# When to dethatch vs aerate



## h22lude

As the title says, when do you need to dethatch vs when do you need to aerate? How can you tell you need to do one or the other, or both?


----------



## Mozart

some more questions: what time of the year is best to do each of these things?

Does dethatching disturb the pre emergent barrier if a thatching rake is used?


----------



## Delmarva Keith

For a cool season lawn, I think Fall is the best time for either or both. Both will help to reduce thatch. In Spring, anything that could possibly increase weed pressure is a definite "no."

If you have dense KBG, it will tend to produce thatch. When the thatch layer gets to around more than 1/2" might be time to think about either core aeration or power rake. Depending on the tools you have available, choose the method easiest for you.

A power rake makes a mess and produces a lot of waste to get rid of but it also gets rid of a lot of thatch fast. Core aeration completely removes a plug of thatch with the cores and if done right is plenty adequate for thinning thatch in a cool season lawn.

In addition to addressing thatch, core aeration can also help improve the soil, at least the top few inches. It loosens compaction plus if you topdress with either compost or sand, it can, over time, improve soil composition by adding what's needed for your particular soil and what you want to accomplish with it. It can take a long time (possibly thousands of years) for leaching and diffusion to move significant soil improvements deep into the subsoil but core aeration can relatively quickly address the top few inches without deep tilling up the whole lawn.

I'd think either would reduce effectiveness of a Fall preemergent if done after the app. I don't have first hand experience with that. So far, I've never been sufficiently satisfied with how things fared over the Summer to skip Fall overseed.


----------



## Delmarva Keith

Almost forgot, do not do either to any area with any bermuda infestation. The sprigs will get spread and the problem will get worse. Don't ask me how I know that


----------



## Mwhal2

Interesting, I was planning on doing both next weekend. I aerated in the spring, and I will never do that again because the crab grass got the beast of me, but that was before I found this site and plan on using a different pre emergent next spring. Not sure what though. I was always told fall is the the time to do the most work on a lawn. I was going to dethatch with a power rake, aerate, then overseed with an application of Milo, followed by another synthetic app of nitrogen a month later. Thinking of not doing the power rake, but just aerating after reading above. My lawn looks pretty good besides a few areas that I can hand thatch. Just need to get the clover and crab grass out so my new seed will take over.


----------



## Delmarva Keith

Mwhal2 said:


> Interesting, I was planning on doing both next weekend. I aerated in the spring, and I will never do that again because the crab grass got the beast of me, but that was before I found this site and plan on using a different pre emergent next spring. Not sure what though. I was always told fall is the the time to do the most work on a lawn. I was going to dethatch with a power rake, aerate, then overseed with an application of Milo, followed by another synthetic app of nitrogen a month later. Thinking of not doing the power rake, but just aerating after reading above. My lawn looks pretty good besides a few areas that I can hand thatch. Just need to get the clover and crab grass out so my new seed will take over.


 :thumbup:


----------



## TommyTester

In my opinion, core aerate now, optionally overseed, Milo now, more N a bit later.

Dethatch and rake-up in the Spring grabs all the dead crab grass and leafs. Pre-em just after that and water in.


----------



## outdoorsmen

I would dethatch and plug now. Get the thatch out cause it prevents seed to soil contact and prevents water from getting to the soil. I had a thin layer of thatch (still do) and i dont like it holding the grass seed on top. And when i pull it up by hand the dirt below it is dry, even after i watered. Yeah some may say it helps the ground from drying out, and that is true, works like a farmers no till pratice. But the difference betwwen the two is the farmer drills his seed, you broadcast the seed. So the thacth prevents seed to soil contact....unless you slit seed.


----------



## Suburban Jungle Life

Thatch is made of of the stemmy parts of the plant. Spreading grasses create thatch. KBG and warm season grasses. Fescue and rye don't contribute to thatch. If you are talking about the dead grass blades from mowing which haven't decomposed yet, that isn't thatch. It is a problem but I'm not aware of a name for that brown material which hasn't broken down yet. If you are seeding, that dead layer will prevent seed to soil contact. You will need to aerate or use a power rake to remove that material so the seeds can reach the soil.

If you have a fescue or rye lawn, they don't spread and I highly recommend seeding unless you have thick turf. You can skip the thick parts and seed the thinner parts. If you have a nomix or KBG lawn, then you may have thatch so verticutting once a year is recommended or use a core aerator or dethatcher.

Regarding whether you should power rake or core aerate, either one should be fine. Power rake will bring up all the brown material and you should rake it off or bag it with the mower. It will also loosen the top layer of soil to give you good seed to soil contact. I like to cover with peat moss but if you can keep it moist, water 4 times a day at 7am,11,3,7, then you don't need peat.

If you use a core aerator, make 2 passes and take it look at it. If you have made a good mess with the soil, that should be fine. Otherwise, do a third pass. You can leave the cores and they will eventually break down. Same process with seeding after. If you need to lime, a core aerator leaves beautiful holes for lime to get deeper in the soil. Same with adding P. These are slow to move thorough the soil profile so holes really help.

In the future, if you want, you can spray molasses to help encourage the microbes to break down that brown layer. It will take time so you will have to time it a month or two in advance and perhaps a second spray to help. This will help with thatch also but thatch, the stemmy parts, are hard to break down and will take a long time.


----------



## Mozart

I have a fairly thick KBG/tall fescue/fine fescue lawn and just put milorganite down last night.

I also have sugar maple trees in the front yard. These maples have a very shallow root system.

I'm concerned that dethatching or aerating would stress the tree out and/or damage power equipment. Is that true?

It looks like I would really benefit from dethatching though, I have quite a bit of debris around the soil and it shows through at 3" HOC. Or maybe this is the beginning of fungal disease, hope not! How do you tell the difference between diseased grass and thatch? I've been watering the mature grass 4-5x/day because I've also seeded a few areas and the irrigation is my main watering strategy. The grass looked very nice at 6" but here's what I found after mowing to 3". Any help greatly appreciated!

If fungal, what type of fungus and what treatment is best?


----------



## h22lude

So it sounds they both achieve similar results but also have their own advantages. Core aerating will help break up thatch and also help with compacted soil. Dethatching will help loosen the top layer of soil and also get the dead grass off the soil.

I have a riding mower. I'm hoping to get a tow behind aerator for this season. Might also get a dethatcher. Sounds like doing both will help with overseeding especially since I'm sure the previous owners never did either. Using a dethatcher is probably something I could do every other year and aerating do every fall.


----------



## Killsocket

I dethatched for that reason. Maybe not necessarily thatch, but the dead undecomposed stuff and have been satisfied. This is the second year with this lawn and I am sure it wasn't touched like this ever by previous owners.



Here is how much I pulled out of 2500 sq ft. Roughly 6' x 4' x 2-3' high.


I was truly shocked how much came up.


----------



## Miggity

Delmarva Keith said:


> Almost forgot, do not do either to any area with any bermuda infestation. The sprigs will get spread and the problem will get worse. Don't ask me how I know that


Same goes for Poa Triv. Don't ask me how I know that either. My back hurts, I stink and I am too dirty to step into the shower.

Side note: a power rake or slit seeder without seed set at 1/2" deep really helps rip the poa out, but is not perfect even after 8 passes. The propane asphalt torch did the rest.


----------



## Delmarva Keith

Miggity said:


> The propane asphalt torch did the rest.


 :thumbup:


----------



## TommyTester

Killsocket said:


> I dethatched for that reason. Maybe not necessarily thatch, but the dead undecomposed stuff and have been satisfied. This is the second year with this lawn and I am sure it wasn't touched like this ever by previous owners.
> 
> I was truly shocked how much came up.


Yes ... It is very satisfying to pull all that up and put it in the compost pile. It's one of the best things you can do for your lawn.


----------



## Suburban Jungle Life

TommyTester said:


> Killsocket said:
> 
> 
> 
> I dethatched for that reason. Maybe not necessarily thatch, but the dead undecomposed stuff and have been satisfied. This is the second year with this lawn and I am sure it wasn't touched like this ever by previous owners.
> 
> I was truly shocked how much came up.
> 
> 
> 
> Yes ... It is very satisfying to pull all that up and put it in the compost pile. It's one of the best things you can do for your lawn.
Click to expand...

I do this every year and it is always amazing how much comes out. On the other hand, that is lost nutrients. Have you tried spraying molasses in the summer to help break down that material? Perhaps less would come out, less work to rake or bag it, and more of it would feed your grass. You could grab some from the kitchen and spray a section in the summer to compare to the rest of the lawn when you run the dethatcher.


----------

