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What is Thatch and how do I remove it?

By Mark Wilton08 August 2018

Most turfgrasses are perennial plants which are always in a continuous stage of renewal. As old plants die and new grow, there will be an accumulation of organic matter which builds up in the soil.

Ideally, there should be a balance between the rate at which organic matter is produced and decomposed, generally in most situations, there is too much dead and non decayed material which has a detrimental effect on the lawn. Organic matter has value. It contains various plant nutrients which, after decomposition by microorganisms, is returned to the soil for future use by new turf grass plants.

So what is thatch?

When organic material is produced faster than can be decomposed, the turf develops an excessive amount of thatch. Thatch primarily consists of partially decomposed and some living stem and root tissue that develop in the organic layer between the base of the turf grass plant and the true soil. Stem, crown and root tissues are high in a cell wall material called lignin that is very slow to decompose. Leaves cut off in mowing are rapidly decomposed by bacteria and fungi and do not contribute to thatch. A certain amount of thatch is desirable, because it forms a cushion that increases wear tolerance in turf. When thatch accumulations go above 12mm (1/2”) however, problems usually then develop. Problems such as poor root growth, greatly reduced water movement into the soil which all lead to a lack lustre lawn. Disease and pests are also associated with heavy thatch layers.

There are many reasons for thatch build up in lawns. Improper use of water can encourage thatch development. Heavy use of chemicals is also another reason. The biggest contribution however is the excessive use of soluble nitrogen fertilisers. Nitrogen when applied too often stimulates the grass plant with high vegetative growth rates, which in turn add plant residues to the system faster than the microbes can decompose, as a result, thatch accumulates.

Checking for Thatch

A turf that has too much thatch is spongy under foot. When mowing there is a tendency for the mower to scalp areas as the machine will ‘sink’ into the turf. To estimate the depth of the thatch, use a knife or spade to take a section of the turf out, making sure that the cut goes through the thatch layer and into the soil. If the layer is more than 12mm (1/2”), then the lawn will require dethatching.

Removing Thatch

The best way to remove thatch is to use a mechanical scarifier. Set the tines on the machine so they penetrate the thatch layer to just above the soil. If the thatch is really deep, it would be wise to undertake more than one scarification, better to remove little at a time than all at once. On the golf course, course managers will verticut their greens weekly so that thatch never has a chance to build up. Applying a sand based topdressing will also help in loosening the thatch.

Author: Mark Wilton

Mark is our resident grass seed expert with over 40 years experience in the turf care industry.

What is Thatch and how do I remove it?