St. Mary's County Soil Data
St. Mary's County, Maryland
USDA SSURGO / PHZMAvg pH
5.3
Texture
Gravelly silt loam
Drainage
Moderately well drained
Organic Matter
3.0%
Hydrologic Group
B
Data Story
About Soil in St. Mary's County, Maryland
Gravelly silt loam on the peninsula
St. Mary's County soil belongs to the Entisols order and maintains an average pH of 5.30. This pH level is almost identical to the Maryland state average of 5.31.
A gritty mix of sand and silt
The soil composition includes 49.1% sand and 35.8% silt, creating a texture known as gravelly silt loam. With 11.6% clay, the soil offers a firm structure that resists excessive erosion.
Lower organic levels require active management
Organic matter is lower here at 2.96%, compared to the 9.10% state average. The available water capacity of 0.169 in/in is slightly below the state average of 0.175 in/in, requiring careful irrigation planning.
Predictable drainage for building and farming
The soil is classified as moderately well drained and falls into Hydrologic Group B. This means it has a moderate infiltration rate, making it versatile for both agricultural use and construction.
Warm Zone 8a climate for gardening
The mild winters of Zone 8a allow for a diverse range of planting options. You can easily jumpstart your garden by adding compost to increase the relatively low organic matter levels.
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
Moderately well drained
Water is removed somewhat slowly. May have a slowly permeable layer or seasonal water table.
Soil Profile
Dominant texture: Gravelly silt loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Acidic Soil Detected
Your county's average pH is 5.3. These products help balance soil pH for healthier grass.
Browse Soil AmendmentsFrequently Asked Questions
What type of soil does St. Mary's County have?
St. Mary's County's soil is classified as Gravelly silt loam. This indicates the relative proportions of sand, silt, and clay — 49% sand, 36% silt, and 12% clay. Loamy soils hold moisture well and support a wide range of plants.
Is St. Mary's County's soil acidic or alkaline?
St. Mary's County's soil has a low pH of 5.3, which is strongly acidic. Acidic soils benefit from lime applications to raise pH and improve nutrient availability.
What is the drainage class for St. Mary's County?
St. Mary's County has a dominant drainage class of "Moderately 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. Mary's County's soil?
Based on St. Mary's County's Gravelly silt loam texture, pH of 5.3, and Moderately well drained, the soil is well suited for acid-loving plants like blueberries and azaleas, row crops and vegetable gardens, most annual and perennial crops.
What USDA soil order is found in St. Mary's County?
St. Mary's County's dominant soil order is Entisols. Entisols are recently formed soils with little to no horizon development. They are common on floodplains, steep slopes, and sandy deposits.
Soil & Planting Advisory: St. Mary's County
Soil Verdict
St. Mary's County is in USDA hardiness zone 8a, a warm climate zone. where winter lows can reach 10°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. 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.
Regional Context
St. Mary's County is somewhat warmer than the Maryland statewide average. The zone range of 7b-8a within the county means soil and planting decisions should account for local elevation and topography.
Planning your lawn? View lawn care data for St. Mary's County on LawnByCounty.com →
Other Counties in Maryland
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.