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.
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.
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.
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.