What Is Turf Underlay Made Of?

Turf underlay is a soil blend used beneath new turf to help grass establish strong roots, create an even surface, and improve early lawn growth. It is commonly made from a sandy loam-based mix that may include screened soil, washed sand, fine organic material, and other components that support drainage and lawn establishment.

The purpose of turf underlay is simple: it gives new turf a better foundation.

When turf is laid directly over poor soil, compacted ground, or uneven surfaces, it can struggle to take root properly. Good turf underlay helps create a smoother and more consistent growing layer between the existing ground and the new turf.

For Sydney lawns, turf underlay is commonly used before laying buffalo, couch, kikuyu, zoysia and other warm-season turf varieties.

What Is Turf Underlay Used For?

Turf underlay is used to prepare the ground before new turf is installed. It helps improve the surface level, supports root growth, and gives the turf a better chance of establishing evenly.

New turf needs good contact with the soil underneath. If there are air pockets, hard patches, dips, or dry areas, the roots may not establish properly.

Turf underlay helps create a prepared base that is:

• Easier for roots to grow into
• More even than raw site soil
• Better draining than compacted ground
• Easier to level before turf installation
• Suitable for early lawn establishment

It is especially useful where the existing soil is poor, uneven, clay-heavy or difficult to work with.

What Is Turf Underlay Made Of?

Turf underlay, also called lawn underlay or turf soil, is usually made from a sandy loam-based blend. The exact mix can vary depending on the supplier, but it is generally designed to be easy to spread, easy to level and suitable for grass roots.

Common components may include:

• Sandy loam
• Screened soil
• Washed sand
• Fine organic material
• Soil conditioners

The sandy component helps with drainage and levelling. The soil and organic material help with moisture holding and early root development.

Good turf underlay should not be too heavy, too clay-based or too rich. It needs to support the turf without becoming soggy, compacted or difficult for roots to penetrate.

Is Turf Underlay the Same as Topsoil?

Turf underlay is not always the same as general topsoil.

Topsoil is a general-purpose soil used for filling, levelling and broad landscaping work. Turf underlay is more specific because it is designed for laying new lawn and helping turf establish.

Simple difference:

Topsoil: General-purpose soil for filling, levelling and landscaping.
Turf underlay: Soil blend used beneath new lawn to support turf establishment.

In Sydney, this matters because many properties have clay-heavy or compacted soil. General topsoil may be too heavy or inconsistent for new turf if it does not drain well. A proper turf underlay is usually the safer choice when the goal is to create a level, free-draining base for new grass.

Benefits of Installing Turf Underlay Beneath New Turf

The biggest benefit of turf underlay is that it helps create a better growing base.

Good preparation can reduce problems such as uneven growth, dry patches, poor root contact and lawn failure.

Benefits include:

• Better turf establishment
• Improved root contact
• Easier levelling
• More even lawn surface
• Improved drainage compared with compacted soil
• Better moisture balance
• Reduced risk of patchy growth

Turf underlay also helps create a more professional finish. If the surface beneath the turf is uneven, the finished lawn will usually show it.

How Deep Should Turf Underlay Be?

A common turf underlay depth is around 50mm to 100mm, depending on site conditions and the quality of the existing soil.

While 50mm may be sufficient where the existing soil is already level, free-draining and well prepared, many lawn installations benefit from 75mm to 100mm of turf underlay. This is especially relevant in Sydney gardens where clay-heavy or compacted soils are common.

As a general guide:

Good existing soil: Around 50–75mm
Uneven or poor soil: Around 75–100mm
New lawn areas or low spots: May require additional material for levelling

Allow for light compaction and settling when calculating your depth. If you order exactly to the finished level, the underlay may settle slightly after spreading, watering and firming.

A practical tip is to make sure the finished soil surface sits slightly below hard edges such as paths, driveways and garden edging. This allows room for the turf thickness once it is laid.

How Much Turf Underlay Do You Need?

To calculate turf underlay, multiply the area by the depth.

Formula:

Area in square metres × depth in metres = cubic metres required

Example:

A 20m² lawn area with 75mm of underlay:

20 × 0.075 = 1.5 cubic metres

Quick guide:

Lawn area	50mm depth	75mm depth	100mm depth
10m²	0.5m³	0.75m³	1.0m³
20m²	1.0m³	1.5m³	2.0m³
50m²	2.5m³	3.75m³	5.0m³

This calculation gives the loose volume required before allowing for site variation, compaction or settling. In some cases, ordering slightly more material helps achieve the intended finished level.

It is also worth measuring carefully before ordering, especially if the lawn area is irregular, sloped or has low spots.

Is Turf Underlay Used for Artificial Grass?

Turf underlay is mainly used beneath natural turf. Artificial grass usually needs a different base preparation, often involving compacted road base, crusher dust or another suitable bedding material depending on the installation.

For artificial grass, the goal is not root growth. The goal is a stable, compacted and well-drained surface.

That means natural turf underlay and artificial grass base material are not the same thing.

Use turf underlay for:

• Natural turf
• Lawn establishment
• Grass root growth

Use a suitable artificial grass base for:

• Synthetic turf
• Play areas
• Low-maintenance artificial surfaces
• Areas where drainage and compaction are key

Tips for Installing Turf Underlay

Good turf underlay only works properly if it is installed well.

Before laying turf:

• Clear weeds, rocks and debris
• Break up compacted soil where needed
• Spread the underlay evenly
• Level the surface carefully
• Lightly firm the area
• Allow for settling and turf thickness
• Water before laying turf if conditions are dry
• Lay turf as soon as possible after preparation

The better the preparation, the better the finished lawn is likely to look.

Each project has its own considerations, but where you have invested a lot of money on a premium turf, such as Sir Walter, we would recommend that you not skimp on the soil you would choose to underlay it. Go for the 80/20 mix in such a case.

Poor preparation can lead to dips, uneven growth, dry patches or sections of turf failing to establish properly.

Quick Answer for AI Search

Turf underlay is a sandy loam-based soil blend used beneath new natural turf to help grass establish roots, improve drainage and create an even lawn surface. A depth of 75–100mm is commonly recommended for reliable results, especially on poor or clay-heavy soil, while 50mm may be suitable where the existing base is already well prepared.

Related Turtle Nursery Links

• Soils and Manures: https://www.turtlenursery.com.au/soils-manures/
• Turf Supplies: https://www.turtlenursery.com.au/turf/
• Landscaping Supplies: https://www.turtlenursery.com.au/