What is lawn compaction?

By | 25/11/2012
Two aeration cores

This is the first part in a series of posts I’ll be publishing about lawn aeration, detailing what aeration is, why you need to aerate your lawn, when you should aerate your lawn, how you should do it and the benefits that aeration treatments bring to your grass. Aeration is the treatment to relieve a compacted lawn, so in this first part I’m going back to the basics and have a detailed look at what lawn compaction actually is.

What is compaction?

Around half of the volume of a healthy soil is made up of gaps and channels, which allow air and moisture to pass through the soil, feeding the bacteria and other beneficial organisms that live within it. Compaction is the act of compressing this soil, reducing the amount of air and moisture that it can hold, by squeezing it together. This prevents the soil from being able to breathe.

2 Aeration cores from a lawn suffering with compaction
Two soil cores taken from a lawn on the same day.
The right one looks normal and contains plenty of moisture,
the left one is compacted and totally dry.

Why does the soil need to breathe?

Like us, the bacteria, algae, fungi, worms and other organisms that live in your soil need access to gasses and water to survive. They live within the soil, and so the soil must have a way for these organisms to access these elements.

A compacted soil is much more dense than a healthy soil. It has no space to hold moisture and air within. Consequently, the plants and animals that go to make up a healthy soil ecosystem, struggle to survive. The soil gradually “dies”.

A healthy soil is the key to a healthy lawn, so it is very important to manage how compacted your lawn is.

Clay soils do tend to compact more easily than sandy soils because the individual particles in a clay soil are much smaller than sand, so they can bind much more closely and stick together more easily.

How does a lawn become compacted?

The most common reason that a lawn becomes compacted is through use. Mowing, playing football, dogs or having a party on the lawn will all contribute to the soil particles squashing together. This problem is made worse if the soil is wet, as the air gets squeezed out more easily, and the soil will dry out without containing any air pockets.

However, even if you don’t use your lawn regularly, over time your lawn will become compacted just through the fall of rain and the effects of gravity.

How does a compacted lawn affect the grass plants?

A healthy grass plant needs a healthy root system to thrive. This enables the plant to absorb more nutrients out of the soil enable it to reach water that is deeper down. This also gives the plant great stability, it enables it to repair itself from damage more quickly, and also gives it much greater tolerance to environmental stress such as drought, as it has much more material in the roots to call upon as an emergency food or water source.

Grass that is trying to grow in compacted soil will be thin, weak, and will grow very slowly, if at all. New seed will not germinate, and the area will become thinner and weaker over time, which is far from a lush green lawn which we are all after. Weeds which thrive in compacted soil, such as greater plantain (plantago major), will tend to dominate and crowd out your grass.

If you are concerned about a compaction issue in your lawn, please don’t hesitate to get in touch and I will be happy to advise.

Kris Lord

Next time: How do I tell if my lawn is compacted and needs aerating?

Click here for more information on aeration treatments which are designed to help relieve soil compaction.

Click here to read my complete guide to soil compaction and lawn aeration.

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