Find out why dead and dying grass in your lawn could be a sign that the lawn is suffocating. Learn what thatch is and why it can be a problem, and get step-by-step instructions for how to de-thatch a lawn.
LESLIE: Well, if you’ve spotted a lot of dead or dying grass in your lawn , it could be a sign that your lawn is suffocating.
TOM: That’s right. And the culprit could be the thatch that’s keeping your lawn’s roots from getting what it needs. Roger Cook  is the landscape contractor for TV’s This Old House  and joins us now with some tips.
ROGER: Hey, thanks for having me here.
TOM: So let’s define exactly what thatch is. It’s not a good thing, is it?
ROGER: No, thatch is a layer that builds up on top of the soil where the bottom blades of the grass are. And it’s made up of all the organic material that breaks down and falls in there. And as that layer builds up over time, it can stop air, water and even fertilizer  from getting down into the roots themselves.
TOM: So, it really seals off those roots from what it needs to grow.
ROGER: Think of it as an impervious layer in the soil. And it’s caused by getting thicker and thicker and thicker declining grass.
LESLIE: But I mean that’s all naturally occurring, so you would think that it could be a good thing because it’s happening from leaves that fall down and the grass dying on its own, correct?
ROGER: Right. But we’re not going to tolerate a lawn that comes and goes as it wants. We want it green and we want it now.
LESLIE: Mm-hmm. Well, we’re Americans, dang it.
TOM: So darn it, let’s get it. So how do we get rid of that thatch and how often do we have to do this? Is this a yearly thing?
ROGER: Well, the process is called "dethatching."
ROGER: So that’s a way you go in and you mechanically remove the thatch. And there’s a couple of different ways to do it. I usually do it early in the spring and that way, we get a whole growing season in without having any problem.
LESLIE: Do you find that you get more buildup of it over the winter months?
ROGER: No, not at all. It’s something that happens periodically during the year. It just builds up. And the reason we do it in the spring is where – they’re raking the lawn anyway.
ROGER: So this goes in combination with raking.
Now, you could take a really stiff rake and work really hard and pull it out in a small area. They also make a dethatching rake. It has a bunch of almost C-shaped blades on it.
ROGER: And you try pulling that through a lawn for an hour or so and you’ll have bulging biceps. So we use a machine. Has a bunch of steel blades on it. It’s probably 18 to 24 inches wide. And you go over the lawn and it literally cuts and pulls up all that grass. And when you do it, you’ll be amazed at how much brown stuff you pull out. So it’s pulling out dead grass  and it’s pulling out the thatch and it’s opening the lawn up for the spring.
TOM: Now, once you do have it open, is that a really good time to add fertilizer?
ROGER: It’s a great time to add fertilizer. And usually because it’s in the spring – if you have a crabgrass problem, though – you’ve had it in the past – and on those certain areas, it’s a great time to add a crabgrass preventer.
LESLIE: Is there anything useful that you can do with the thatch? Can you turn around and use that for compost ? Can you use it for mulching?
ROGER: We use it for compost; we add it to our mix. But if it’s had chemicals on it, you want to make sure that that compost doesn’t go into gardens.
ROGER: So any – we want to separate that from the garden compost.
TOM: Now, is there any time that you don’t want to thatch? Maybe in a drought or something like that?
ROGER: No. Any time after the initial spring. Because what happens is you’re opening up that lawn and when you open up a lawn, the weed seeds love it. The crabgrass will go crazy, the dandelions – everything will get into that lawn.
ROGER: If you thatch mid-summer on, you’ll be in trouble.
TOM: So timing is critical but it’s a very important thing to get done once a year.
ROGER: Yeah, it’s – we think of it as raking the lawn. Or thatching the lawn is like waking it up for spring.
TOM: Good advice. Roger Cook, the landscape contractor on TV’s This Old House, thanks so much for stopping by The Money Pit.
ROGER: Oh, just call me Dr. Thatch.
LESLIE: Alright. You can catch the current season of This Old House and Ask This Old House on PBS. For local listings and step-by-step videos of many common home improvement projects, visit ThisOldHouse.com.
TOM: And This Old House and Ask This Old House are brought to you by The Home Depot. The Home Depot, more saving, more doing.