When to Plant Arugula in Napa County, CA
Arugula is a fast-growing cool-season green with a peppery, nutty flavor. It is excellent in salads and can be harvested as baby greens or mature leaves.
Napa County, California is in USDA Zone 9a. 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 449 feet, Napa County receives approximately 35 inches of rainfall annually with predominantly loam soil. Summer highs average 88°F, providing good warmth for Arugula during the growing season.
Napa County Soil Profile
Soil Type
Loam
Soil pH
6.7-7.5
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 Napa County
How your county's soil matches Arugula's growing requirements.
Soil pH
Your soil pH (6.7–7.5) is more alkaline than Arugula prefers (6.0–7.0). Add sulfur or peat moss to lower pH.
Soil Texture
The loam soil in Napa County is excellent for Arugula — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Arugula.
Organic Matter
Organic matter is moderate (3.0%). Annual compost additions will help Arugula.
How to Plant Arugula
Fall planting: Sow 8 weeks before your first frost date for a fall harvest.
Succession Planting Arugula
Sow every 3.4 weeks. Last sowing by Oct 07 to harvest before frost.
For a dedicated fall crop, sow by Oct 01.
Plant Water Budget
Water stress score is 6/10 — consider drought-tolerant varieties and mulching
Monthly Watering Guide for Arugula
Arugula needs approximately 0.6 inches of water per week (2.6" per month). Here's how your county's rainfall compares month by month.
| Month | Arugula Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 7.5" | 0" | ❄️ Dormant |
| Feb | 2.6" | 7.8" | 0" | ✅ Rainfall sufficient |
| Mar | 2.6" | 5.8" | 0" | ✅ Rainfall sufficient |
| Apr | 2.6" | 2.3" | 0.3" | 💧 Light watering |
| May | 2.6" | 0.8" | 1.8" | 🚿 Regular watering |
| Jun | 2.6" | 0.2" | 2.4" | 🚿 Regular watering |
| Jul | 2.6" | 0" | 2.6" | 🚿 Regular watering |
| Aug | 2.6" | 0" | 2.6" | 🚿 Regular watering |
| Sep | 2.6" | 0.3" | 2.3" | 🚿 Regular watering |
| Oct | 2.6" | 1.3" | 1.3" | 🚿 Regular watering |
| Nov | 2.6" | 3.3" | 0" | ✅ Rainfall sufficient |
| Dec | — | 5.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Feb–Nov in Napa County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Arugula 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.
Arugula Planting Timeline — Napa County, CA
Arugula 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 | April 2 | Apr 2 – Jun 4 |
| Fall Sowing | October 1 | Oct 1 – Oct 15 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Start Indoors |
| February | Start Indoors Transplant Outdoors Direct Sow |
| March | Transplant Outdoors |
| April | Harvest |
| May | Harvest |
| June | Harvest |
| July | — |
| August | — |
| September | — |
| October | Fall Sowing |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Partial Shade (3-6 hours)
💧 Water
0.6"/week · Only during dry spells
📅 Days to Maturity
30–50 days
🧪 Soil pH
Needs 6–7 · Your soil: too_alkaline
🗺️ USDA Zone
Zone 9a
📆 Growing Season
273 days in Napa County
Growing Tips for Arugula in Napa County
Direct sow Arugula outdoors after February 26 in Napa County when soil has warmed and frost danger has passed.
Your generous 274.0-day season in Napa County allows multiple plantings of Arugula. Sow every 15.0 days for continuous harvest.
Common pests for Arugula in this region include cabbage worm and flea beetles. Use row covers early in the season and inspect plants weekly.
General growing tips
Sow seeds directly every 2-3 weeks for continuous harvest. Provide afternoon shade in warm weather to prevent bolting. Harvest outer leaves first to extend production.
Companion Planting
Good Companions
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Check more plant combinations with our Companion Planting Checker →
Arugula in Other Locations
Frequently Asked Questions
When should I plant Arugula in Napa County, CA?
Napa County is in Zone 9a with an average last frost of February 26. Plan your Arugula planting based on this frost date — see the calendar above for exact timing.
What planting zone is Napa County, CA?
Napa County, California is in USDA Hardiness Zone 9a. The average last spring frost is February 26 and first fall frost is November 26.
Plan Your Garden with Confidence
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