Influence of Thatch on Turf Health

The term “thatch” usually comes with negative connotations. Dethatching is a buzzword in the lawncare community. Dethatching your lawn is viewed as a badge of honor, seemingly the more aggressive a dethatching, the better. Have you ever thought about why you’re dethatching your lawn? Does it really need to be done? Or are you just dethatching because you’ve been told thatch is bad and you need to get rid of it? The truth is, that thatch isn’t inherently a bad thing, and your thatch removal efforts may not even be necessary. Fall is a common time for dethatching, especially for cool-season lawns. So, to help prepare let’s look at thatch and its effect on your lawn health.

How much thatch is too much?

Let’s get this straight right off the bat, too much thatch is a bad thing and can cause a variety of issues. But, in general, a layer of thatch measuring 0.5” or less in thickness is not detrimental to the health of your lawn. That small to moderate amount of thatch buildup can actually benefit your lawn. Thatch can provide a cushioning effect and it also makes a great home for beneficial micro- and macroorganisms present in your lawn ecosystem. Thatch also helps moderate the temperature of your grass crowns, helping mitigate the negative effects of summer heat stress, while also acting as a barrier to weed infestation and movement of pesticides into groundwater. Some consider it akin to a layer of mulch in a flower bed.

When is the best time for thatch removal? 

If you’re dealing with a layer of thatch that exceeds 0.5” in thickness, it could be time to focus on removing that thatch to benefit the vigor of your lawn. Too much thatch can result in unsightly scalping when you mow, harbor pests and pathogens, and prevent water, oxygen, fertilizer, and pesticides from reaching the soil. Proper movement of air, water, and fertilizer is essential to the well-being of your lawn. This means that the very thing weakening your turf may also be harboring the pathogens or insects that are trying to attack it. If you think that you may be experiencing some of these issues, an extensive thatch layer be to blame.   

What causes thatch accumulation?

Thatch is an accumulation of living and decomposing roots, stems, and crowns, all of which are in different stages of decomposition or life. So, naturally, over the lifespan of a lawn, some accumulation of organic matter is inevitable. Thatch is broken down into humus by earthworms and soil microorganisms. If the accumulation of decomposing organic matter is outpacing the rate at which microbes can break it down, a thatch layer will accumulate. For accumulation to outpace decomposition, excessive lawn growth or inhibition of soil microorganism activity must occur. Here are some situations which can result in one of those outcomes. 

Excessive Nitrogen Fertilization -  Nitrogen is the number one driver of plant growth. Applying too much nitrogen throughout the growing season can result in the overproduction of plant material. This can very easily exceed the rate at which plant material decomposes.

pH Imbalance - If you’re soil pH is below 6 or above 8 the microbes in your soil may be out of balance. This can result in reduced decomposition rates, leading to increased thatch accumulation.

Too Much Water - Soil microbes responsible for thatch decomposition respire aerobically, so that means they require access to oxygen. Although they require water as well, too much water impacts oxygen availability. If all the pores in the soil are filled with water, it leaves no room for oxygen. Moreover, oxygen diffusion through water is 10,000 times slower than through air.

Insecticide/Fungicide Use - Earthworms are highly beneficial to soil health as they decompose organic matter and their channels aerate the soil. Earthworms are sensitive to a select few turf pesticides. Products to avoid if concerned about earthworms include anything containing the active ingredients thiophanate-methyl, carbaryl, and trichlorfon.

Do grass clippings contributing to thatch buildup?

The short answer is no, at least not to an extent that you would benefit from bagging them over mulching. A healthy population of soil microorganisms will have no problem breaking down your grass clippings. Clippings are composed primarily of a material called cellulose, which is more easily broken down by microbes than the main constituent of the thatch layer, a material called lignin. If you’re mowing with the proper frequency, mulching your clippings rather than bagging will provide great extra nutrition for your lawn while not contributing to the thatch layer in any meaningful way. 

When should I dethatch my lawn?

For cool-season grasses, the optimum time is during the fall. The spring is an option as well, but the stress placed on the grass from thatch removal could result in a weaker stand of turf going into the heat of summer. Fall is when your cool-season lawn is growing most vigorously and is best able to repair itself from damage incurred from dethatching. Spring dethatching of cool-season lawns can also result in more weed problems compared to dethatching in the fall. For warm-season lawns, dethatching anytime from the time your lawn has fully greened up (after the last frost, as well) to the end of July, should give your grass plenty of time to recover before it’s time for it to start preparing for the rigors of a cold winter. 

Whenever you decide to dethatch, helping your lawn recover can be pretty important. Consider applying products like Simple Lawn Solutions 28-0-0, 15-0-15, or 16-4-8 after a dethatching to give your lawn the nutrition it needs to recover from any damage it sustained. For product suggestions to apply at other times of the year, consider taking our lawn quiz or contact us today for a personalized lawn care plan.