Understanding Thatch

If you’re even a little interested in the goings on of grass, the phrase ‘thatch’ will have popped up at least once or twice. Even if you’re not all that interested in the wonderful world of turf, you might have heard about it. Quite often though, blogs and articles skim over what thatch actually is, and why you might want to keep the levels down.

Grass is a seed, and while most of the grass we see is the blades which grow up, there are also side shoots which help the grass to spread, and appear either just below or just above the surface of the soil. When the grass begins to die, so will the side shoots. A compound called lignin is found in grass plants, which means that the dead plants rot quite slowly. If the new grass is growing faster than the old grass decays, it will begin to build up. The resulting build up is known as thatch.

Not every lawn will produce thatch; it depends on the type of grass. While rye doesn’t produce any thatch, luxury lawns (you know, the ones which are really thick and lush, and require quite a lot of maintenance as it is) spread quite considerably, which means lots of organic build up.

Spotting thatch

You’ll be able to tell if there’s thatch build up if your lawn feels quite spongy underfoot. Rake the area as this could also be caused by hidden moss. Check the edges as well and you should be able to see if there is a build up of dead grass. If you there’s more than about half an inch, or you can see it on the soil surface then you probably have too much.

If you’re not sure, take a sample. Use a trowel or a bulb planted, and remove a few small pieces from several spots around your lawn. They’ll need to be at least two inches deep. The layer between your grass and the soil which is compressible and fibrous is the thatch.

Do I need to treat it?

In varying degrees this is present in all lawns, but it needs to be kept under control if you want your lawn to stay healthy. Just like not all grass is good, not all thatch is bad. Half an inch or less can actually be beneficial to your lawn. It can help to insulate against temperature extremes, and help maintain moisture levels within the soil. On a sports pitch the thatch can help provide a natural cushioned surface, which will reduce impact for those running on it.

When you have too much though, thatch can impede the drainage ability of your lawn, making it harder for water to penetrate the soil. Thatch can also harbour moss and disease. It can even stop pesticides from reaching deep enough to rid your lawn of a problem.

In drier conditions it can be difficult to get water to the roots as the thatch will trap the liquid, the soil can become hydrophobic which means it repels water and this can be difficult to overcome. Treating thatch as soon as it begins to build up is much easier, and not quite so harsh on your lawn. Because the thatch can stunt the development of the roots, the grass won’t be particularly drought resistant, so is likely to look patchy and dry as soon as the weather gets warmer.

How to remove and prevent thatch

You need to encourage the roots to grow deeply if you want to minimise thatch, and therefore you’ll need good draining. Especially in clay soil types, compaction can be a problem. Push a garden fork into the soil as deeply as you can and then give it a little wriggle. Repeat every 10cm or so across the lawn to create air channels. Using an aerator or hollow tining tool can help alleviate the problem. Use a sandy top dressing to fill the holes and allow air and water into the lawn.

If you’re feeding your grass too much fertiliser you could be doing your lawn a disservice. You’ll be speeding up the growth and there will be no time for the thatch to break down. There are different types of fertiliser for different times of the year, and the right one can make all the difference to the appearance and health of your lawn in the coming months. Start out by raking, and mowing to your desired length (remembering not to cut more than a third of the grasses height), and then you can apply your fertiliser. You won’t need as much in shady areas. If the lawn is parched, you’ll need to water the lawn before you can fertilise, or wait until a good downpour. There needs to be moisture available in the soil to make it worthwhile.