What Is “Soil”?

Soil is a dynamic natural body at or near the earth’s surface that supports—or is capable of supporting—plant growth. For soil survey work, soil is typically described to a depth of ~80 inches or to bedrock, whichever occurs first (Soil Taxonomy).

These field methods predict soil properties as defined above and may differ from how other disciplines use the term. Soil is part of the landscape; it’s examined in place, then sampled for laboratory analysis when needed. See our soil survey investigations for project workups.

What Isn’t Considered Soil?

Some materials are excluded from the definition:

• Bagged “potting soil”—not part of the earth’s surface.
• Lacustrine or marine sediments—geologic materials that may become soil if exposed.
• Excavated fill—until placed and able to support plant growth, it’s not soil. Once placed and vegetated per USDA NRCS guidance, it becomes a new soil layer.

For projects involving placed fills, see Geotechnical Engineer – Tampa.

Key Elements: Landform, Genesis, Morphology & Horizons

Landforms. Soils occur on landforms—dune swales, hillslopes, river terraces, cypress domes, and coastal flats.

Soil genesis. Soils form from parent material—ocean deposits, residuum, windblown sands or silts, alluvium, and organic accumulations. Processes include biochemical alteration, humus accumulation, and leaching/translocation by percolating rainwater.

Soil morphology. Field-observable characteristics (color, structure, redox features, etc.) help predict properties such as seasonal high water table depth.

Soil horizons. Horizons are layers roughly parallel to the surface. Some are sharply bounded; others grade gradually with depth.

The Four Components of Soil

Most soils are a mixture of minerals, organic matter, water, and gases.

Mineral Particles: Type & Size

Mineral material is the most abundant component of Florida soils; quartz is most common. For onsite wastewater and foundation decisions, particle size is usually the critical factor.

Three Mineral Sizes

• Sand (0.05–2.0 mm): visible, gritty, low chemical activity; water moves rapidly.
• Silt (0.002–0.05 mm): smooth/silky when moist; moderate activity.
• Clay (<0.002 mm): sticky when moist, high activity; slow permeability.

Sand Size Subclasses

Very coarse, coarse, medium (“sand”), fine, and very fine. In Florida, fine sand and sand are most common.

Clay & Mixed Textures

Pure silt or pure clay is uncommon; most layers are mixtures. Example: 75% sand, 10% silt, 15% clay. The mixture defines the soil texture.

Field vs. Lab Texture

Texture can be measured in the lab or estimated in the field by hand-texturing a moist sample. With practice, field estimates are acceptable for OSTDS planning.

USDA Textural Triangle & Classes

The USDA textural classification depicts 12 classes on the textural triangle.

USDA Textural Classes

Loam blends properties of sand, silt, and clay (7–27% clay, 28–50% silt, <52% sand). Other common classes: silt loam, clay loam, sandy loam, loamy sand, sandy clay loam, etc.

Common Florida Textures

Most frequent: fine sand, sand, loamy fine sand, loamy sand, fine sandy loam, sandy loam, sandy clay loam, and sandy clay. Silt-dominant textures are rare outside river floodplains and parts of far South Florida.

Soil Sampling (Quick Guide)

1. Sample undisturbed areas representative of the site; avoid fill unless it’s the design layer.
2. Record depth, color (Munsell), texture, moisture, and any redox features.
3. Bag and label by depth; maintain a simple chain of custody for lab testing when required.

Need project-specific testing? See Geotechnical Engineering – Florida or Push & Helical Piers for foundation design interfaces.

Florida Soils – FAQs

Which soil textures are most common in Florida?

Fine sand and sand dominate many landscapes; loamy fine sand and sandy loam occur where fines or organics increase.

Why does texture matter for drainage and foundations?

Texture controls permeability and bearing behavior. Sands drain fast but may lose fines; clays hold water and can shrink/swell. Designs must match texture and groundwater.

Do I need lab testing?

Field texture is often adequate for screening. Lab testing is recommended for structural design, OSTDS near limiting layers, or when permitting requires classification.