Thatch in your lawn — what it is and what you can do about It


20110125_James YoungWhat is thatch?

Like every plant, grass goes through a natural cycle of growing various parts that are later abandoned as new growth takes over. Like leaves falling from trees in autumn, the blades of grass, the runners, and the roots die off in a natural cycle throughout the year.

These dead grass parts don’t necessarily break down and go away. If the accumulation of used-up grass parts exceeds the rate of decomposition, then these dead grass parts start piling up and forming a dense mat called thatch.

New grass grows through this mat of dead growth, which can hide thatch from view. You can see thatch best at the edges of lawn; especially where grass meets pavement and the grass is mounded up and over the pavement.

Another way to check for thatch is to dig up a sample as in this picture:


A little thatch (say up to 1/2 inch) can be beneficial. It protects the soil from leaching from heavy rains, it reduces harmful temperature fluctuations, it makes the lawn springy and less likely to slip on it due to its mat-like qualities, and it cushions and protects the live grass parts when it’s being walked on.

Why Does Thatch Buildup Waste Water and Fertilizer?

The thatch layer can build from year to year and mix with the top layer of soil to form a pseudo soil layer. The thatch layer is like a sponge. It absorbs water, which sounds good at first but therein actually lies the problem.

The thatch absorbs water but it also has an extremely large surface area (all those fibers) which allows it to dry out quickly too. Thatch, being on top intercepts rain and irrigation water first, encouraging new grass roots to grow into the thatch during the dry times of year when the grass needs water the most. It’s also full of air pockets that do not hold nutrients well. The result is that roots growing in the thatch and not in the soil results in a lawn that is thirsty for water and nutrients all the time, despite watering and fertilizing regularly.

Thatch also seems to discourage deep rooting into the soil for some reason. Maybe it’s because it forms a barrier that prevents good air exchange or because it absorbs a lot of the water, encouraging roots to grow through it instead of into the soil. I don’t know for certain but the result is unhealthy grass that needs excessive water and gives you poor results for your efforts.

So if your grass gets too much thatch, say 1 inch or more, what is the solution?

Here Are Some Thatch Removal Options:
1) My favorite suggestion is to rip out the lawn altogether and grow something more deep rooted and diverse, like a mixture of trees, shrubs, and perennials. Something that gives more back while not being overly demanding of resources like grass often is.

I know some people who like their grass might feel I’m pulling a bait and switch here and they don’t want to be lectured about the ‘evils’ of grass.

However, reducing irrigation, chemical application, and lawn work is all money in your pocket and fewer headaches. It will contribute to your own personal resiliency and it really can lead to a more enjoyable way to use your yard. Additionally, vertical growth, specifically trees, have also been shown to reduce crime and boost the livability of the neighborhood as well as your house value.

This blog is about the future where gardens that waste resources will no longer be an option. This is an opportunity to choose your plants so they can provide food or be useful for crafts. They can support wildlife by providing food and nesting spaces. They can create privacy and an enclosed space that draws you in to your garden and encourages you to learn more about plant life.

2) Another suggestion is to create a “prairie lawn” of low growing perennials that reduces or eliminates mowing, is more drought tolerant, and does not require much if any imported fertility. Some nurseries sell these prairie lawn seed mixes which include low growing clovers, yarrow, daisies, and bunching grass.

They support bees and little creatures, can be walked on, provide you with wildflowers, and they often require less maintenance if grown well.

Some people, however, may not like the “messiness” of prairie lawns; they don’t give you that laser straight surface that a lawn can give you. They also have a semi-deciduous nature, so some areas may be bare in the winter.

3) A third suggestion is to pave lawn into a patio space if it’s appropriate for the area. Although paving does not do much to support the local ecology, if it reduces the mowing, thatching, fertilizing, and watering of a lawn then it very well may be better to pave some of the area with patio space instead of constantly throwing resources at it to maintain a walkable grass.

You can border your patio space with tall plantings as suggested in option 1) above. This will create a buffer with adjoining spaces, introduce plant diversity, and add more visual excitement to your garden space.

This option makes the most sense if the space is often used for outdoor activities. For example, if you find yourself wanting to use your grass space at certain times of the year, but are prevented because the grass gets soggy and muddy, then a patio surface would be a good idea.

4) Dethatch the grass. This will bring the grass back to greater health, saving you on water, fertilizer, and herbicides. Most lawn care companies offer a dethatching service or you can rent the equipment at most tool rental centers as follows:

The tool you are looking for is called a thatcher, power rake or a vertical mower. These are not to be confused with aerating machines which take plugs out of the soil to relieve compaction. An aerating machine does help somewhat by removing some thatch and poking holes to let oxygen and moisture through the thatch barrier but it doesn’t address the problem directly.

The vertical mower does a more heavy duty job for heavy thatch. It has a row of disk-like blades mounted vertically on a horizontal shaft and it slices through your lawn and thatch, cutting up anything horizontally oriented. So upright grass blades remain (up to a certain length) and horizontal thatch and grass stolons get chopped up.

The power rake and thatcher are somewhat like mechanized manual rakes. You could just rake your lawn with a hand rake but it needs to be a strong rake and it’s a lot of work for large areas.

If the thatch is really bad (let’s say more than 2 inches thick), you might think about starting over by either removing the sod or chopping it up with a tiller. A tiller chops it up and mixes it into the soil but can result in a lumpy surface that needs to be leveled. Top dress it with new soil or rake it smooth to level it or make another pass with the tiller to chop things up finer.

You can rent a sod cutter that undercuts the grass and leaves you with nice little mat strips of sod and an even surface on which to build a new lawn. However, you will have to get rid of the sod strips somewhere after you’re done sod cutting.

Consider that you could mound all that nutrient rich sod into a raised bed for growing shrubs, trees, and perennials. Top dress it with soil to even out the lumps, plant it up, and cover the open spaces with mulch: an easy new raised planting bed with its own nutrient source.

After stripping or tilling, you will need to reseed the lawn or buy new sod mats from a local supplier. Just follow the instructions on the seed bag or look to your sod supplier website for instructions on laying sod mats.

— By James Young

James Young is the owner of Blue Wheelbarrow Landscaping in Edmonds.


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