When to plant Leeks in Millbrae, CA
For Millbrae, gardeners: plant Leeks December 28 through January 18 once soil reads 50°F. A second sowing from October 17 to October 31 extends the harvest into fall.
When to Plant Leeks in Millbrae, CA
July in San Mateo County, California — your action list
July is a pivotal month for San Mateo County, California gardens. Focus on these tasks first and you'll set up the rest of the season for success.
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Bring in the leeks
This is the payoff month. Bring a basket, bring a friend, and get into the beds.
Leeks are a mild, sweet allium that produces long white shanks. They are more refined than onions and are a key ingredient in soups, stews, and gratins.
Millbrae, California is in USDA Zone 10a. The average last spring frost is January 18 and the first fall frost is December 12, giving you a growing season of approximately 328 days.
At an elevation of 277 feet, San Mateo County receives approximately 16.9 inches of rainfall annually with predominantly loam soil. Summer highs average 81°F, so choose short-season varieties of Leeks to ensure they mature before fall. With low rainfall, drip irrigation is essential for growing Leeks successfully. Mulch heavily to conserve soil moisture.
Millbrae Soil Profile
Soil Type
Loam
Soil pH
6.8-7.2
Drainage
Well Drained
Leeks 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 Millbrae
How your county's soil matches Leeks's growing requirements.
Soil pH
Your soil pH (6.8–7.2) overlaps with Leeks's range (6.0–7.0), though not a perfect match.
Soil Texture
The loam soil in San Mateo County is excellent for Leeks — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Leeks.
Organic Matter
Organic matter is moderate (2.6%). Annual compost additions will help Leeks.
How to Plant Leeks
Fall planting: Sow 8 weeks before your first frost date for a fall harvest.
Leeks Water Budget
Water stress score is 8/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Leeks
Leeks needs approximately 0.8 inches of water per week (3.5" per month). Here's how your county's rainfall compares month by month.
| Month | Leeks Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | 3.5" | 3.9" | 0" | ✅ Rainfall sufficient |
| Feb | 3.5" | 3.4" | 0.1" | 💧 Light watering |
| Mar | 3.5" | 2.7" | 0.8" | 💧 Light watering |
| Apr | 3.5" | 1.2" | 2.3" | 🚿 Regular watering |
| May | 3.5" | 0.4" | 3.1" | 🚿 Regular watering |
| Jun | 3.5" | 0.1" | 3.4" | 🚿 Regular watering |
| Jul | 3.5" | 0" | 3.5" | 🚿 Regular watering |
| Aug | 3.5" | 0" | 3.5" | 🚿 Regular watering |
| Sep | 3.5" | 0.2" | 3.3" | 🚿 Regular watering |
| Oct | 3.5" | 0.7" | 2.8" | 🚿 Regular watering |
| Nov | 3.5" | 1.4" | 2.1" | 🚿 Regular watering |
| Dec | 3.5" | 2.9" | 0.6" | 💧 Light watering |
Water needs are for active growing months only (Jan–Dec in San Mateo County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Leeks 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.
Leeks Planting Timeline — Millbrae, CA
Leeks Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | December 21 | Dec 21 – Jan 4 |
| Transplant Outdoors | January 18 | Jan 18 – Feb 1 |
| Direct Sow | December 28 | Dec 28 – Jan 18 |
| Harvest | April 19 | Apr 19 – Jul 5 |
| Fall Sowing | October 17 | Oct 17 – Oct 31 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Start Indoors Transplant Outdoors Direct Sow |
| February | Transplant Outdoors |
| March | — |
| April | Harvest |
| May | Harvest |
| June | Harvest |
| July | Harvest |
| August | — |
| September | — |
| October | Fall Sowing |
| November | — |
| December | Start Indoors Direct Sow |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.8"/week · 2-3 times/week
📅 Days to Maturity
90–150 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 10a
📆 Growing Season
328 days in San Mateo County
Growing Tips for Leeks in Millbrae
Direct sow Leeks outdoors after January 18 in San Mateo County when soil has warmed and frost danger has passed.
Common pests for Leeks 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 10-12 weeks before last frost. Transplant into trenches and hill soil around stems as they grow to increase the white portion. Harvest as needed.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Leeks in Other Locations
When should I plant Leeks in Millbrae, CA?
In Millbrae, CA, plant Leeks after the last frost (around January 18) and before the first frost (around December 12). Best results when soil holds above 50°F.
What growing zone is Millbrae, CA for Leeks?
Millbrae sits in USDA Zone 10a. Leeks grows reliably in zones 3a through 10b, so it's a good fit here.
Can Leeks grow in Millbrae's climate?
Yes — Leeks grows well in Millbrae's temperate climate. Millbrae averages a 329-day frost-free season, with last frost around January 18 and first frost around December 12.
Your San Mateo County Garden Planner — Free
A 22-page printable planner built for San Mateo County (Zone 10a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.