St. Louis County Soil Data
St. Louis County, Missouri
USDA SSURGO / PHZMAvg pH
6.2
Texture
Silt loam
Drainage
Well drained
Organic Matter
3.2%
Hydrologic Group
C
Data Story
About Soil in St. Louis County, Missouri
Solid Alfisols for Suburban Growth
St. Louis County features a soil score of 64.6, almost exactly mirroring the Missouri state average. Its Alfisols have an average pH of 6.25, which is slightly more acidic than the national median but very productive.
Reliable Silt Loam Texture
The dominant texture is silt loam, composed of 61.7% silt and 19.1% clay. This high silt content makes the soil exceptionally smooth and fertile, while the 16.9% sand ensures it isn't overly heavy.
Healthy Organic Content
Organic matter stands at a healthy 3.20%, which is 60% higher than the national average. The available water capacity of 0.180 in/in is nearly identical to the state average, providing dependable moisture for landscapes.
Well Drained and Versatile
The county's soil is primarily well drained, making it ideal for a wide range of uses from farming to residential gardening. It sits in hydrologic group C, which requires some attention to runoff during extreme rain events.
A Gardener's Paradise in Zone 7a
Zone 7a provides a generous window for growing warm-weather favorites like peppers and melons. The reliable silt loam texture makes this one of the most garden-friendly counties in the state.
Soil Composition
Soil pH
Soil Series
Detailed soil series data not yet available for this county.
Hydrologic Group
Group C — Moderate-High Runoff
Soils with slow infiltration rates, often with a layer that impedes downward water movement. Higher clay content restricts drainage.
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.
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Browse Soil AmendmentsFrequently Asked Questions
What type of soil does St. Louis County have?
St. Louis County's soil is classified as Silt loam. This indicates the relative proportions of sand, silt, and clay — 17% sand, 62% silt, and 19% clay. Loamy soils hold moisture well and support a wide range of plants.
Is St. Louis County's soil acidic or alkaline?
St. Louis County's soil has a pH of 6.2, which is moderately acidic. This range suits many crops and is common across much of the eastern US.
What is the drainage class for St. Louis County?
St. Louis 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 St. Louis County's soil?
Based on St. Louis County's Silt loam texture, pH of 6.2, 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 St. Louis County?
St. Louis County's dominant soil order is Alfisols. Alfisols are moderate to high base-status soils with a clay-enriched subsoil. They support productive forests and cropland across temperate regions.
Soil & Planting Advisory: St. Louis County
Soil Verdict
St. Louis County is in USDA hardiness zone 7a, a moderate climate zone. where winter lows can reach 0°F. Mild winters mean soil rarely freezes deeply, allowing year-round microbial activity and faster organic matter breakdown.
Planting Guidance
Warm-season crops, citrus relatives, and heat-loving ornamentals do well. Cool-season vegetables should be planted in fall and winter. 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
Warm soils accelerate organic matter breakdown, so compost and mulch need replenishing more frequently than in cooler zones. Sandy soils common in warm zones drain quickly; water-retentive amendments like compost or peat help hold moisture. When soil temperatures drop below freezing, microbial nitrogen cycling stops; spring fertilization is more effective than late-fall application.
Regional Context
St. Louis County is somewhat warmer than the Missouri 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 St. Louis County on LawnByCounty.com →
Other Counties in Missouri
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.