When to Plant Rosemary in Alameda County, CA
Top priorities for Alameda County, California gardeners in May
May rewards gardeners who work with the weather, not against it. Here's how to stay in step this month in Alameda County, California.
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Start harvesting rosemary
Morning harvests are best — cooler temperatures mean crisper produce and longer fridge life.
A few tasks this May that'll pay off in 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.
Alameda County, 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 379 feet, Alameda County receives approximately 16.4 inches of rainfall annually with predominantly loam soil. Summer highs average 97°F, so Rosemary may need afternoon shade and extra watering during peak heat. With low rainfall, drip irrigation is essential for growing Rosemary successfully. Mulch heavily to conserve soil moisture.
Alameda County Soil Profile
Soil Type
Loam
Soil pH
6.3-7.7
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 Alameda County
How your county's soil matches Rosemary's growing requirements.
Soil pH
Your soil pH (6.3–7.7) overlaps with Rosemary's range (6.0–7.5), though not a perfect match.
Soil Texture
The loam soil in Alameda County is excellent for Rosemary — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is moderate (3.0%). Annual compost additions will help Rosemary.
How to Plant Rosemary
Succession Planting Rosemary
Sow every 9.1 weeks. Last sowing by Jun 15 to harvest before frost.
Plant Water Budget
Water stress score is 8/10 — 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 | 1.3" | 3" | 0" | ✅ Rainfall sufficient |
| Feb | 1.3" | 3.6" | 0" | ✅ Rainfall sufficient |
| Mar | 1.3" | 2.6" | 0" | ✅ Rainfall sufficient |
| Apr | 1.3" | 1.2" | 0.1" | 💧 Light watering |
| May | 1.3" | 0.4" | 0.9" | 🚿 Regular 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" | 0.2" | 1.1" | 🚿 Regular watering |
| Oct | 1.3" | 0.6" | 0.7" | 🚿 Regular watering |
| Nov | 1.3" | 1.5" | 0" | ✅ Rainfall sufficient |
| Dec | 1.3" | 3.1" | 0" | ✅ Rainfall sufficient |
Water needs are for active growing months only (Jan–Dec in Alameda 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 — Alameda County, CA
Rosemary Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Transplant Outdoors | January 25 | Jan 25 – Feb 8 |
| Harvest | April 19 | Apr 19 – Sep 6 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Transplant Outdoors |
| February | Transplant Outdoors |
| March | — |
| April | Harvest |
| May | Harvest |
| June | Harvest |
| July | Harvest |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.3"/week · Only during dry spells
📅 Days to Maturity
80–180 days
🧪 Soil pH
Needs 6–7.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 10a
📆 Growing Season
328 days in Alameda County
Growing Tips for Rosemary in Alameda County
Direct sow Rosemary outdoors after January 18 in Alameda County when soil has warmed and frost danger has passed.
With summer highs reaching 97°F in Alameda County, provide afternoon shade for Rosemary and water deeply in the morning.
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 Alameda County, CA?
Alameda County is in Zone 10a with an average last frost of January 18. Plan your Rosemary planting based on this frost date — see the calendar above for exact timing.
What planting zone is Alameda County, CA?
Alameda County, California is in USDA Hardiness Zone 10a. The average last spring frost is January 18 and first fall frost is December 12.
Your Alameda County Garden Planner — Free
A 24-page printable planner built for Alameda 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.