Soil Preparation for Instant Turf

Soil preparation is by far the most important step in your instant turf project. Good preparation will provide the foundation your lawn needs to become the hard wearing, drought tolerant surface that you’re looking for.

When it comes to giving advice around soil preparation, we get lots of questions like:

• Can you establish a lawn on existing topsoil?
• What is the recommended thickness of topsoil to bring in?
• If you need to bring in some topsoil, what’s the best sort to buy?

Can you roll out turf on your existing soil?

There are some instances where you can but there are also many instances where you should not. South Australia has a very diverse mix of naturally occurring soil types ranging from coarse sands to heavy clays. I once had a property that had naturally occurring deep sandy loam in the front yard and hard-setting silty clay in the back yard. In this instance, I did not have to do anything to prepare the front yard, but the backyard needed a fair bit of work. Because of this diversity, it’s hard to come up with a “one size fits all” approach to preparing your soil for lawn. I often say to customers that there are a few things that lawns don’t like, those being

• Hard-setting soils,
• Water-repellent or non-wetting soils,
• Rocky soils where there is shallow topsoil
• The presence of remnant building materials such as paving sand and brickies sand.

Soils with these characteristics are common throughout Adelaide.  Planting in soils/materials such as these will result in unhealthy, poor-performing, high-maintenance lawns. In instances like this, I’d recommend removing and replacing a layer in order to give your lawn the best possible start (I’ll talk more about this later).  

Lawns love the following:

• Soils that drain freely
• pH-neutral soils
• Soils that don’t set hard.

There are many instances across the western, coastal suburbs where the naturally occurring soils are alluvial sandy loams and are perfect for growing lawns with little to no preparation. These include the old market garden areas from West Beach through to Outer Harbour. If your soil is not hard-setting or non-wetting, you may be able to simply remove any existing turf and plant matter, turn it over and add a thin layer of sandy loam to help you level it out.  

What is the recommended depth of topsoil to bring in?

This is a tricky question to answer! It all depends on how good your existing soil is. If you have issues similar to those mentioned above, the safe option is to bring in a 100mm layer of topsoil which may involve removing some of the existing soil. If your soil is reasonable and free of contaminants, you may be able to simply remove a 50mm layer, apply and rotary hoe in a 25mm layer of topsoil, then finish the surface off with another lighter layer of topsoil to smooth the surface off and make it easier to level.

What sort of topsoil should you buy?

Sandy Loam:

This is a question that can be answered in many different ways – lots of people have an opinion on it so I’ll tell you what we do and what works for us.  Our turf is grown down in Langhorne Creek, south of Adelaide. It grows on soil made up of nearly 80% sand, the rest being silt, loam and clay. You can buy this type of soil in most landscape supply yards and it’s called Sandy Loam.

Organic Sandy Loam:

There are other types of sandy loam around with added composts and manures which are helpful when establishing a lawn. These additives help to hold water and nutrients in the soil which in turn helps the turf establish faster, with less stress. 

You’ll have success with whichever you use.  One thing I can say is that you generally get what you pay for. Some of the cheaper ones can set hard and can be non-wetting which are ironically the two things you are trying to avoid when preparing soil for a new lawn!

To finish a soil off, your surface should be compacted, levelled and screeded till perfectly flat. Make sure you allow a 25mm gap between the finished soil height and the top of your lawn edge to allow room for the thickness of the turf roll. Click here for more information on preparing soil and installing turf

If you are unsure or want some guidance on how to prepare your soil, bring down a sample of your soil to our store in Hove, SA and we’ll give you some advice free of charge.