The Q&A Archives: How do I dethatch my lawn?

Question: Too much for me to rake (3/4 acre); I am a senior, limited strength. Is their a

Answer: Thatch buildup and soil compaction are conditions that cause lawns to struggle. When severe, they can ruin a lawn. Luckily, both problems can be resolved. Simply dethatching or aerating the lawn will provide an immediate fix, but it is also important to find out what the contributing factors are and make some changes so that the solution will be long-term, not just temporary.

Thatch is a layer of debris, made up mostly of grass clippings, that accumulates above the soil and below the blades of grass. This isn't just a layer of freshly cut grass clippings. To see it clearly, simply dig out a scoop of your lawn (don't worry, you can put it right back when you're done) and look at it from the side. You should be able to identify the soil, the thatch and the top growth of the lawn grasses. The thatch layer will look like a tightly knit layer of brown debris. While thatch is primarily composed of cut grass blades, it also contains the bits and pieces of leaves and twigs that have fallen onto the lawn. In a healthy lawn, the thatch layer will decay naturally, providing nutrients for the lawn. A healthy lawn will have a layer of thatch about a half inch thick. Having no thatch layer isn't the goal either, because that can open the lawn to drought and heat stress. Thatch not only provides nutrients, it also helps shade and protect the crowns of the grass plants and helps conserve moisture. Lawns with a healthy layer of thatch do not need dethatching.

Sometimes the lawn can have too much thatch. Excessive thatch happens when the lawn is fertilized too often, the grass clippings are too long, or there aren't enough of the microorganisms that digest the thatch present. Most often, it is a combination of these factors. When the thatch layer is too deep (in excess of a half inch), the lawn will begin to thin. Lawns with heavy thatch tend to have a shallow root system, making it harder to maintain the grass. Thatch can keep water, air and nutrients from getting to the roots. Also, lawns with excessive thatch are more likely to have problems with diseases.

Dethatching removes excess thatch. It is best to dethatch the varieties of grass grown in our area in early fall. (When lawns are dethatched in spring, there is a much greater risk of damaging the newly awakening grass crowns.) If a severe thatch problem is discovered in spring, you are faced with deciding if more damage will be done by dethatching in spring or by leaving the thatch on the lawn for the summer. When it is time to dethatch, mowing the lawn fairly low just before starting will make the job easier. If you are up to it, in small areas remove thatch by raking back and forth. Hand raking is a backbreaking way of removing thatch from any but the smallest areas. There are several better ways to accomplish this task. If the thatch isn't so severe that it is smothering the crowns of the grass plants (over an inch deep), consider using a core aerator to solve the problem. The cores of soil will pull up the microorganisms needed to digest excess thatch naturally, turning it into nutrients for the lawn. For a more serious thatch problem, there are mechanical dethatchers. These machines are usually rented for the day or many lawn care companies offer this service.

Plant roots need air in the soil and good drainage. In their absence, root systems will be shallow and weak. In lawns, signs of compacted soil include poor drainage (puddling), excessive weeds despite the use of good weed controls and poor grass growth despite good maintenance practices. When the soil is compacted, nutrients and water are slow to get to the roots, further weakening the plants. Soil compaction is a problem in high traffic areas or where heavy equipment has been used for construction, grading or even mowing. If you don't know if your soil is compacted, you can check it out yourself. Take a sharp shovel into the lawn and try to dig out a scoop of turf and the underlying soil. If it isn't a struggle to sink the shovel in at least half way, your soil isn't too compacted. Look at the sample you removed. There are probably lots of grass roots that extend 4-6 inches below the surface. You will be able to see spaces in the soil between the particles and it will crumble fairly easily. If you have to jump up and down on the shovel to get it into the soil, you have a problem! Look at the sample you removed. There probably won't be a deep, extensive root system for the grass. It will also look fairly solid and will be hard to break up. This soil needs aeration.

Aeration is best done in late summer or early fall. Mechanical core or plug aerators are the only good way to aerate a lawn. They pull up a core of soil and leave it on the surface. Core aerators can be rented, or many lawn care companies offer this service. These machines should pull out plugs that are about the size of your little finger. It may sound like too many holes, but the aerator should be run back and forth until there are 20-40 holes in every square foot. The holes allow for air, rain and nutrients to penetrate the soil better. It also gives the roots room to grow. The lawn will look rough for a few weeks, but this is the right amount. Leave the cores on the surface to dissolve over the next few weeks. The soil in the cores contains millions of microorganisms that help digest thatch naturally, creating a healthier lawn.

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