San Juan County Soil Data
San Juan County, Washington
USDA SSURGO / PHZMAvg pH
5.2
Texture
Loam
Drainage
N/A
Organic Matter
49.9%
Hydrologic Group
N/A
Data Story
About Soil in San Juan County, Washington
Deeply Acidic Island Soils
San Juan County features quite acidic soil with an average pH of 5.16. This is significantly lower than the national median of 6.5 and the state average of 6.20. Such acidity typically requires lime amendments for traditional vegetable gardening.
A Gritty Sandy Blend
The soil is dominated by 49.8% sand, balanced by 34.5% silt and a low 9.5% clay. This high sand content ensures easy workability and prevents the heavy compaction often seen in clay-rich areas. It offers a light, manageable texture for island farmers.
Incredible Organic Richness
This county boasts a massive 49.87% organic matter, nearly triple the state average of 14.85%. This richness translates to an available water capacity of 0.324 in/in, which is much higher than the state average of 0.194. Your plants will have excellent access to both nutrients and moisture.
Managing the Island's Water
While official drainage classes are not listed, the nearly 50% sand content suggests very rapid drainage. This is excellent for preventing root rot but means the soil can dry out quickly in the summer. Careful irrigation management is necessary during the drier months.
Island Bounty in Zone 9a
The mild Zone 9a climate and high organic content make San Juan a gardener's dream. Acid-loving plants like blueberries, rhododendrons, and camellias will thrive in this natural soil environment. Start your island garden and enjoy the benefits of this unique soil profile.
Soil Composition
Soil pH
Soil Series
Detailed soil series data not yet available for this county.
Hydrologic Group
Hydrologic group data not available.
Drainage Class
Drainage class data not available.
Soil Profile
Dominant texture: Loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Acidic Soil Detected
Your county's average pH is 5.2. These products help balance soil pH for healthier grass.
Browse Soil AmendmentsFrequently Asked Questions
What type of soil does San Juan County have?
San Juan County's soil is classified as Loam. This indicates the relative proportions of sand, silt, and clay — 50% sand, 34% silt, and 9% clay. Loamy soils hold moisture well and support a wide range of plants.
Is San Juan County's soil acidic or alkaline?
San Juan County's soil has a low pH of 5.2, which is strongly acidic. Acidic soils benefit from lime applications to raise pH and improve nutrient availability.
What is the drainage class for San Juan County?
Drainage class data is not currently available for San Juan County.
What crops or plants grow well in San Juan County's soil?
Based on San Juan County's Loam texture, pH of 5.2, and drainage class, the soil is well suited for acid-loving plants like blueberries and azaleas, row crops and vegetable gardens.
What USDA soil order is found in San Juan County?
The dominant USDA soil order for San Juan County is not currently available in our dataset.
Soil & Planting Advisory: San Juan County
Soil Verdict
San Juan County is in USDA hardiness zone 9a, a warm climate zone. where winter lows can reach 20°F. Warm winters keep soil biology active nearly year-round, accelerating decomposition but increasing pest and disease pressure in topsoil.
Planting Guidance
Tropical and subtropical plants are viable. Year-round gardening is possible, though summer heat may limit some cool-season crops. Frost is rare; tender plants can overwinter with minimal protection. Always match plant selections to the specific microclimate of your property — low spots, slopes, and wind exposure can shift effective hardiness by half a zone.
Soil Implications
Rapid organic matter turnover means soils can become nutrient-poor quickly; test annually and fertilize based on results. High soil temperatures favor certain soilborne pathogens; practice crop rotation and avoid overwatering.
Regional Context
San Juan County is significantly warmer than the Washington average, shifting effective hardiness by roughly 1.6 zones. The zone range of 8b-9a within the county means soil and planting decisions should account for local elevation and topography.
Planning your lawn? View lawn care data for San Juan County on LawnByCounty.com →
Other Counties in Washington
Soil data sourced from USDA SSURGO via Soil Data Access. Data is informational only and should not be used as a substitute for on-site soil testing. Contact your local NRCS office for site-specific soil information.