily to conserve soil moisture.
San Francisco County Soil Profile
Soil Type
Loam
Soil pH
6.2-7.2
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 San Francisco County
How your county's soil matches Onion's growing requirements.
Soil pH
Your soil pH (6.2–7.2) overlaps with Onion's range (6.0–7.0), though not a perfect match.
Soil Texture
The loam soil in San Francisco County is excellent for Onion — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.0%). 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 8/10 — 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 | — | 2.3" | 0" | ❄️ Dormant |
| Feb | 4.3" | 3.1" | 1.2" | 💧 Light watering |
| Mar | 4.3" | 2.2" | 2.1" | 💧 Light watering |
| Apr | 4.3" | 1.2" | 3.1" | 🚿 Regular watering |
| May | 4.3" | 0.3" | 4" | 🚿 Regular watering |
| Jun | 4.3" | 0.1" | 4.2" | 🚿 Regular watering |
| Jul | 4.3" | 0" | 4.3" | 🚿 Regular watering |
| Aug | 4.3" | 0" | 4.3" | 🚿 Regular watering |
| Sep | 4.3" | 0.1" | 4.2" | 🚿 Regular watering |
| Oct | 4.3" | 0.6" | 3.7" | 🚿 Regular watering |
| Nov | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| Dec | — | 2.1" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Feb–Nov in San Francisco 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 — San Francisco County, CA
Onion Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | January 26 | Jan 26 – Feb 9 |
| Transplant Outdoors | February 23 | Feb 23 – Mar 9 |
| Direct Sow | February 2 | Feb 2 – Feb 23 |
| Harvest | May 25 | May 25 – Jul 13 |
| Fall Sowing | October 2 | Oct 2 – Oct 16 |
Plant 1" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Start Indoors |
| February | Start Indoors Transplant Outdoors Direct Sow |
| March | Transplant Outdoors |
| April | — |
| May | Harvest |
| June | Harvest |
| July | Harvest |
| August | — |
| September | — |
| October | Fall Sowing |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 2-3 times/week
📅 Days to Maturity
90–120 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 10b
📆 Growing Season
277 days in San Francisco County
Growing Tips for Onion in San Francisco County
Direct sow Onion outdoors after February 23 in San Francisco 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.
San Francisco County receives only 14" of rain annually. Onion needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
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 San Francisco County, CA?
San Francisco County is in Zone 10b with an average last frost of February 23. Plan your Onion planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Francisco County, CA?
San Francisco County, California is in USDA Hardiness Zone 10b. The average last spring frost is February 23 and first fall frost is November 27.
Your San Francisco County Garden Planner — Free
A 24-page printable planner built for San Francisco County (Zone 10b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.