St. Mary Parish Soil Data
St. Mary Parish, Louisiana
USDA SSURGO / PHZMAvg pH
5.9
Texture
Silty Clay Loam
Drainage
N/A
Organic Matter
20.5%
Hydrologic Group
N/A
Data Story
About Soil in St. Mary Parish, Louisiana
Robust Soils in Coastal St. Mary
St. Mary Parish boasts a soil pH of 5.95, outperforming the state average of 5.74. While still acidic compared to the national 6.5 median, these soils are chemically dynamic and highly fertile.
Dense Composition and Low Sand
This soil is remarkably heavy, containing only 5.1% sand alongside 35.9% clay and 39.8% silt. Such a low sand percentage means the soil holds water tightly, which is characteristic of the region's alluvial history.
Exceptional Organic Matter Levels
The parish features a massive 20.51% organic matter content, dwarfring the state average of 6.38%. This richness, paired with a high water capacity of 0.223 in/in, creates a powerhouse for plant growth.
Managing Water in Heavy Ground
High clay and silt levels suggest very slow drainage across the parish. Careful water management is necessary for any construction or gardening project to handle the high available water capacity.
Tropical Potential in Zone 9b
In the warm 9b zone, these nutrient-dense soils are perfect for lush tropical ornamentals and winter vegetables. With a premier soil score of 85.5, your gardening potential is among the highest in the state.
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: Silty Clay Loam
Typical soil profile. Actual depths vary by location.
USDA Soil Orders
Acidic Soil Detected
Your county's average pH is 5.9. These products help balance soil pH for healthier grass.
Browse Soil AmendmentsFrequently Asked Questions
What type of soil does St. Mary Parish have?
St. Mary Parish's soil is classified as Silty Clay Loam. This indicates the relative proportions of sand, silt, and clay — 5% sand, 40% silt, and 36% clay. Loamy soils hold moisture well and support a wide range of plants.
Is St. Mary Parish's soil acidic or alkaline?
St. Mary Parish's soil has a pH of 5.9, 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. Mary Parish?
Drainage class data is not currently available for St. Mary Parish.
What crops or plants grow well in St. Mary Parish's soil?
Based on St. Mary Parish's Silty Clay Loam texture, pH of 5.9, and drainage class, the soil is well suited for vegetables, grains, and most field crops, row crops and vegetable gardens.
What USDA soil order is found in St. Mary Parish?
The dominant USDA soil order for St. Mary Parish is not currently available in our dataset.
Soil & Planting Advisory: St. Mary Parish
Soil Verdict
St. Mary Parish is in USDA hardiness zone 9b, a warm climate zone. where winter lows can reach 25°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
St. Mary Parish closely matches the Louisiana average hardiness conditions.
Planning your lawn? View lawn care data for St. Mary Parish on LawnByCounty.com →
Other Counties in Louisiana
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.