Topsoil vs. Fill Dirt
Topsoil is the screened, nutrient-rich upper layer of soil used to grow lawns, gardens, and plants. Fill dirt is cheaper subsoil, mostly clay, sand, and rock with little organic matter, used to raise grade, backfill, or build a stable base. In short: topsoil grows things, fill dirt supports things.
What topsoil is
Topsoil is the top few inches of the earth’s surface, where organic matter, microbes, and nutrients concentrate. For sale it is usually screened to remove rocks, roots, and debris, and it may be graded as “screened,” “premium,” or “garden blend” depending on how fine it is and whether compost is mixed in. Because it holds moisture and feeds roots, topsoil is what you spread before laying sod, seeding a lawn, or filling raised garden beds.
What fill dirt is
Fill dirt comes from below the topsoil layer: subsoil made mostly of clay, sand, silt, and rock, with the organic material screened out or naturally absent. Without organic matter it does not decompose or settle much over time, which is exactly what you want under a structure. It is the cheapest bulk soil product because it is essentially raw earth moved from an excavation site.
When to use each
- Use topsoil for the final growing layer: new lawns, gardens, flower beds, leveling low spots you plan to plant, and top-dressing.
- Use fill dirt to build up grade, backfill around foundations, raise a low yard, fill in a pool or pond, or create a compacted base beneath patios and driveways.
A common approach on regrading jobs is to bring in fill dirt for the bulk of the volume, then cap it with several inches of topsoil so grass and plants can take root.
Buying and pricing considerations
Related terms
Frequently asked questions
Can I plant grass in fill dirt?+
Not well. Fill dirt lacks the organic matter and nutrients grass needs. Spread several inches of topsoil over compacted fill dirt first, then seed or sod.
Is fill dirt cheaper than topsoil?+
Yes. Fill dirt is raw subsoil with no screening or organic content, so it is typically the least expensive bulk soil a yard sells, while screened topsoil commands a premium.
How much topsoil do I need over fill dirt?+
For a new lawn, 4 to 6 inches of quality topsoil over the fill is a common target; garden beds often want more. Use a soil calculator to convert your area and depth to cubic yards.