When to Plant Scallions in San Diego County, CA
What to do in May
May rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in San Diego County, California.
-
Start scallions under lights
Bottom-water once the first true leaves appear — it keeps stems dry and knocks back damping-off.
Looking ahead to June
- First harvests: scallions
Scallions (green onions) are mild-flavored alliums harvested for their slender green tops and white bases. They are quick-growing and perfect for succession planting.
San Diego County, California is in USDA Zone 10b. The average last spring frost is April 16 and the first fall frost is November 1, giving you a growing season of approximately 199 days.
At an elevation of 2,613 feet, San Diego County receives approximately 18.2 inches of rainfall annually with predominantly loam soil. Summer highs average 92°F, providing good warmth for Scallions during the growing season. With low rainfall, drip irrigation is essential for growing Scallions successfully. Mulch heavily to conserve soil moisture.
San Diego County Soil Profile
Soil Type
Loam
Soil pH
5.7-7.5
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 San Diego County
How your county's soil matches Scallions's growing requirements.
Soil pH
Your soil pH (5.7–7.5) overlaps with Scallions's range (6.0–7.0), though not a perfect match.
Soil Texture
The loam soil in San Diego County is excellent for Scallions — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (2.4%). Annual compost additions will help Scallions.
How to Plant Scallions
Fall planting: Sow 8 weeks before your first frost date for a fall harvest.
Succession Planting Scallions
Sow every 5.7 weeks. Last sowing by Aug 23 to harvest before frost.
For a dedicated fall crop, sow by Sep 06.
Plant Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Scallions
Scallions needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Scallions Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 3" | 0" | ❄️ Dormant |
| Feb | — | 3.9" | 0" | ❄️ Dormant |
| Mar | — | 3.1" | 0" | ❄️ Dormant |
| Apr | 4.3" | 1.4" | 2.9" | 🚿 Regular watering |
| May | 4.3" | 0.5" | 3.8" | 🚿 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" | 0.2" | 4.1" | 🚿 Regular watering |
| Oct | 4.3" | 0.8" | 3.5" | 🚿 Regular watering |
| Nov | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Dec | — | 3.3" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Nov in San Diego County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Scallions 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.
Scallions Planting Timeline — San Diego County, CA
Scallions Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 19 | Mar 19 – Apr 2 |
| Transplant Outdoors | April 16 | Apr 16 – Apr 30 |
| Direct Sow | March 26 | Mar 26 – Apr 16 |
| Harvest | June 11 | Jun 11 – Jul 9 |
| Fall Sowing | September 6 | Sep 6 – Sep 20 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors Direct Sow |
| April | Start Indoors Transplant Outdoors Direct Sow |
| May | — |
| June | Harvest |
| July | Harvest |
| August | — |
| September | Fall Sowing |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 2-3 times/week
📅 Days to Maturity
50–70 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 10b
📆 Growing Season
199 days in San Diego County
Growing Tips for Scallions in San Diego County
Direct sow Scallions outdoors after April 16 in San Diego County when soil has warmed and frost danger has passed.
Common pests for Scallions in this region include onion maggots and thrips. Use row covers early in the season and inspect plants weekly.
San Diego County receives only 18" of rain annually. Scallions needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Direct sow every 3 weeks for continuous harvest. Thin to 1 inch apart or grow in clusters. Harvest when pencil-thick by pulling or cutting at soil level.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Scallions in Other Locations
Frequently Asked Questions
When should I plant Scallions in San Diego County, CA?
San Diego County is in Zone 10b with an average last frost of April 16. Plan your Scallions planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Diego County, CA?
San Diego County, California is in USDA Hardiness Zone 10b. The average last spring frost is April 16 and first fall frost is November 1.
Your San Diego County Garden Planner — Free
A 24-page printable planner built for San Diego 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.