Whitman County Soil Data
Whitman County, Washington
USDA SSURGO / PHZMAvg pH
6.5
Texture
Silt loam
Drainage
Well drained
Organic Matter
6.4%
Hydrologic Group
B
Data Story
About Soil in Whitman County, Washington
Productive Mollisols of the Palouse
Whitman County features Mollisols, a highly productive soil order with a neutral pH of 6.50. This perfectly matches the national median pH, making it one of the most chemically balanced soil profiles in Washington.
The Ideal Silt Loam Mix
The soil is a classic silt loam, containing 57.6% silt and 14.6% clay. This high-silt composition creates excellent nutrient retention, while the 19.9% sand content ensures the soil remains workable for farming.
Solid Organic Foundation
The 6.42% organic matter is significantly higher than the national average of 2.0%, though it sits below the state average of 14.85%. An available water capacity of 0.183 in/in supports the county's famous dryland wheat production.
Well-Drained Agricultural Land
The soil is classified as well drained and belongs to hydrologic group B. This combination allows for efficient water movement and minimal runoff, which is ideal for both large-scale farming and home gardening.
High-Scoring Zone 6b
Whitman County sits in Hardiness Zone 6b and boasts a superior soil score of 79.0. This is a premier location to plant a resilient vegetable garden or establish hardy cereal crops.
Soil Composition
Soil pH
Soil Series
Detailed soil series data not yet available for this county.
Hydrologic Group
Group B — Moderate Runoff
Moderately deep, moderately well-drained soils with moderate infiltration rates. Good balance of drainage and water retention.
Drainage Class
Well drained
Water is removed from the soil readily but not rapidly. Optimal for most plants and construction.
Soil Profile
Dominant texture: Silt loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Soil Amendment Products
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Browse Soil AmendmentsFrequently Asked Questions
What type of soil does Whitman County have?
Whitman County's soil is classified as Silt loam. This indicates the relative proportions of sand, silt, and clay — 20% sand, 58% silt, and 15% clay. Loamy soils hold moisture well and support a wide range of plants.
Is Whitman County's soil acidic or alkaline?
Whitman County's soil has a pH of 6.5, which is near neutral. This range is ideal for most garden plants and field crops.
What is the drainage class for Whitman County?
Whitman County has a dominant drainage class of "Well drained." Well-drained soils allow excess water to move through quickly, reducing waterlogging risk and supporting most field and garden crops.
What crops or plants grow well in Whitman County's soil?
Based on Whitman County's Silt loam texture, pH of 6.5, and Well drained, the soil is well suited for vegetables, grains, and most field crops, row crops and vegetable gardens, most annual and perennial crops.
What USDA soil order is found in Whitman County?
Whitman County's dominant soil order is Mollisols. Mollisols are fertile, dark-colored soils that formed under grassland vegetation. They are among the most productive agricultural soils in the world.
Soil & Planting Advisory: Whitman County
Soil Verdict
Whitman County is in USDA hardiness zone 6b, a moderate climate zone. where winter lows can reach -5°F. Freeze-thaw cycles are moderate; soil biology slows in winter but recovers reliably in spring, supporting a broad range of plants.
Planting Guidance
A wide plant palette is possible: deciduous trees, most shrubs, cool-season vegetables, and many perennials thrive here. Winter protection (mulch, burlap wraps) helps push the zone boundary for desired species. 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
Moderate freeze-thaw cycles naturally aerate the soil but can also cause compaction in clay-heavy areas; annual core aeration is beneficial. Organic matter amendments decompose at a moderate pace — aim for 3-5% organic content for optimal fertility. When soil temperatures drop below freezing, microbial nitrogen cycling stops; spring fertilization is more effective than late-fall application.
Regional Context
Whitman County is somewhat cooler than the Washington statewide average. The zone range of 6b-7a within the county means soil and planting decisions should account for local elevation and topography.
Planning your lawn? View lawn care data for Whitman 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.