King County, WA Extension Office & Soil Testing Directory
Welcome to the official directory resource for King County, WA. Connecting local homeowners, urban gardeners, and commercial growers with Washington's land-grant university extension resources, state soil testing lab services, and Master Gardener volunteer clinics.
1. Extension Office Contact Details & Operational Hours
The WSU Extension - King County serves as the primary educational extension center in King County. Visit or call during standard operational hours for agricultural advice, soil sample kits, and youth 4-H programs.
| Official Office Name: | WSU Extension - King County |
| Physical Address: | 1000 SW 7th St, Suite 109, Renton, WA 98057 |
| Direct Phone Desk: | (206) 263-1919 |
| Email Contact: | king.extension@wsu.edu |
| Office Hours: | Monday – Friday: 8:00 AM – 4:30 PM |
| Official Web Portal: | https://extension.wsu.edu/king/ |
2. Official Soil Testing Laboratory & Pricing
Testing your soil is the single most important step before adding fertilizers or agricultural lime. The official testing laboratory serving King County is WSU Recommended Regional Soil Testing Partner Labs.
| Official Testing Lab: | WSU Recommended Regional Soil Testing Partner Labs |
| Lab Location: | Sample submittal forms at Renton office |
| Routine Sample Fee: | $20 – $25 per sample |
| Expected Turnaround: | 5 to 7 business days |
| Official Lab Website: | https://extension.wsu.edu/soils/soil-testing/ |
How to Collect and Submit a Soil Sample in King County:
- Pick up a Soil Kit: Pick up official sample boxes and submittal forms at the WSU Extension - King County (1000 SW 7th St, Suite 109, Renton, WA 98057).
- Collect Sub-Samples: Use a clean stainless steel trowel to take 10 to 12 soil cores from a 4-to-6-inch depth across your garden or lawn area.
- Air-Dry: Mix sub-samples in a clean plastic bucket and air-dry on clean paper at room temperature (never use an oven).
- Submit Sample: Return your filled soil box to the extension office or mail directly to WSU Recommended Regional Soil Testing Partner Labs.
3. Master Gardener Volunteer Program & Plant Clinic
The Master Gardener Foundation of King County provides free plant disease diagnostics, lawn care advice, and eco-friendly pest management tips.
| Program Name: | Master Gardener Foundation of King County |
| Plant Clinic Hours: | Monday – Friday: 10:00 AM – 2:00 PM (Note: Plant clinics run seasonally; call office during winter months) |
| Direct Helpline Phone: | (206) 263-1919 |
| Program Portal: | https://mgfkc.org/ |
Volunteer Training: WSU Extension 60-hour Pacific Northwest horticulture course.
4. Regional Soil & Growing Snapshot for King County
USDA Plant Hardiness Zone: Zone 8b / 9a
Natural Soil Profile: Puget Sound Glacial Silt and Gravelly Sandy Loam
Popular Local Crops: Berries, apples, brassicas, cool-season greens, turf
Extension Specialist Tip: Pacific Northwest rainy winters leach soil nutrients; apply organic mulch and test pH every 2 years.
5. 🧮 Interactive Soil Amendment Calculator for King County
Estimate the recommended agricultural limestone or elemental sulfur needed to adjust your garden soil pH based on local Puget Sound Glacial Silt and Gravelly Sandy Loam characteristics.
📚 Recommended Extension Guides & Soil Articles
Learn more about interpreting your King County extension soil test report and managing plant nutrients:
Frequently Asked Questions (King County Directory)
The WSU Extension - King County is located at 1000 SW 7th St, Suite 109, Renton, WA 98057. You can call their main desk directly at (206) 263-1919 during standard business hours (Monday – Friday: 8:00 AM – 4:30 PM).
Standard soil analysis for King County garden samples through WSU Recommended Regional Soil Testing Partner Labs costs $20 – $25 per sample. Check with the office for special sample types.
You can reach the Master Gardener Foundation of King County hotline by calling (206) 263-1919 during plant clinic hours (Monday – Friday: 10:00 AM – 2:00 PM).
King County falls primarily within USDA Plant Hardiness Zone 8b / 9a. Local soil is characterized as Puget Sound Glacial Silt and Gravelly Sandy Loam.
Written & Verified by Sahajul
Verified Author & Founder
Sahajul is an independent agricultural data researcher based in India and founder of LocalSoilLab.com. He specializes in compiling, structuring, and verifying US land-grant university extension services, soil lab testing fee schedules, and county Master Gardener contact directories directly from official .edu and USDA NIFA portals.