GROWING GUIDE
What Is a Soil Profile?
A soil profile is a vertical slice through the ground, from the surface down to weathered parent material. USDA NRCS names the usual layers A for the surface, B for the subsoil, and C for the material below. Some soils also have an organic O layer, a pale E layer, or bedrock marked R. Gardeners work the surface.
The USDA Natural Resources Conservation Service describes a soil profile as the vertical sequence of layers, called horizons. Most soils have an A horizon at the surface, a B horizon in the subsoil where materials accumulate, and a C horizon of weathered parent material. An O horizon is organic debris on the surface, common in forests and not in every garden bed. An E horizon is a pale layer that has lost minerals. R marks hard bedrock, which is not soil. A garden soil test is not a profile description. Clemson Extension says to mix cores from the surface to about 6 inches for a garden sample, and only 2 to 4 inches for a lawn. That sample is the layer you plant in. Organic-matter percent and pH are measurements of a sample, not names for the B or C horizon. Potting mix in a container has no A-B-C profile at all.
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What are the layers called?
Horizon names: O is surface organic debris, A is the mineral surface you usually garden in, E is a pale leached layer, B is subsoil, C is parent material, and R is bedrock. Most gardens do not show every letter.
| Letter | What it is | What a gardener does with it |
|---|---|---|
| O | Organic material on the surface, leaves and duff | Leave a thin layer where it belongs. It is not a potting mix. |
| A | Mineral surface, darker where organic matter has mixed in | This is the layer a garden sample and a compost top-up actually touch. |
| E | Pale subsurface that has lost minerals | Name it if you see it. Do not treat it as topsoil. |
| B | Subsoil where clay, iron, or other material has accumulated | Not the layer you are trying to turn into a 5 percent organic-matter bed. |
| C | Weathered parent material, little biological activity | Leave it. Digging it up does not create topsoil. |
| R | Hard bedrock | Not soil. |
A garden test mixes the top about 6 inches, which is the surface, not the profile. Organic-matter targets are on what organic matter is. Lime versus sulfur is the soil pH calculator. A raised bed you fill with bags is the soil calculator, and the compost you might mix in is compost at home.
Common questions
Which layer do I actually garden in?+
The surface. In many beds that is the A horizon, sometimes under a thin O layer of leaves. You are not amending the C horizon when you add an inch of compost.
Is a soil test a soil profile?+
No. Clemson’s garden sample mixes cores from the top 6 inches. That is one layer. A profile is the full sequence down to parent material or bedrock.
Does potting mix have horizons?+
No. A container is a made mix, not a soil profile. Raised-bed fill is also not an A-B-C sequence unless you left native soil in place underneath.
Where do pH and organic matter fit?+
They are lab numbers for the sample you sent, usually the surface. Use the pH calculator for lime versus sulfur, and the organic-matter guide for the percent target.
Sources & editorial notes
- USDA NRCS: a soil profile
- Clemson HGIC 1652: soil testing
- University of Maryland Extension: organic matter and soil amendments
Horizon names describe a slice of ground. They are not a potting-mix recipe. Sources checked November 6, 2026. Editorial responsibility.