Question: Compacting soil before laying lawn

By | 16/03/2018
Compacting soil and then raking it over

I received this question from a reader in March 2018.

I have an area approx. 7m x 12m which I want to make into a lawn. I need to build the ground up to a final depth of approximately 5 to 6 inches on which I will lay the turf.

How should I go about compacting soil which will be barrowed in? Could I use a roller, or should I just walk up and down?

I expect the soil will be laid in roughly 2 inch layers at a time.

Your advice would be appreciated. Thank you.

Peter

Hi Peter,

This is a great question and is fundamental in helping your lawn to look great in the future. A deep root run is the key to great grass.

Compacting soil too much and the roots will not be able to penetrate. Too little and the soil will sink, creating a lumpy lawn. So how do you get the compaction level correct?

It is important to fill in the area with the correct substrate. Compost or any material with a lot of organic matter will decompose. This is not ideal for a lawn. The area will sink and become lumpy. This happens to potted plants planted in compost. After some months the soil in a pot will sink, even though many roots have grown in the pot.

For a lawn you need a soil which is completely rotted down. Garden topsoil is ideal. I would also add a good deal of sports sand or sharp sand to the mix (up to 50/50). NOT builders sand as it can contain salts and other additives. This will aid drainage and help the soil to stay open, even when it is under compression. Ideal for a lawn. Some professional sports surfaces are 100% sand. This gives an excellent hard surface, but it is difficult to keep the grass alive in such a free draining soil. A bit extreme for the home lawn. Topsoil retains nutrients and moisture, reducing the amount of watering and feeding required.

Compacting soil

So lets say you have your soil and the area is ready to fill. I recommend filling in a couple of inches deep and then consolidating the soil. This is to remove any air gaps in the soil, but not compact it together. The best way to do this is to gently walk heel-to-heel over the area. Don’t jump or go over the same area too many times. Once this layer compacts down, barrow in more soil, rake it over and walk over it to compact it again. Repeat. For the final layer rake it smooth and level. This will avoid the terrible turf problem.

Once you have the correct level, sow your new grass seed, rake it over and water it in. This will give you a lovely level, smooth lawn with the small of sinking. The grass will take and the roots will grown downwards and stabilise the soil.

Hope this is helpful, good luck with your new lawn project.

Regards

Kris Lord
The Lawn Man

P.S. Main image is a stock photo and not from questioner.

2 thoughts on “Question: Compacting soil before laying lawn

  1. Martin

    Hi,

    I’ve kinda jumped the gun, I’ve filled my area with top soil (about 12 m2 / levelling between 100mm and 300mm – I used 1500Kg of top soil). A neighbour recommended using a wacker plate to compact the soil and help to level the area… I was planning to use the ‘garden shuffle’ to compact and level, but on trying this I’ve noticed that you can completely see where I dumped the wheel barrow loads… I clearly haven’t spread it out well… How would you suggest / recommend that I proceed from here (I put the top soil down over the weekend (sat/sun) and it’s now Tuesday Evening). Any suggestions you have would be gratefully received!

    Thanks,

    Martin

    Reply
    1. Kris Lord Post author

      Hi Martin,
      To get good levels on a lawn you just need patience and time.
      Rake it and then press it in by lightly walking on it. Then rake it again and press it in again, then rake it again and press it in again … keep doing this until a good level is achieved. It can take a long time.
      Ideally, leaving it to naturally settle will also work. Then rake down the mounds and sow your new lawn.

      NEVER use a wacker plate on soil you intend to cultivate plants in. It will completely ruin the soil structure. They are used for roads and buildings!

      Thanks for reading.

      Kris

      Reply

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