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Question DetailsAsked on 9/26/2013

what does a dethaching lawn mower do to the yard

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4 Answers


Thatch is the dead grass cuttings that accumulates in your lawn, especially in colder climates where it does not biodegrade in the course of a shorter summer. Eventually, the mat gets thick enough that most of your lawn's root mass is in the thatch rather than the dirt, which makes your lawn more susceptible to drought and winter kill, plus provides a prime environment for moss growth and root-burrowing bugs.

A dethatcher mower, or a thatching blade for your lawnmower, digs this thatch out with either rotting teeth or blades, or for the mower attachment blades, uses sharp springs on the end of the blade. You normally thatch in the spring when the grass is dormant and about to start growing (as a lot of the roots are cut). You end up with a lot of dead grass cuttings on the surface afterwards that you need to rack up, but makes great material for your mulch pile if you have one.

You can have a lawn care company do it for you, or do it yourself with a special blade and spring attachments that mounts on your mower in place of your normal cutting blade. Note - buy several sets of springs - my ground is pretty rocky under the grass, and goes through two pairs of springs to do one thatching pass on about 4500sf of lawn. (The springs wear out because the end abrade away).

In some areas not needed at all, and can really tear up lawn in real sandy soils or with short, shallow growth like zoysia and kentucky bluegrass if done too aggressively, whereas in other areas like with tall fescue it might have to be done every 5 years or so. Generally, if your lawn is beginning to feel like a spongy mat or like shag carpet when you mow, it might need it - google for lawn care articles for more detail, and on the benefits of thatching and plug coring aeration, which is the other major lawn care mode, to aerate your lawn.

Answered 6 years ago by LCD


I came back to this question much later as a possible reference for a similar question - noticed in 2nd paragraph it says "rotting teeth or blades" - obviously should be "rotating" teeth or blades.

Answered 6 years ago by LCD


Damages the root system,much better off core aerating

Answered 5 years ago by kstreett


kstreett - core aeration is a different thing entirely. Thatching removes the dead grass that accumulates in high grass growth or low biodegradation zones where the cuttings do not decay as fast as they form so you get a thick springy mat of dead grass cuttings. This promotes moss growth, and also causes much of the root zone to grow in the thatch rather than in the "dirt" as the zone gets thicker - hence making the grass more susceptible to physical damage and to drought and insect damage, as well as providing a ready zone for the stem and root-eating bugs like cinch bugs and others to live in. Thatching does cut some roots, and if it is real bad you will tear out some actual divots or clumps of grass - but those are just a symptom that you have a thatch problem. The cut roots are only cut at the top of the root zone, and if done properly only a certain percentage are cut and the cut roots regrow at both sides ofthe cut, promoting MORE and healthier root growth and a denser grass growth.

Core aeration is intended to loosen the soil in the rooting zone and works by removing a plug of soil from the ground - also cutting and actually removing some of the roots along the way, but is intended (like all aeration) to loosen up the packed soil and provide open space and looser, less dense soil to promote air access and water penetration and drainage without getting saturated. Spiked roller aeration actually does a better job of slicing into and opening the soil without leaving the relatively large aeration hole which locally kills the grass and can cause ponding, BUT it works by further compacting the soil around the hole or slice, which is bad - so core aeration is the lesser of evils. Would be ideal if a smaller core tube could be developed to reduce the size of plug reduced, but that will take some more technology so for now 1/4" or so plugs are what one is stuck with, and a smaller tube diameter would only work in fine sand or clay due to blocking of the tubes with coarse sand or gravel, so you have what you have to work with.

Both are valid lawn care measures, but for different purposes, typically a lawn will need them at different intervals, and in many areas and/or types of grass thatching is not needed at all. Or made much less frequent by bagging the cuttings rather than letting them lie - though that then removes those nutrients from the lawn so they have to be replaced (in all but the richest soils) by fertilizing - making for a viscous cycle and also killing more of the beneficial microbes and insects in the lawn, which tends to make it more sterile and hence more susceptible to drought or winterkill and weed growth.

Answered 4 years ago by LCD

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