When to Plant Brussels Sprouts in Marin County, CA
Your May gardening checklist
Welcome to May in Zone 9b. These are the moves that will have the biggest impact on your growing season.
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Harvest brussels sprouts as they ripen
This is the payoff month. Bring a basket, bring a friend, and get into the beds.
June prep starts now
- First harvests: brussels sprouts
Brussels sprouts are a cold-hardy brassica that produces miniature cabbage-like heads along a tall stalk. Flavor improves after a light frost.
Marin County, California is in USDA Zone 9b. The average last spring frost is February 26 and the first fall frost is November 26, giving you a growing season of approximately 273 days.
At an elevation of 302 feet, Marin County receives approximately 36 inches of rainfall annually with predominantly sandy loam soil. Summer highs average 81°F, so choose short-season varieties of Brussels Sprouts to ensure they mature before fall. Sandy soil warms quickly in spring — great for early planting — but Brussels Sprouts will need more frequent watering and organic matter to retain nutrients.
Marin County Soil Profile
Soil Type
Sandy Loam
Soil pH
6-6.9
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 Marin County
How your county's soil matches Brussels Sprouts's growing requirements.
Soil pH
Your soil pH (6.0–6.9) is within Brussels Sprouts's preferred range (6.0–7.5).
Soil Texture
Sandy soil in Marin County warms quickly in spring but drains fast. Brussels Sprouts will need more frequent watering and regular compost additions to retain nutrients.
Organic Matter
Organic matter is moderate (2.3%). Annual compost additions will help Brussels Sprouts.
How to Plant Brussels Sprouts
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 Brussels Sprouts
Brussels Sprouts needs approximately 0.9 inches of water per week (3.9" per month). Here's how your county's rainfall compares month by month.
| Month | Brussels Sprouts Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 7.2" | 0" | ❄️ Dormant |
| Feb | 3.9" | 6.5" | 0" | ✅ Rainfall sufficient |
| Mar | 3.9" | 6.2" | 0" | ✅ Rainfall sufficient |
| Apr | 3.9" | 2.7" | 1.2" | 💧 Light watering |
| May | 3.9" | 1" | 2.9" | 🚿 Regular watering |
| Jun | 3.9" | 0.2" | 3.7" | 🚿 Regular watering |
| Jul | 3.9" | 0" | 3.9" | 🚿 Regular watering |
| Aug | 3.9" | 0" | 3.9" | 🚿 Regular watering |
| Sep | 3.9" | 0.4" | 3.5" | 🚿 Regular watering |
| Oct | 3.9" | 1.4" | 2.5" | 🚿 Regular watering |
| Nov | 3.9" | 3.5" | 0.4" | 💧 Light watering |
| Dec | — | 6.9" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Feb–Nov in Marin County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Brussels Sprouts 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.
Brussels Sprouts Planting Timeline — Marin County, CA
Brussels Sprouts Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | January 29 | Jan 29 – Feb 12 |
| Transplant Outdoors | February 26 | Feb 26 – Mar 12 |
| Direct Sow | February 5 | Feb 5 – Feb 26 |
| Harvest | May 28 | May 28 – Jul 23 |
| Fall Sowing | October 1 | Oct 1 – Oct 15 |
Plant 1" deep · 15" apart · Rows 24" 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
0.9"/week · 1-2 times/week
📅 Days to Maturity
90–130 days
🧪 Soil pH
Needs 6–7.5 · Your soil: ideal
🗺️ USDA Zone
Zone 9b
📆 Growing Season
273 days in Marin County
Growing Tips for Brussels Sprouts in Marin County
Direct sow Brussels Sprouts outdoors after February 26 in Marin County when soil has warmed and frost danger has passed.
Sandy soil in Marin County dries quickly — mulch Brussels Sprouts with 2-3 inches of straw and water deeply 2-3 times per week rather than lightly every day.
Common pests for Brussels Sprouts in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
General growing tips
Start seeds indoors 12-14 weeks before first fall frost. Stake tall plants to prevent toppling. Remove lower leaves as sprouts develop to improve air circulation.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Brussels Sprouts in Other Locations
Frequently Asked Questions
When should I plant Brussels Sprouts in Marin County, CA?
Marin County is in Zone 9b with an average last frost of February 26. Plan your Brussels Sprouts planting based on this frost date — see the calendar above for exact timing.
What planting zone is Marin County, CA?
Marin County, California is in USDA Hardiness Zone 9b. The average last spring frost is February 26 and first fall frost is November 26.
Your Marin County Garden Planner — Free
A 24-page printable planner built for Marin 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.