When to Plant Rosemary in Sonoma County, CA
May to-do list for Sonoma County, California
Your Sonoma County, California garden is entering a new phase. Here's what's on the schedule for May and why each task matters now.
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Collect rosemary at their peak
The more you pick, the more the plant produces. Letting fruit overripen tells the plant it's time to stop.
Get ahead of June
- First harvests: rosemary
Rosemary is an aromatic evergreen shrub with needle-like leaves and a piney, citrus flavor. It is a Mediterranean herb that thrives in warm, dry conditions.
Sonoma 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 91 feet, Sonoma County receives approximately 31.1 inches of rainfall annually with predominantly sandy loam soil. Summer highs average 90°F, providing good warmth for Rosemary during the growing season. Sandy soil warms quickly in spring — great for early planting — but Rosemary will need more frequent watering and organic matter to retain nutrients.
Sonoma County Soil Profile
Soil Type
Sandy Loam
Soil pH
5.9-7
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 Sonoma County
How your county's soil matches Rosemary's growing requirements.
Soil pH
Your soil pH (5.9–7.0) overlaps with Rosemary's range (6.0–7.5), though not a perfect match.
Soil Texture
Sandy soil in Sonoma County warms quickly in spring but drains fast. Rosemary will need more frequent watering and regular compost additions to retain nutrients.
Drainage
Drainage is adequate for Rosemary.
Organic Matter
Organic matter is moderate (2.5%). Annual compost additions will help Rosemary.
How to Plant Rosemary
Succession Planting Rosemary
Sow every 9.1 weeks. Last sowing by May 30 to harvest before frost.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Rosemary
Rosemary needs approximately 0.3 inches of water per week (1.3" per month). Here's how your county's rainfall compares month by month.
| Month | Rosemary Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 6.2" | 0" | ❄️ Dormant |
| Feb | 1.3" | 6.8" | 0" | ✅ Rainfall sufficient |
| Mar | 1.3" | 5.2" | 0" | ✅ Rainfall sufficient |
| Apr | 1.3" | 2.3" | 0" | ✅ Rainfall sufficient |
| May | 1.3" | 0.8" | 0.5" | 💧 Light watering |
| Jun | 1.3" | 0.1" | 1.2" | 🚿 Regular watering |
| Jul | 1.3" | 0" | 1.3" | 🚿 Regular watering |
| Aug | 1.3" | 0" | 1.3" | 🚿 Regular watering |
| Sep | 1.3" | 0.4" | 0.9" | 🚿 Regular watering |
| Oct | 1.3" | 1.3" | 0" | ✅ Rainfall sufficient |
| Nov | 1.3" | 2.7" | 0" | ✅ Rainfall sufficient |
| Dec | — | 5.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Feb–Nov in Sonoma County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Rosemary 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.
Rosemary Planting Timeline — Sonoma County, CA
Rosemary Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Transplant Outdoors | March 5 | Mar 5 – Mar 19 |
| Harvest | May 28 | May 28 – Oct 15 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Transplant Outdoors |
| April | — |
| May | Harvest |
| June | Harvest |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.3"/week · Natural rainfall sufficient
📅 Days to Maturity
80–180 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 9b
📆 Growing Season
273 days in Sonoma County
Growing Tips for Rosemary in Sonoma County
Direct sow Rosemary outdoors after February 26 in Sonoma County when soil has warmed and frost danger has passed.
Sandy soil in Sonoma County dries quickly — mulch Rosemary with 2-3 inches of straw and water deeply 2-3 times per week rather than lightly every day.
General growing tips
Grow in well-drained soil and avoid overwatering. In cold climates, grow in containers and bring indoors for winter. Propagate from stem cuttings for faster results than seed.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Rosemary in Other Locations
Frequently Asked Questions
When should I plant Rosemary in Sonoma County, CA?
Sonoma County is in Zone 9b with an average last frost of February 26. Plan your Rosemary planting based on this frost date — see the calendar above for exact timing.
What planting zone is Sonoma County, CA?
Sonoma County, California is in USDA Hardiness Zone 9b. The average last spring frost is February 26 and first fall frost is November 26.
Your Sonoma County Garden Planner — Free
A 24-page printable planner built for Sonoma 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.