When to Plant Soybeans in Spokane County, WA
Your May gardening checklist
Here's what deserves your attention in Spokane County, Washington this month. Everything below is tailored to Zone 6b and timed around your local frost dates.
-
Outdoor sowing time: soybeans
Keep the top inch of soil moist until germination — a gentle morning watering for 5–7 days does the job.
Soybeans (edamame) are a high-protein legume that fixes nitrogen in the soil. Fresh green soybeans harvested at the edamame stage are a nutritious snack.
Spokane County, Washington is in USDA Zone 6b. The average last spring frost is May 11 and the first fall frost is September 27, giving you a growing season of approximately 139 days.
At an elevation of 1,645 feet, Spokane County receives approximately 20.4 inches of rainfall annually with predominantly silt loam soil. Summer highs average 91°F, providing good warmth for Soybeans during the growing season.
Spokane County Soil Profile
Soil Type
Silt Loam
Soil pH
5.5-6.2
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 Spokane County
How your county's soil matches Soybeans's growing requirements.
Soil pH
Your soil pH (5.5–6.2) is more acidic than Soybeans prefers (6.0–7.0). Add garden lime to raise pH.
Soil Texture
The silt loam soil in Spokane County is excellent for Soybeans — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (5.4%) — Soybeans will thrive.
How to Plant Soybeans
Plant Water Budget
Monthly Watering Guide for Soybeans
Soybeans needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Soybeans Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 3.1" | 0" | ❄️ Dormant |
| Feb | — | 2.2" | 0" | ❄️ Dormant |
| Mar | — | 1.9" | 0" | ❄️ Dormant |
| Apr | — | 1.7" | 0" | ❄️ Dormant |
| May | 4.3" | 1.3" | 3" | 🚿 Regular watering |
| Jun | 4.3" | 0.8" | 3.5" | 🚿 Regular watering |
| Jul | 4.3" | 0.3" | 4" | 🚿 Regular watering |
| Aug | 4.3" | 0.4" | 3.9" | 🚿 Regular watering |
| Sep | 4.3" | 0.7" | 3.6" | 🚿 Regular watering |
| Oct | — | 1.5" | 0" | ❄️ Dormant |
| Nov | — | 3.3" | 0" | ❄️ Dormant |
| Dec | — | 3.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (May–Sep in Spokane County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Soybeans 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.
Soybeans Planting Timeline — Spokane County, WA
Soybeans Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Direct Sow | May 18 | May 18 – Jun 8 |
| Harvest | August 10 | Aug 10 – Oct 5 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | — |
| April | — |
| May | Direct Sow |
| June | Direct Sow |
| July | — |
| August | Harvest |
| September | Harvest |
| October | Harvest |
| November | — |
| December | — |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · 1-2 times/week
📅 Days to Maturity
80–120 days
🧪 Soil pH
Needs 6–7 · Your soil: too_acidic
🗺️ USDA Zone
Zone 6b
📆 Growing Season
139 days in Spokane County
Growing Tips for Soybeans in Spokane County
Direct sow Soybeans outdoors after May 11 in Spokane County when soil has warmed and frost danger has passed.
Common pests for Soybeans in this region include bean beetles and aphids. Use row covers early in the season and inspect plants weekly.
Spokane County receives only 20" of rain annually. Soybeans needs consistent moisture — install drip irrigation or water deeply 2-3 times per week.
General growing tips
Direct sow after soil warms to 60F. Plant in blocks rather than rows for better pollination. Harvest for edamame when pods are plump and bright green.
Companion Planting
Good Companions
Avoid Planting Near
Check more plant combinations with our Companion Planting Checker →
Soybeans in Other Locations
Frequently Asked Questions
When should I plant Soybeans in Spokane County, WA?
Spokane County is in Zone 6b with an average last frost of May 11. Plan your Soybeans planting based on this frost date — see the calendar above for exact timing.
What planting zone is Spokane County, WA?
Spokane County, Washington is in USDA Hardiness Zone 6b. The average last spring frost is May 11 and first fall frost is September 27.
Your Spokane County Garden Planner — Free
A 24-page printable planner built for Spokane County (Zone 6b). Planting dates, a month-by-month schedule, harvest log, seed inventory, and succession charts — all dialed in for your exact growing season.