When to Plant Arugula in San Juan County, WA
What to do in May
Each item below is timed to San Juan County, Washington's frost dates and soil temperatures. Skip nothing, stress about nothing.
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Start harvesting arugula
This is the payoff month. Bring a basket, bring a friend, and get into the beds.
June prep starts now
- First harvests: arugula
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.
San Juan County, Washington is in USDA Zone 9a. The average last spring frost is March 26 and the first fall frost is November 3, giving you a growing season of approximately 222 days.
At an elevation of 371 feet, San Juan County receives approximately 40.9 inches of rainfall annually with predominantly silt loam soil. Summer highs average 82°F, so choose short-season varieties of Arugula to ensure they mature before fall.
San Juan County Soil Profile
Soil Type
Silt Loam
Soil pH
5.4-6.4
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 San Juan County
How your county's soil matches Arugula's growing requirements.
Soil pH
Your soil pH (5.4–6.4) is more acidic than Arugula prefers (6.0–7.0). Add garden lime to raise pH.
Soil Texture
The silt loam soil in San Juan County is excellent for Arugula — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Arugula.
Organic Matter
Organic matter is excellent (4.8%) — Arugula will thrive.
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 Sep 14 to harvest before frost.
For a dedicated fall crop, sow by Sep 08.
Plant Water Budget
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 | — | 5.7" | 0" | ❄️ Dormant |
| Feb | — | 4.7" | 0" | ❄️ Dormant |
| Mar | 2.6" | 4.1" | 0" | ✅ Rainfall sufficient |
| Apr | 2.6" | 2.6" | 0" | ✅ Rainfall sufficient |
| May | 2.6" | 2.6" | 0" | ✅ Rainfall sufficient |
| Jun | 2.6" | 1.5" | 1.1" | 💧 Light watering |
| Jul | 2.6" | 0.6" | 2" | 🚿 Regular watering |
| Aug | 2.6" | 0.8" | 1.8" | 🚿 Regular watering |
| Sep | 2.6" | 1.8" | 0.8" | 💧 Light watering |
| Oct | 2.6" | 3.4" | 0" | ✅ Rainfall sufficient |
| Nov | 2.6" | 6.4" | 0" | ✅ Rainfall sufficient |
| Dec | — | 6.6" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Mar–Nov in San Juan 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 — San Juan County, WA
Arugula Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | February 26 | Feb 26 – Mar 12 |
| Transplant Outdoors | March 26 | Mar 26 – Apr 9 |
| Direct Sow | March 5 | Mar 5 – Mar 26 |
| Harvest | April 30 | Apr 30 – Jul 2 |
| Fall Sowing | September 8 | Sep 8 – Sep 22 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | Start Indoors |
| March | Start Indoors Transplant Outdoors Direct Sow |
| April | Transplant Outdoors Harvest |
| May | Harvest |
| June | Harvest |
| July | Harvest |
| August | — |
| September | Fall Sowing |
| October | — |
| 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_acidic
🗺️ USDA Zone
Zone 9a
📆 Growing Season
222 days in San Juan County
Growing Tips for Arugula in San Juan County
Direct sow Arugula outdoors after March 26 in San Juan County when soil has warmed and frost danger has passed.
Your generous 222.0-day season in San Juan 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
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Arugula in Other Locations
Frequently Asked Questions
When should I plant Arugula in San Juan County, WA?
San Juan County is in Zone 9a with an average last frost of March 26. Plan your Arugula planting based on this frost date — see the calendar above for exact timing.
What planting zone is San Juan County, WA?
San Juan County, Washington is in USDA Hardiness Zone 9a. The average last spring frost is March 26 and first fall frost is November 3.
Your San Juan County Garden Planner — Free
A 24-page printable planner built for San Juan County (Zone 9a). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.