Topsoil Explained: Types, Depth, Screening and Yield

What topsoil actually is

Soil forms in layers, and the USDA Natural Resources Conservation Service names them from the top down. The O horizon is the thin skin of leaf litter and decaying plant matter. The A horizon below it is mineral soil darkened by the organic matter that has worked into it: roots, microbes, worms and everything they leave behind. Together those two are topsoil. Below them the B and C horizons are subsoil, lighter in color, lower in organic content and higher in clay, sand and rock. That is where fill dirt comes from.

The organic matter is the whole story. It is what makes topsoil hold water and nutrients and grow grass, and it is also what decomposes, compresses and settles. Put a slab on it and the slab cracks. Put sod on it and the sod lives. Our guide on fill dirt versus topsoil covers that split in detail; the short version is that topsoil goes on top of a finished grade and nowhere else.

The types of topsoil you will meet on a Texas site

Topsoil is named two ways: by what it is made of, and by what has been done to it. Both matter when you are ordering it or trying to get rid of it.

North Texas is mostly the Blackland Prairie. Its topsoil is the dark, clay-rich layer people picture when they hear the word, and it carries the same high plasticity as the subsoil beneath it, which is why it has to come off before a pad is built. West and north of Fort Worth the ground turns to sandy loam in the Cross Timbers. Houston sits on the coastal prairie, where the surface is fine silt and clay over a high water table. Our guide on expansive clay in Texas explains what the clay does under a building; the topsoil above it is the part you can put to use.

How deep topsoil runs

There is no standard depth. On undisturbed Texas ground the A horizon commonly runs 4 to 12 inches, and it is not even across a site: it collects in the low ground and the drainage ways, and it thins to almost nothing on ridges and on any ground that has been farmed, graded or built on before. A pasture that has been in grass for fifty years can carry a foot of it. A lot that was cut and filled for a previous building may have none at all.

The way to know is a test hole. Dig with a shovel or a backhoe bucket until the dark soil turns lighter and measure the dark band. Do it in three or four places, low ground and high, and average them. The NRCS Web Soil Survey lists a typical A horizon depth for every mapped soil in the state and is a good first guess, but it describes the soil as it formed, not the site as it sits today.

How many cubic yards of topsoil are in an acre

Depth times area, divided by 27. One acre is 43,560 square feet, so the table below is the whole calculation at the depths that come up most. The in-place figure is the topsoil in the ground. Once it is dug it swells about 20 percent, and the loose figure is what goes on the trucks and what you order for a delivery.

Loose figures use a 20 percent swell, weight uses 1.0 to 1.2 tons per loose cubic yard, and the load count is an 18 cubic yard end dump. Wet topsoil sits at the heavy end and can weigh out a truck before it fills it. For any other area or depth, the topsoil calculator does the arithmetic from a map outline or an acreage and counts the trucks for the rig you pick.

Why topsoil is screened

Native strip is not a finish material. It carries roots, grass, rock, clods the size of a football and whatever the site had lying on it. Screening runs it through a rotating drum or a vibrating deck with a mesh, usually somewhere between three eighths of an inch and an inch and a half, and what passes is clean, consistent topsoil that spreads flat and takes sod. What does not pass goes to the fill pile or the dumpster.

That one step is the difference between a stockpile a site pays to get rid of and a material somebody pays for. Landscape wholesalers, sod farms, golf courses and finish crews all buy screened topsoil by the yard, and they do not buy unscreened strip at any price. It is also why moisture matters: saturated black clay balls up on the screen and will not pass, so a topsoil operation waits for the pile to cure before it runs.

Topsoil on a construction site: strip, stockpile, respread or export

Mass grading starts by stripping the topsoil off the footprint, because nothing structural can sit on it. The strip is pushed into a stockpile, usually at the edge of the site, and it waits there for the rest of the job. Under the Texas construction general permit that stockpile is a regulated pile: it needs perimeter controls and it has to be stabilized when it sits idle, which on a long job means seeding or covering it.

At the close-out the site needs a topsoil cap over every finished grade that gets grass or landscaping, typically 4 to 6 inches. On most commercial sites that cap uses a fraction of what was stripped, because buildings, parking and paving cover most of the footprint. The rest is surplus. It is the same material the site paid to push into a pile, and it is worth more screened than the fill dirt around it. Our earthwork calculator treats the strip as its own stockpile, separate from the cut and fill, so you can see the surplus before the job starts.

Buying topsoil: what to specify

• Screened. Say it, and say the screen size if the plans do. Unscreened topsoil is cheaper and it is the wrong material for a finish grade.
• Depth. Sod and seed take 4 to 6 inches over a compacted grade; planting beds take more. The depth sets the volume, so settle it before you ask for a price.
• Volume in loose cubic yards. That is how it is loaded and how it is billed. Order the loose figure, not the in-place one.
• Delivery window. Topsoil is a close-out material. It should arrive when the finish crew is ready, not sit through the structural phase.

We deliver screened topsoil in commercial volumes across DFW, Austin, San Antonio and Houston, timed to the close-out. The topsoil page covers the material; the calculator above gives you the yards to put on the quote.

Getting rid of topsoil: why it can be free

Because screened topsoil has a market, a stockpile that would cost a site money to haul to a dump can instead be screened where it sits and moved out to the people who buy it. When a site has enough native topsoil, room for the screening equipment, truck access and a window of a few weeks, Soil Depot can set up on the site and take the topsoil away at no cost to the site. It clears the pile, it takes the disposal line off the budget and it takes the stockpile out of the stormwater plan.

Not every site qualifies. Small volumes, tight sites and topsoil that is mostly fill or debris do not make the arithmetic work, and those stockpiles still move as a normal export. The way to find out is to measure the pile and ask. See if your site qualifies, or run the numbers first with the topsoil calculator.