When to Plant Basil in Multnomah County, OR
This month in Multnomah County, Oregon
May is a pivotal month for Multnomah County, Oregon gardens. Focus on these tasks first and you'll set up the rest of the season for success.
-
Time to start basil inside
You're about 22 weeks out from your last frost — the perfect window to get these germinating indoors.
Before June arrives, get these ready
- First harvests: basil
Basil is a fragrant warm-season herb essential to Italian and Thai cuisines. It comes in many varieties including sweet, Thai, purple, and lemon types.
Multnomah County, Oregon is in USDA Zone 9a. The average last spring frost is April 14 and the first fall frost is October 27, giving you a growing season of approximately 196 days.
At an elevation of 357 feet, Multnomah County receives approximately 35.9 inches of rainfall annually with predominantly silt loam soil. Summer highs average 84°F, so choose short-season varieties of Basil to ensure they mature before fall.
Multnomah County Soil Profile
Soil Type
Silt Loam
Soil pH
5.8-6.3
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 Multnomah County
How your county's soil matches Basil's growing requirements.
Soil pH
Your soil pH (5.8–6.3) overlaps with Basil's range (6.0–7.0), though not a perfect match.
Soil Texture
The silt loam soil in Multnomah County is excellent for Basil — good drainage, moisture retention, and nutrient holding capacity.
Drainage
Drainage is adequate for Basil.
Organic Matter
Organic matter is excellent (4.5%) — Basil will thrive.
How to Plant Basil
Succession Planting Basil
Sow every 5.7 weeks. Last sowing by Aug 13 to harvest before frost.
Plant Water Budget
Monthly Watering Guide for Basil
Basil 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 | Basil Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 5.8" | 0" | ❄️ Dormant |
| Feb | — | 4.1" | 0" | ❄️ Dormant |
| Mar | — | 3.5" | 0" | ❄️ Dormant |
| Apr | 2.6" | 2.3" | 0.3" | 💧 Light watering |
| May | 2.6" | 2.3" | 0.3" | 💧 Light watering |
| Jun | 2.6" | 1.3" | 1.3" | 🚿 Regular watering |
| Jul | 2.6" | 0.6" | 2" | 🚿 Regular watering |
| Aug | 2.6" | 0.7" | 1.9" | 🚿 Regular watering |
| Sep | 2.6" | 1.6" | 1" | 💧 Light watering |
| Oct | 2.6" | 2.9" | 0" | ✅ Rainfall sufficient |
| Nov | — | 6" | 0" | ❄️ Dormant |
| Dec | — | 4.9" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Multnomah County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Basil 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.
Basil Planting Timeline — Multnomah County, OR
Basil Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 3 | Mar 3 – Mar 17 |
| Transplant Outdoors | April 21 | Apr 21 – May 5 |
| Direct Sow | April 21 | Apr 21 – May 12 |
| Harvest | June 16 | Jun 16 – Aug 18 |
Plant 0.5" deep · 8" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | Transplant Outdoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | Harvest |
| July | Harvest |
| August | Harvest |
| September | — |
| October | — |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
0.6"/week · Only during dry spells
📅 Days to Maturity
50–75 days
🧪 Soil pH
Needs 6–7 · Your soil: acceptable
🗺️ USDA Zone
Zone 9a
📆 Growing Season
196 days in Multnomah County
Growing Tips for Basil in Multnomah County
Direct sow Basil outdoors after April 14 in Multnomah County when soil has warmed and frost danger has passed.
General growing tips
Start seeds indoors or direct sow after last frost. Pinch flower buds to extend leaf production. Harvest leaves from the top down, cutting just above a leaf pair.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Isolate 150 ft between varieties. Different basil species can cross.
Basil in Other Locations
Frequently Asked Questions
When should I plant Basil in Multnomah County, OR?
Multnomah County is in Zone 9a with an average last frost of April 14. Plan your Basil planting based on this frost date — see the calendar above for exact timing.
What planting zone is Multnomah County, OR?
Multnomah County, Oregon is in USDA Hardiness Zone 9a. The average last spring frost is April 14 and first fall frost is October 27.
Your Multnomah County Garden Planner — Free
A 24-page printable planner built for Multnomah 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.