When to Plant Yam in Tillamook County, OR
Your May planting checklist for Tillamook County, Oregon
A quick May briefing for Tillamook County, Oregon gardeners — what's urgent, what's next, and what can wait.
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Get yam seeds going inside
Give them 6–8 weeks indoors before the last frost and you'll transplant into warm soil with seedlings that are already leaping.
True yams are tropical tubers distinct from sweet potatoes, producing large starchy roots that can weigh several pounds. They are a staple food in tropical regions worldwide.
Tillamook County, Oregon is in USDA Zone 9a. The average last spring frost is April 19 and the first fall frost is October 29, giving you a growing season of approximately 193 days.
At an elevation of 332 feet, Tillamook County receives approximately 40.8 inches of rainfall annually with predominantly silt loam soil. Summer highs average 85°F, providing good warmth for Yam during the growing season.
Tillamook County Soil Profile
Soil Type
Silt Loam
Soil pH
5.3-6.5
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 Tillamook County
How your county's soil matches Yam's growing requirements.
Soil pH
Your soil pH (5.3–6.5) overlaps with Yam's range (5.5–6.5), though not a perfect match.
Soil Texture
The silt loam soil in Tillamook County is excellent for Yam — good drainage, moisture retention, and nutrient holding capacity.
Organic Matter
Organic matter is excellent (5.3%) — Yam will thrive.
How to Plant Yam
Plant Water Budget
Monthly Watering Guide for Yam
Yam needs approximately 1 inches of water per week (4.3" per month). Here's how your county's rainfall compares month by month.
| Month | Yam Needs | Rainfall | You Supplement | Action |
|---|---|---|---|---|
| Jan | — | 5.4" | 0" | ❄️ Dormant |
| Feb | — | 4.1" | 0" | ❄️ Dormant |
| Mar | — | 4.1" | 0" | ❄️ Dormant |
| Apr | 4.3" | 3.4" | 0.9" | 💧 Light watering |
| May | 4.3" | 2.5" | 1.8" | 💧 Light watering |
| Jun | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Jul | 4.3" | 0.7" | 3.6" | 🚿 Regular watering |
| Aug | 4.3" | 0.8" | 3.5" | 🚿 Regular watering |
| Sep | 4.3" | 1.8" | 2.5" | 🚿 Regular watering |
| Oct | 4.3" | 3.7" | 0.6" | 💧 Light watering |
| Nov | — | 6.4" | 0" | ❄️ Dormant |
| Dec | — | 6.2" | 0" | ❄️ Dormant |
Water needs are for active growing months only (Apr–Oct in Tillamook County). Supplement amounts are based on average rainfall — actual needs vary with temperature, soil, and mulching.
Yam 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.
Yam Planting Timeline — Tillamook County, OR
Yam Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 8 | Mar 8 – Mar 22 |
| Transplant Outdoors | April 26 | Apr 26 – May 10 |
| Direct Sow | April 19 | Apr 19 – May 10 |
| Harvest | October 25 | Oct 25 – Feb 21 |
Plant 0.5" deep · 6" apart · Rows 12" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | Harvest |
| February | Harvest |
| March | Start Indoors |
| April | Transplant Outdoors Direct Sow |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | — |
| August | — |
| September | — |
| October | Harvest |
| November | Harvest |
| December | Harvest |
Growing Conditions
☀️ Sun
Full Sun (6-8+ hours)
💧 Water
1"/week · Only during dry spells
📅 Days to Maturity
180–330 days
🧪 Soil pH
Needs 5.5–6.5 · Your soil: acceptable
🗺️ USDA Zone
Zone 9a
📆 Growing Season
193 days in Tillamook County
Growing Tips for Yam in Tillamook County
Direct sow Yam outdoors after April 19 in Tillamook County when soil has warmed and frost danger has passed.
Your 193.0-day growing season in Tillamook County is tight for Yam (180.0-330.0 days to maturity). Start indoors and choose early-maturing varieties.
General growing tips
Plant tuber pieces in mounds of loose, rich soil. Provide sturdy trellising for climbing vines. Yams require a long, warm growing season of 8-11 months. Harvest when vines die back.
Companion Planting
Good Companions
Check more plant combinations with our Companion Planting Checker →
Yam in Other Locations
Frequently Asked Questions
When should I plant Yam in Tillamook County, OR?
Tillamook County is in Zone 9a with an average last frost of April 19. Plan your Yam planting based on this frost date — see the calendar above for exact timing.
What planting zone is Tillamook County, OR?
Tillamook County, Oregon is in USDA Hardiness Zone 9a. The average last spring frost is April 19 and first fall frost is October 29.
Your Tillamook County Garden Planner — Free
A 24-page printable planner built for Tillamook 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.