When to Plant Sweet Potatoes in Lewis County, WA
Sweet potatoes are a warm-season root crop that produces nutritious, sweet tubers in orange, white, and purple varieties. They need a long, hot growing season.
Lewis County, Washington is in USDA Zone 7b. The average last spring frost is April 25 and the first fall frost is October 24, giving you a growing season of approximately 182 days.
At an elevation of 327 feet, Lewis County receives approximately 37.3 inches of rainfall annually with predominantly silt loam soil. Summer highs average 86°F, providing good warmth for Sweet Potatoes during the growing season.
Lewis County Soil Profile
Soil Type
Silt Loam
Soil pH
5.6-6.2
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.
Plant Water Budget
Sweet Potatoes Planting Timeline — Lewis County, WA
Sweet Potatoes Planting Calendar
| Activity | When | Date Range |
|---|---|---|
| Start Indoors | March 7 | Mar 7 – Mar 21 |
| Transplant Outdoors | May 9 | May 9 – May 23 |
| Direct Sow | May 2 | May 2 – May 23 |
| Harvest | August 8 | Aug 8 – Sep 26 |
Plant 1" deep · 15" apart · Rows 24" apart
Month-by-Month Timeline
| Month | Activities |
|---|---|
| January | — |
| February | — |
| March | Start Indoors |
| April | — |
| May | Transplant Outdoors Direct Sow |
| June | — |
| July | — |
| August | Harvest |
| September | Harvest |
| October | — |
| November | — |
| December | — |
Growing Conditions
Sun
Full Sun (6-8+ hours)
Water
Moderate — regular watering
Days to Maturity
90–120 days
Soil pH
5.5 – 6.5
USDA Zone
Zone 7b
Growing Season
182 days
Growing Tips for Lewis County
Plant slips (rooted sprouts) after soil is thoroughly warm. Build raised mounds for better root development. Cure harvested roots at 80-85F for 10 days to develop sweetness.
Companion Planting
Good Companions
Avoid Planting Near
Level Up Your Garden
Sweet Potatoes in Other Locations
Frequently Asked Questions
When should I plant Sweet Potatoes in Lewis County, WA?
Lewis County is in Zone 7b with an average last frost of April 25. Plan your Sweet Potatoes planting based on this frost date — see the calendar above for exact timing.
What planting zone is Lewis County, WA?
Lewis County, Washington is in USDA Hardiness Zone 7b. The average last spring frost is April 25 and first fall frost is October 24.
Plan Your Garden with Confidence
Get our free Garden Planner — designed to help Lewis County gardeners in Zone 7b organize planting dates, track what's growing, and never miss a planting window.
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