Skip to content
Grow In Backyard
Soil & Testing

Can I Use Topsoil as Fill Dirt? You Can, But It Will Settle

Topsoil compresses and shrinks as its organic matter breaks down, so anything built on it sinks. Use subsoil or hardcore for fill and save topsoil for growing.

By Zakaria 2 min read Save to Pinterest — opens Pinterest in a new tab
A worker in a hard hat laying large pipe in an excavated trench of bare earth
Photo: u_bb5pp3oyar, Pixabay Content License, via Pixabay
On this page

You can — but it will settle. Topsoil holds organic matter that keeps decomposing, so a deep layer shrinks for years and anything on it sinks. Fill dirt is low in organic matter precisely so it compacts once and stops.

Two materials, two jobs

This table answers the question on its own
Fill dirt (subsoil)Topsoil
Organic matterVery littleSubstantial
Behaviour over timeCompacts, then stableShrinks for years
Nutrients, soil lifeAlmost noneYes
Grows thingsPoorlyYes
Use forBulk fill, under structuresThe top layer
CostLowerHigher

It is a difference of behaviour, not quality.

Filling a hole properly

  1. Bulk it with subsoil or fill dirt, compacted in layers of about 15 cm. Each layer compacted before the next goes on.
  2. Finish with 10–15 cm of topsoil so grass or plants have something to root into.
  3. Mound the surface slightly proud of the surrounding ground — it will settle back.
  4. Water it in and expect to come back and top it up once.

A shallow dip in an existing lawn is different

Do not drop a thick layer on living grass — it smothers it. Use a sand and topsoil blend spread thinly, repeated over a few mowings, letting the grass grow up through each pass.

Why settlement matters

Never build on topsoil or uncompacted fill

A shed, patio, path or wall on organic-rich or loose fill will crack, tilt or sink as the ground consolidates underneath, and that failure is expensive and awkward to correct. Compact in shallow layers, use material meant for the job, and for anything structural take advice rather than guessing at depth.

Compacting in layers reduces the immediate settling. It cannot stop the shrinkage that comes from organic matter rotting away — only the choice of material does that.

Screened topsoil

Better for growing, no better for filling. Screening removes stones, roots and debris, which makes it easier to spread and nicer to plant into, but does nothing about the organic matter causing settlement — and it costs considerably more.

Going under something? Buy unscreened fill. Going on top to grow in? Screened is worth it.

Common questions

Can I use topsoil as fill dirt?

You can, and for shallow levelling in a lawn it is fine, but it is the wrong material for any fill that has to stay put. Topsoil contains organic matter that continues to decompose, so a deep layer keeps shrinking for years and anything resting on it sinks with it. Fill dirt is deliberately low in organic matter precisely because it compacts to a stable volume and then stops moving.

What is the difference between fill dirt and topsoil?

Fill dirt is subsoil taken from below the growing layer — mostly mineral particles, clay and sand with little organic matter and few nutrients. Topsoil is the upper layer that holds the organic matter, soil life and nutrients plants depend on. The practical difference is behaviour rather than quality: fill dirt compacts and stays where it is put, while topsoil settles, shrinks and grows things.

How much does topsoil settle?

Expect somewhere around ten to twenty percent of the depth over the first year or two for loose topsoil, and more where it is deep or rich in organic matter. That is why a trench backfilled with topsoil develops a visible dip, and why a raised bed filled with compost-heavy material drops noticeably in its first season. Compacting in layers reduces the immediate settling but cannot stop the shrinkage that comes from organic matter decomposing.

What should I fill a hole in the yard with?

Fill the bulk with subsoil or fill dirt compacted in layers of about 15 cm, then finish the top 10 to 15 cm with topsoil so grass or plants have something to grow in. Mound the final surface slightly above the surrounding ground because it will settle back to level. For a small dip in an existing lawn, a sand and topsoil blend spread thinly and repeated over a few mowings works better than one thick layer, which smothers the grass.

Can you build on filled ground?

Only on properly compacted fill, and never on topsoil. A shed, patio, path or wall resting on uncompacted or organic-rich fill will crack, tilt or sink as the ground beneath consolidates, and that failure is expensive and hard to correct. Fill in shallow layers with compaction between each, use material intended for the purpose, and for anything structural take advice rather than guessing at the depth.

Is screened topsoil better for filling?

It is better for growing and no better for filling. Screening removes stones, roots and debris, which makes topsoil easier to spread and more pleasant to plant into, but it does nothing about the organic matter that causes settlement and it costs considerably more. If the material is going under something, pay less for unscreened fill; if it is going on top to grow in, screened is worth it.

Backyard Weekly

Know what to plant, week by week

Join the weekly email for seasonal jobs, fixes for what is going wrong, and gear worth buying.

Not ready to subscribe? The planting calendar is free and needs no email.

By subscribing you agree to our privacy policy. Grow In Backyard will never sell your address.

Keep reading