The Importance of Dethatching and Aerating your Lawn


Thatch is a layer of dead, organic matter which exists between the soil and the leaves of the grass plant.

The good news...

A little thatch is natural in any lawn. The right amount can actually help the grass and soil by protecting roots from heat and sun damage, whilst creating an environment for beneficial soil and surface organisms.

And the bad news...

Too much thatch can cause problems. A thick later of thatch blocks the movement of air and nutrients to the soil. Grass roots often migrate from the soil up into the thatch, where they become weak and fall victim toextreme heat or cold, as well as disease and pests. (And when roots die off, they add even more thatch to the layer!) In addition, too much thatch can exaggerate moisture problems - holding too much moisure during a wet season and repelling water during a dry season.


Very often, too much that can be traced back to well-intentioned actions on the part of the gardener. Watering, fertilising, weed and pest control are all important in moderation, however these can result in the development of excess thatch.

Here's why:

Too much growth leads to weak roots and excess lawn debris. Also, too much nitrogen can be harmful to the organisms which naturally control the build up of thatch.

Excess constant water creates a low oxygen environment that is harmful to soil organisms.

Shallow, frequent watering
This can cause roots to move up into the thatch to reach the water source. It is best to water infrequently and deeply, only when your lawn really needs it.

Herbicides and pesticides
While controlling harmful pests and weeds, using too much of these chemicals can harm the overall ecosystem in your lawn, killing off earthworms and soil microbes.


First, correct any practices listed above that may be added to the problem.

Dethatch your lawn
The best times to dethatch are late summer and early autumn. It is easiest to dethatch when the ground are grass are slightly moist. Before you dethatch, mow your lawn at a slightly lower height. It is preferrable to make at least two passes over your lawn, and even better to use a different pattern each time. After dethatching, sweep or rake up the debris. Now is a good time to fertilise lightly and water the lawn.

While dethatching removes thatch, aeration helps break down the layer of thatch. Aeration is less traumatic for your lawn and is best for controlling thatch before it gets too out of hand. (See below to learn the difference between plug and spike aerators.)

Adjust soil pH
If your soil chemistry is off, your grass will be weak and more likely to create and sufer from excess thatch. It is easy to test soil chemistry with a do-it-yourself kit from your garden centre. If you soil is too acidid, add lime; too alkaline, add sulphur. Use a drop spreader for either additive and apply according to directions.


When you aerate your lawn, you are essntially punching holes in the soil surface. This helps to loosen compacted soil and helps more air, water and nutrients to reach the roots. The best time to aerate is in the spring at the start of the growing season. Late summer or autumn aeration can also be beneficial.


A plug aerator actually pulls out small plugs of grass and soil. A spike or blade aerator cuts deep grooves int he soil. Both methods are beneficial but there are differences. Plug aerators are more disruptive and messier, but are more thorough for a lawn in need of attention. Spike aerators are less invasive, and the process lets the grass recover more quickly. These machiens are best for regular maintenance.

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