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10.2 Soil for lawns

Topsoil for a new lawn from seed or sod, and topdressing to even out an old one.

Cross-section of a new lawn: existing subsoil loosened on top, the first 50 mm of new topsoil mixed into it, then topsoil to 150 mm in total, with grass on top. 150 mm 1 Existing subsoil loosened on top 2 Mixed zone first 50 mm dug in 3 Topsoil loam or sandy loam 4 Grass seed or sod
Cross-section of a new lawn on 150 mm of topsoil.

At a glance

Difficulty
2 of 4
Time
1 day per 50 m², with a wheelbarrow
Tools
Spade, garden fork or rotary tiller, wheelbarrow, landscape rake, lawn roller, pegs and string
Parts
  1. 1  Existing subsoil, loosened
  2. 2  Mixed zone
  3. 3  Topsoil
  4. 4  Seed or sod

What you need per m², 150 mm topsoil

MaterialKindTypeAmount
Topsoil Loam or sandy loam Screened, free of roots, stones and weeds 0.15 m³
or Loam or sandy loam 100 mm if topsoil is hard to get: the minimum 0.10 m³
Topdressing Same as the lawn soil For an existing lawn, per application 0.012 m³

Why 150 mm of loam?

150 mm

Lawns grow best on at least 150 mm of well-drained topsoil. 100 mm is the least to aim for.

Loam

Lawn guides ask for a sandy loam to loam: a soil with a fair mix of sand, silt and clay (10.6 shows how to check yours).

Mix the first layer

New soil laid straight on old makes a boundary that water stalls at. Dig the first 50 mm into the ground below.

pH 6–7

Most lawn grasses like slightly acid soil. The best range depends on the grass, so test before you lime (10.6).

Step by step

  1. 1

    Clear and loosen the ground.

    Remove stones, roots, rubble and old sod. Loosen the top of the existing soil with a fork or tiller so the new soil can bond to it.

    Loosened ground, rubble removed
  2. 2

    Spread the first 50 mm and mix it in.

    Spread about 50 mm of topsoil and dig or till it into the soil below. This blends the two soils so water and roots pass through.

    First layer tilled into the ground
  3. 3

    Spread the rest to full depth.

    Add topsoil until it is 150 mm deep in total, or at least 100 mm. Rake it level against pegs, with the surface sloping gently away from buildings (10.1).

    Topsoil raked to the pegs
  4. 4

    Firm it with a roller.

    Roll the area to firm and smooth it. If your footprints sink more than 25 mm, roll again. Fill the dips that show with more topsoil.

    Lawn roller on the topsoil
  5. 5

    Rake fine and sow or lay sod.

    Rake the top into a fine, crumbly surface. Sow seed or lay sod straight away, and keep it moist until it has rooted.

    Sod laid on the finished seedbed
  6. 6

    Old lawn: topdress thinly.

    To even out bumps or improve an existing lawn, spread no more than 12 mm at a time and brush it in so the grass shows through. Repeat lightly rather than adding a thick layer; 10.7 has the details.

    Thin topdressing brushed into the grass
Specifications
PartKindThicknessNote
TopsoilSandy loam to loam150 mm (min. 100 mm)Idaho: at least 100–150 mm. Connecticut and Kentucky: 150 mm.
Mixed zoneNew + old soilfirst 50 mmKentucky. Connecticut mixes half the new soil in.
AmendmentsCompost, limeinto top 150–200 mmCornell Cooperative Extension Nassau.
pH–about 6–7Kentucky bluegrass 6.0–7.0, tall fescue 5.5–6.5 (UGA); 6.3–6.8 (Cornell CE Nassau).
TopdressingLike the lawn soilmax 12 mm at a timeClemson: light and frequent.

Amount

1 m² × 100 mm = 0.1 m³. A Tennessee guide gives 12½ cubic yards for a 100 mm layer on 1,000 ft², which is the same 0.1 m³ per m².

Firmness

Roll before sowing. Footprints deeper than 25 mm mean the soil needs more rolling or dragging.

Sources

  1. University of Idaho Extension CIS 1062, Starting a home lawn: topsoil at least 100–150 mm (4–6 in) deep; sandy loam to loam preferred
  2. Connecticut Agricultural Experiment Station, Topsoil for the home landscape: lawns grow best on at least 150 mm (6 in) of well-drained topsoil; mix half of the new soil with the existing soil to avoid an interface that blocks water
  3. Penn State Extension, Lawn establishment: rough grading on the subsoil before the topsoil goes back; at least 100–150 mm (4–6 in) of topsoil, measured firmed or settled
  4. University of Kentucky AGR-203: ideally 150 mm (6 in) of topsoil; mix the first 50 mm (2 in) into the existing soil to avoid an abrupt change in texture
  5. University of Tennessee W160-A: fertile loam soil; fine grade and roll; roll again if footprints are deeper than 25 mm (1 in); 12½ yd³ of topsoil per 1,000 ft² for a 100 mm (4 in) layer
  6. University of Georgia C1058-1, Turfgrass fertility, soil texture, organic matter, aeration and pH: most turfgrasses grow best in slightly acid soil; Kentucky bluegrass 6.0–7.0, tall fescue 5.5–6.5
  7. Cornell Cooperative Extension Nassau County, Building a new lawn: lawn grasses prefer pH 6.3–6.8; mix amendments into the top 150–200 mm (6–8 in)
  8. Clemson University HGIC, Topdressing a home lawn: no more than 12 mm (½ in) at a time; light and frequent applications; sand only where the native soil is sandy

Inches converted at 1 in = 25.4 mm and rounded. Imperial amounts are per 10 ft².

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