What is lawn thatching?

Lawn thatching removes some of the above ground stems and stolons that naturally develop over time. Dethatching removes excess vegetation to rejuvenate the lawn. We dethatch the lawn with a special machine called a thatcher.


What is lawn thatch?

Turf grasses grow in various ways above ground and below ground. From our top view we see the most recently emerged grass shoots. We trim these at a uniform height with a lawn mower and call the result a lawn. What we don’t see lies below these green shoots—the stems and root systems that support the top growth. As time passes this supporting biomass typically increases in size. The type of grass matters greatly.

  • Colonial or creeping bent grasses develop above ground stems known as thatch. See The origins of lawn thatching below.
  • Red fescue and especially fine fescue can develop a thick layer of roots also called thatch.
  • Ryegrass—the most prevalent turf grass in Oregon today—does not develop thatch.
  • Kentucky bluegrass really does not thrive here, so we will skip it.

The origins of lawn thatching

Ryegrass, the most commonly cultivated lawn grass in western Oregon, does not develop thatch, so why did lawn thatching ever begin?

Well, ryegrass as a lawn grass is a relatively new entity. It came on the scene as recently as the 1970’s. Previously the native grasses—colonial bentgrass and fescue grasses were used in lawns. Sod farmers also used bluegrass, but it dies out in our climate in just a few years.

Bentgrass produces above ground stolens that gradually spread and end up looking like the end of a broom in late summer. The collective ensemble of straw-looking stolens is called thatch. Special rakes were developed to rake out the loose ends. This became known as dethatching. Machine manufacturers developed special machines with blades on a spinning shaft to reduce the manual labor.

What are the benefits of thatching my lawn?


If you have a ryegrass lawn, and you probably do, there really is no appreciable thatch to remove. However, let’s look a little further. Thatching combs out the stand of turf and removes anything not firmly attached to a grass crown.

If you look carefully after this is done, you may notice many holes in your lawn where there literally are no grass plants present. This is not good. During the growing season the grass plants tiller and develop side shoots that fill in the voids, but during periods of less turf vigor, you will see the thin areas.

What if there were a way to fill in those bare areas with new grass plants? There is. See Why overseed after thatching the lawn.


As stated in The origins of lawn thatching above, dethatching lawns came about originally for the benefit of bentgrass lawns. We have thoroughly thatched bentgrass lawns to the ground so that all you could see was dirt and stubble. It comes right back like new! However, almost certainly you do not have such a lawn, so don’t do that and don’t let anyone do it for you either! Probably there are other grasses mixed in with the bentgrass.


If over-fertilized (and this is easy to do on a fescue lawn), a thick layer of roots will develop over not that many years. Folks will call this ‘thatch’ but it in no way resembles the thatch from bentgrass. You can’t remove it with a lawn thatcher machine without also tearing out the crown of the plant. We have seen lawns devastated in this way. The only viable solution is to cut off the sod and replant with a new lawn.

The old lawn mix

If you have an older lawn that was planted say in the 60’s or earlier, the original grasses were likely a blend of fescue and bentgrass. Most likely one or the other dominated but often there will be patches of this one or that one in various areas. Weed grasses have probably come in over the years. Finally, in all likelihood someone has overseeded with ryegrass. Thatching coupled with overseeding will benefit this type of lawn.

Why overseed after thatching the lawn?

After your lawn has been dethatched, you have your one great opportunity to add back selected turf varieties into your lawn. Overseeding as it is called, is just that process. It has been used by golf courses for a long time but remains less common for smaller turf areas.

Ryegrass lacks an essential characteristic for a successful lawn. It multiplies only from seed and not vegetatively. This means that it won’t spread all by itself. In fact normal attrition of individual grass plants will decrease the plant population over time. What should you do? If you want to keep up a really nice lawn, overseed regularly!

If the lawn is aerated before thatching, the thatcher will break up the cores of soil and spread a bit of loose dirt on the surface of the lawn. This helps slightly for the new grass plants roots to grab hold of.

Adding a thin layer of mulch on top of the seed can be beneficial, especially on areas that have very little existing grass plants.

We have developed a special service that rolls all these processes up into one package.

  • Aerate the lawn with a core aerator
  • Dethatch the lawn
  • Overseed with appropriate turfgrass cultivars.
  • Mulch as needed on bare areas.

This process does not address any problems due to soil compaction, excessive shade, excessive moisture, or excessive wear from foot traffic. These may commonly be the true reason for the thinning out of the lawn.

Does your Portland, Oregon landscape need some help?