Composting grass clippings treated by a lawn care company

Hi everyone, we moved into our new place with five acres last November. By the lack of dandelions and other lawn weeds, it's pretty obvious the previous owners had the law treated with something. The neighbor across the street confirmed. Obviously I won't be doing that.

How long until it is safe to add our grass clippings to a compost pile? I plan to use the compost in the vegetable garden. Months? Years? Decades?

I don't know what specifically was applied, but I can probably try to find out if it matters.

Thanks.

Yes, it does matter. I cannot remember the chemicals but some of them are persistent for years. This is even after being digested by animals!

I'm aware of a very different lawn culture in the USA.
I'd be checking out clopyralid and it's nasty systemic 'relatives'.
These are the main culprits in the poisoned compost nightmares, and probably what I'd be asking the lawn guys about.
as far as I know commercial operators in many states are still allowed to use them, while they're illegal for domestic use
While other herbicides are nasty, they don't generally persist obviously in the soil and plant material, as these do.
I couldn't for the life of me find good references about how long to wait after the last application before beginning to use plant matter with this class of poisons: all the info I found was about times to leave actual compost.
I do know you can get lab tests for herbicides, but I imagine it's not cheap...
a great opportunity to get a soil test if you haven't, and it's your 'thing' (I think lab soil tests are awesome!)
*edited*
for bad spelling and explanation

This depends on your definition of safe. Will it kill you to compost those grass clippings and use them on your veggies? Nope. Is it an ideal situation? Nope. Is using that compost on to grow your own veggies better than what you are going to buy in the store? Absolutely. And every year it will get better. The best way to break down those chemicals is through the fungal process, so compost, compost, compost and it will get better. I've seen data that suggests that composting can reduce many herbicides by 80%. And if you are mixing in leaves and other "browns" into you compost that haven't been treated, you'll be reducing your exposure even more. You are beginning the process of healing the land and in the start, it isn't ideal, but the food you grow will be better than what most people in this world are eating so I wouldn't worry too much about it. And in 3-5 years you'll be approaching only trace amounts of chemicals left and the skills you will have gained by getting started sooner rather than later will be extremely valuable.

Tom, I agree with you up to a point, but unfortunately the herbicides I referenced can have some extremely long-term, devastating effects on plant growth.

The mechanism of composting creates complex long chain carbon molecules. These will lock up the toxins in their structure. Once captured, the toxin becomes inert even if they have a very long "shelf" life.

So, what happens to them once they are taken up into the plant and broken down again? THAT is my concern. Same concern for composting GMO plant material.

They aren't taken up. They are locked in the humus

How do you explain the example in the first post, for which there is substantial evidence that the chemicals remain active for several years. Why don't they compost in place in the ground? Why do they remain persistent even when put through a digestion process?

The composting mechanism operates at a very low level, if at all, in top soil typical of an urban landscape.

For example, in my neighbourhood, buried branches and sticks from the original development come to the surface or are uncovered by earthworks years later. They just don't break down because the soil organisms have been so completely degraded.

In this situation, I'm not at all surprised that these chemicals remain in the soil for a long time.

A compost heap is a completely different environment.

The first thing I would do is find out exactly what was used when and how often, then research those particular herbicides. I am always careful with my compost ingredients...I don't put in anything that I can't identify all of it's parts...so for me that means no paper/cardboard of any kind and certainly no herbicide treated grass clippings. I would never be confident enough to believe that composting will tie up all toxins. I guess If it were me I might mow and let the clippings fall in place and just not consider them a resource.

I'm tempted to remove this thread because I want these forums to not talk about pesticides or GMOs.

I suppose that as long as the focus is to explore how to move a piece of land away from a problem and toward permaculture, then it can remain.

A few important points:

1) hundreds of composting operations have gone out of business because they could not come up with a composting process to get the persistent herbicides out. So while composting will break down a lot of icky things, persistent herbicides is not one of them.

2) there are two things that seem to get the persistent herbicides to go away faster, but both are slow and problematic: A) expose more soil to UV radiation via tilling. This will turn your soil into a cement-like dirt. B) Grow grass, which is immune to the effect and takes it up, cut it and haul it away. This, too, depletes your soil of organic matter.

3) the only fast solution I have heard of that has worked, is to remove the top 18 inches of soil and replace it with soil from a weed-infested field.

Another path that some people try is a form of dilution: bring in clean soil and try to cut your half life in half. You will have sickly, stunted plants for a few years. And maybe in ten years things won't be so bad. I would rather have a fresh start.

paul wheaton wrote:I'm tempted to remove this thread because I want these forums to not talk about pesticides or GMOs.

That would be sad. Discussing them is the only way to educate others about their evils and how to avoid their problems and how to recover. Understanding how they work will help towards this goal as well.

Your comments are exactly what I have heard as well. The chemical companies (ie Monsanto) want US to be out of the food prep "business". They will do whatever it takes to accomplish that even poisoning our land and our bodies.

Paul and Judith do make a good point though. The best solution is to avoid those things in the first place. I'm not advocating dumping toxic gick into the compost bin and expecting a golden result. I came across overly optimistic on how well soil organisms and composting deal with this.

I was talking with someone the other day who was very concerned about putting grass clippings in their compost because they used a petrol mower to cut it. This person really wants a garden, but is sending this potential resource to the landfill, and complaining that compost is too expensive to buy in quantity from places like Walmart. This was in the forefront of my mind when I posted these comments, and I'm starting to see this in a few areas of my life where people have so much fear that it's preventing them from any action whatsoever. If this person made compost from their gas mowed grass, and grew their own food in it, the chances are that the toxic gick they ingest as a result will be orders of magnitude less than what they currently ingest from the supermarket.

It's not ideal by any stretch of the imagination, but it's a start in the right direction.

Paul, please keep this thread. Everyone is having a polite discussion, we all have the same agenda, and we're all on the same side. I for one appreciate this, and understand the difference between a passionate position, and someone with an alternative agenda.

As a professional chemist and amateur mycologist, let me expand on Paul's comment. It's true that composting is not going to remove herbicides in the short term. Composting is a bacterial process and bacteria don't see the herbicide as a food source. What will metabolize the herbicide (eat it for lunch) is fungi, specifically a white-rot fungus. The easy way to remember the two main classes of saprophytic fungi is "brown-rot eats the cellulose and leaves the lignin; white-rot eats the lignin and leaves the cellulose". Most herbicides are aromatic molecules, meaning that they look like lignin to any fungal mycelium that is looking for a meal. They will be able to attack it and break it down into smaller components, rendering it "recycled".

Now, how do you do this on your lawn? Here is a reasonable plan of attack: (1) get a truckload of mulch that contains lots of tannins. Oak leaves would be perfect, what you want to avoid is actual structural wood like pine logs or lumber or wood shavings or newspaper, those things are all cellulose. (2) dump the pile where you can water it daily. (3) Go on a mushroom hunt for some white-rot fungi. You can start here with Phanerochaete chrysosporium, which is pretty easy to collect from the underside of a well rotted log. (4) Take your sample of white-rot fungi and whiz it in the blender, say a quarter cup of scrapings in a liter of water. (5) Sprinkle this over the pile of mulch and water it in good. You don't need to bother to cover it, the sun may dry out the top inch or so, but you want to water the pile every evening. Remember that advice when NOT to water your garden because it might cause fungal problems? Now is the time to break that rule -- you want the fungus to take off. After a few weeks, depending on the temperature, you should be able to dig into the pile a few inches and see gobs and gobs of white mycelia. This is good. Now the fungus is ready to do its work detoxifying your lawn. (6) Wait for a day when there is heavy rain forecast and get out before (or during if you don't mind getting wet) and spread your pile of prepared mulch out over your lawn. Not more than an inch thick, you want the heavy rain to beat down on the mulch and drench the fungal mycelia and spores into the soil.

The whole point of this exercise is to really spike the population of white-rot fungus in the top layer of your lawn and start this ecologically dead zone (from all the pesticide and herbicide abuse) back to being a living soil. While the white-rot fungus is breaking down the oak leaves, they will also eat any herbicide and pesticide residues. Dandelion seeds that blow in will now be able to grow. With all that fungal mycelium there, other soil critters will see the "Buffet Open" sign and move in for a free meal. If you mix the grass clippings with this specially prepared fungal mulch, they will also be recycled. But you don't want to do regular bacterial composting; you want slow, ambient temperature fungal growth conditions.

This concludes your mycoremediation class. Student questions are welcome.

John, I could only give you ONE thumb, but you deserve TEN for that very helpful information.

Interesting post, especially John's contribution. Thanks. I have a question though. In the link you gave for the white rot fungus it states that the fungus releases enzymes, hydrogen peroxide for example, which start breaking down the lignin. Would applying hydrogen peroxide directly yourself start the process off?

Ray South wrote:Interesting post, especially John's contribution. Thanks. I have a question though. In the link you gave for the white rot fungus it states that the fungus releases enzymes, hydrogen peroxide for example, which start breaking down the lignin. Would applying hydrogen peroxide directly yourself start the process off?

Maybe in the lab, Ray, but I think it would be hard to implement on a lawn. When you pour hydrogen peroxide on something, it goes and oxidizes the first reducing agent it comes across. If that's a cut on your hand, all that bubbling is the skin bacteria being oxidized by the H2O2. If you were to go and pour some on a lawn, it would oxidize soil bacteria, mineral particles, bleach out the color in any dead biomass, and if there was enough left over, oxidize a pesticide or herbicide molecule here or there. This is where the targeted release of the fungi works wonders. The fungal hyphae grow, absorbing nutrients in the soil as they go along. When they come to a food source, say a shriveled piece of weed that contains herbicide residue, THEN they start releasing enzymes to digest the food. While we in the Animal Kingdom ingest our food before we digest it*, our friends in the Fungal Kingdom do it backwards; they digest their food first and then ingest the nutrients. So the peroxide ends up getting applied where it's needed, when it's needed, in a much more efficient way than we can apply it with spraying equipment.

* Maybe spiders digest their food before they ingest it. Spider venoms contain proteolytic enzymes that turn their ensnared bug into a liquid meal that they can then suck up.

John,

It is true that most herbicides (and most compound toxins) can be broken down by fungi. The catch here is that we are not talking about most herbicides. We are talking about persistent herbicides.

My understanding is that fungi do not break down persistent herbicides such as clopyralid, aminopyralid and picloram.

I would very much like to be wrong about this. If I am wrong about this, this would be a huge gob of awesome sauce. If you have anything that makes it easy for folks to understand, I would greatly appreciate a link so I can share that information far and wide.

Paul, you are right, that persistence was engineered in by chemists. They went a little crazy seeing what they could come up with when they started substituting chlorine for hydrogen on a lot of organic molecules. What they came up with were herbicides like the ones you mentioned, as well as pesticides (like DDT and DDE) that didn't break down quickly. They even got the bright idea to try substituting with bromine as well, giving rise to such environmental horrors as polybrominated biphenyls.

If anything can be called "unnatural" it is the carbon-halogen bond and it doesn't fit into the ecology that has evolved over billions of years. However, once the compound has been de-chlorinated or de-brominated, what remains can be metabolized by all manner of lifeforms. With mankind cranking out tons of organohalogen compounds for all sorts of uses, there are really only two decomposition pathways for this first step: (1) sunlight, which you mentioned in an earlier post, where the UV rays of the sun can break the bond and toss in an oxygen, which then makes it possible to reenter biochemical pathways and (2) cleavage by some oxidative enzyme excreted by a fungus. You already told of the counterproductive aspects of tilling and tilling and tilling, hoping to expose more soil contamination to UV rays. That's really wiping the slate clean before anyone can think of what kind of permaculture they can try to start. So that leaves mycoremediation as the only path forward if you want to decontaminate the soil of chlorinated herbicides and pesticides while at the same time trying to build soil and grow some plants.

Here's a link to a typical paper on this topic: Degradation of Chloro-organic Pollutants by White Rot Fungi, but as far as being easy for folks to understand, that it isn't. Which is why I posted what I did as a possible mycoremediation method to try. There just aren't enough scientists out there studying and promoting mycoremediation and if we wait for them, it might go as slow as tilling the soil over once a year for some fresh sunlight. Permies and other interested stewards of the environment shouldn't be afraid of trying some mycology experiments. You don't have to be a Paul Stamets to try his little trick of directing an E.coli discharge through some mushroom mycelium to try and remediate it, you just have to do your library research and approach the problem with a scientific mindset.

So if people have problems, and no access to a full environmental laboratory, they are going to have to try methods like I outlined and evaluate them on indirect inferences, like how quick the dandelions come back, or how many bugs they see in the lawn, or if they have toads in their yard. When I had a laboratory, I could take samples and analyze them. Now that I am retired, I rely on the indirect methods for my own garden. I can find lots of toads and salamanders in my garden, so I must be doing something right.

cleavage by some oxidative enzyme excreted by a fungus.

I know that fungi will break down a lot of stuff, but I thought this was one they could not break down.

It does seem like it would be pretty easy to do a demo for youtube. I think peas are considered the most sensitive to the persistent herbicides. So it would be good to have three soil samples: control, contaminated and contaminated with fungi. I would think the fungi would need at least a month to clean up shop.

All we need now is somebody that wants to expand their fame by making a youtube video!

If I remember correctly TOMATOES are another viable subject for this sort of test.

So, unless someone has a plot of land that is ALREADY contaminated, you need to find someone that is interested enough to PURPOSELY contaminate the soil with one of those poisons!!!

I've had serious on-the-ground experience with Aminopyralid contamination.

It does NOT get locked up in the humus. It's taken up by the plants - that's the way it was designed by Dow AgroSciences. It's a long-term herbicide that can last for years. Grasses, like corn, hay and your lawn aren't effected directly by the toxins. But they do get into many other plants and cause serious devastation. I lost $1000 worth of plants last spring thanks to cow manure. Papaya, blackberries, multiple raised beds, all kinds of stuff... and lots of trees that still aren't growing right.

This manure had been composted for six months before application - and still destroyed my plants. Turns out, the previous summer - almost a year before I got it - the farmer had sprayed "Grazon" to control pigweed in his field.

In my food forest, there are still areas where leguminous species are growing poorly with distorted leaves. Again... thanks to adding cow manure. Look - I hate to be a total party pooper, but I'd buy 10-10-10 before taking another risk on herbicides.

I've posted on them multiple times and written a couple of articles:

http://www.floridasurvivalgardening.com/2013/03/mother-earth-news-on-aminopyralid.html
http://www.floridasurvivalgardening.com/2012/09/august-natural-awakenings-article.html

I just posted on this same issue next door in another forum:

"I've used Alpaca manure and it works great. One thing to watch: has that llama eaten anything other than un-sprayed pasture? Long-term herbicides have screwed up a lot of gardens. Toxins get sprayed on hay, which is fed to the animals... then the herbicides pass through into the manure and can remain active for YEARS. I had almost my whole garden wiped out last year by contaminated cow manure. If they're buying in feed, it's almost impossible to know if that stuff was sprayed or not - and composting doesn't break it down."

To add to what Paul and John said about remediation, I had luck restoring some of my beds by adding lots of crunched up charcoal and ashes.

I'm not a sissy or a worry-wart... I use humanure compost, bury meat in the yard, etc. All the potential dangers of those things are basically wiped out through normal organic processes. These man-made toxins? Nope. A plant can't take up e. coli through its stem... but it can sure take up these herbicides.

If you don't want to eat pesticide-sprayed grass... and don't want to be end up potentially weeping over plants that have twisted like satanic fractals and will never produce again... don't use it in your compost!

All that said... I'd give your yard a few years to recover, then go ahead with composting. Getting soil life going will be key. Like previously written, fungi are awesome. Even these disgusting poisons will eventually dissipate.

I'd just hate to see you go through the pain and violation we went through. I'll jump off my soapbox now.

David Goodman wrote:I've had serious on-the-ground experience with Aminopyralid contamination.

It does NOT get locked up in the humus. It's taken up by the plants - that's the way it was designed by Dow AgroSciences. It's a long-term herbicide that can last for years. Grasses, like corn, hay and your lawn aren't effected directly by the toxins. But they do get into many other plants and cause serious devastation. I lost $1000 worth of plants last spring thanks to cow manure. Papaya, blackberries, multiple raised beds, all kinds of stuff... and lots of trees that still aren't growing right.

This manure had been composted for six months before application - and still destroyed my plants. Turns out, the previous summer - almost a year before I got it - the farmer had sprayed "Grazon" to control pigweed in his field.

Infuriating story, David. But six months of composting, especially if it was the high temperature anaerobic bacterial type, isn't going to break down the aminopyralid, as you unfortunately found out. I'm going to come back to my sales pitch, that it has to be a process with fungal inoculation and incubation and I will reference it to this paper which has a table on p.2 of all the chemicals that have been shown to be degraded by the white-rot fungus Phanerochaete Chrysosporium, and that was only studies up to the year 2000. As time goes on, more and more evidence is being accumulated about the restorative effects of fungi, but it isn't making it out of the lab and into general practice.

I would venture to guess make the hypothesis that David's addition of lots of charcoal provided more substrate for fungi in general and that was the main principle acting behind the restoration. That's why I have taken to adding biochar to the media that I want to inoculate with beneficial fungi. Biochar means more surface area for fungi to colonize, which means more strands of hyphae secreting enzymes that can break down these recalcitrant compounds.

Just because fungal spores are ubiquitous in nature doesn't mean that enough of the right ones will be in the right place to do what we want them to. If you want lots of enzymatic breakdown by fungal peroxidases, you are going to have to go collect the right species, inoculate it on suitable media, cultivate it to its exponential growth phase, and then overwhelm your pesticide/herbicide/pollutant problem with lots and lots of active mycelia.

P.S. Paul, my peas are done for the year, so I'll have to wait for next winter to try that one in my garden. But tomatoes....hmmm.....maybe I can try that experiment this summer.

"But six months of composting, especially if it was the high temperature anaerobic bacterial type, isn't going to break down the aminopyralid"

Yes sir!

At the point I'd gotten the manure, I had no idea it was contaminated. I didn't even know Aminopyralids existed. I just knew that it had been sitting in a nice big pile aging by itself. I've come across very few problems that couldn't be solved by composting... this one blew my mind.

You're darn right on the fungi. That's where I'd turn now, particularly after becoming acquainted with the work of Paul Stamets. The more I read about mushrooms and their kin, the more fascinated I become with their ability to fix mistakes we'd find impossible to resolve. You might be right on the charcoal. I was thinking like a chemist rather than a mycologist. You just drank strychnine? Chase it with activated charcoal, stat! The filtration effects were what I was looking for. Having read on biochar, I was also familiar with the potential long-term benefits, though since I hadn't inoculated the char with anything before stirring it through my beds like a madman, I wasn't sure if the microscopic soil life would be colonizing it within a reasonable time frame.

I'm convinced, fungi aside, that the very best way to deal with this stuff... is not to put it or anything anything that may have come in contact with it anywhere near your garden.

Wow, fascinating information above, thanks. But back to the Original Poster's question:

Mike Streaker wrote:How long until it is safe to add our grass clippings to a compost pile? I plan to use the compost in the vegetable garden.

First and foremost, follow Paul's lawn care advice and just leave the clippings on the lawn. Don't transfer them to the compost pile at all! Generally, clippings help the grass, and if they contain herbicide that kills broadleaved plants like vegetables, you won't risk harming your garden with them.

If you want to convert the grass into vegetable beds, that would be a different and more difficult issue, but the original question didn't ask about that.

This article lays it out pretty well.

http://www.motherearthnews.com/organic-gardening/herbicide-damage-zmgz13fmzsto.aspx#axzz2VJ73yfcK

I showed my wife the first page (which is all I was able to view and only once) and she said

WE ARE ALL SCREWED

It beats bein' nailed... atleast we have the option of getting un-screwed...

I've been involved in similar discussions about persistent herbicides in compost. An allotment in the UK had multiple tonnes of manure delivered for a communal heap. It decimated their crops for multiple years thereafter.

One interesting idea that came out of that discussion was a simple test to work out if persistent herbicides are a problem or not.

1) Compost as normal, but keep the suspect plant matter in a separate compost heap. In your case, keep you grass clippings separate from everything else.
2) Let it rot until sufficiently broken down (say 6 months)
3) Plant stuff in pots, using your suspect compost in the pots.
4) If everything dies you probably have contaminated compost -> haul it all off to the dump and be rid of it
5) If everything lives, use it on a small selected area to make doubly sure. If all goes well you probably don't have a persistent herbicide problem.

Mike

That elaborate process will be necessary if one receives a large amount of lawn waste and needs to compost it in heaps. But if it is just grass clippings from a single lawn, then the lawn will be healthiest and not require additional fertilizer if you just leave the clippings in place. easiest solution!

True, but the above is a good diagnosis tool if you are in doubt.

John Elliott wrote:As a professional chemist and amateur mycologist, let me expand on Paul's comment.  It's true that composting is not going to remove herbicides in the short term.  Composting is a bacterial process and bacteria don't see the herbicide as a food source.  What will metabolize the herbicide (eat it for lunch) is fungi, specifically a white-rot fungus.  The easy way to remember the two main classes of saprophytic fungi is "brown-rot eats the cellulose and leaves the lignin; white-rot eats the lignin and leaves the cellulose".  Most herbicides are aromatic molecules, meaning that they look like lignin to any fungal mycelium that is looking for a meal.  They will be able to attack it and break it down into smaller components, rendering it "recycled".

Now, how do you do this on your lawn?  Here is a reasonable plan of attack:  (1) get a truckload of mulch that contains lots of tannins.  Oak leaves would be perfect, what you want to avoid is actual structural wood like pine logs or lumber or wood shavings or newspaper, those things are all cellulose. (2) dump the pile where you can water it daily.  (3) Go on a mushroom hunt for some white-rot fungi.  You can start here with Phanerochaete chrysosporium, which is pretty easy to collect from the underside of a well rotted log.  (4) Take your sample of white-rot fungi and whiz it in the blender, say a quarter cup of scrapings in a liter of water.  (5) Sprinkle this over the pile of mulch and water it in good.  You don't need to bother to cover it, the sun may dry out the top inch or so, but you want to water the pile every evening.  Remember that advice when NOT to water your garden because it might cause fungal problems?  Now is the time to break that rule -- you want the fungus to take off.  After a few weeks, depending on the temperature, you should be able to dig into the pile a few inches and see gobs and gobs of white mycelia.  This is good.  Now the fungus is ready to do its work detoxifying your lawn.  (6) Wait for a day when there is heavy rain forecast and get out before (or during if you don't mind getting wet) and spread your pile of prepared mulch out over your lawn.  Not more than an inch thick, you want the heavy rain to beat down on the mulch and drench the fungal mycelia and spores into the soil.  

The whole point of this exercise is to really spike the population of white-rot fungus in the top layer of your lawn and start this ecologically dead zone (from all the pesticide and herbicide abuse) back to being a living soil.  While the white-rot fungus is breaking down the oak leaves, they will also eat any herbicide and pesticide residues.  Dandelion seeds that blow in will now be able to grow.  With all that fungal mycelium there, other soil critters will see the "Buffet Open" sign and move in for a free meal.  If you mix the grass clippings with this specially prepared fungal mulch, they will also be recycled.  But you don't want to do regular bacterial composting; you want slow, ambient temperature fungal growth conditions.

This concludes your mycoremediation class. Student questions are welcome.  

I think this topic of of [soil] bioremediation to safely utilize potentially herbicide-contaminated grass clippings is a "really big deal" and might merit further detailed discussion of practical research methods/experimentation ... we should remember that for many or most folks, the alternative to the likely safe food from the garden [if the plants survived, grew and somehow produced something without chemotherapy] is known UNSAFE food from the supermarket.  

There ARE reports in the scientific literature of it being done successfully with white rot fungi.  When it comes to breaking down pesticides, the most studied white rot fungi is indeed P. chrysosporium/ (as John Elliott mentions) which has shown ability to degrade a wide range of herbicides under different conditions ... when it comes to breaking things down large doses of UV radiation are going to be helpful, as are other stressors like large temperature swings ... but the "canary in the coal mine" will be the living things, eg. weeds, reptiles, amphibians, insects.

I want to compost my grass clippings. Although I have never treated my grass, how can I know if the previous owner treated the grass? I bought my house 4 years ago.  Presently, my yard has plenty of dandelions and other various weed. Previous posts mentioned that if persistent herbicides are present, dandelions would not grow. So can I assume any non-persistent herbicides in my grass/soil (if any) can be broken down with a nice hot compost?

Moe Quinteros wrote:I want to compost my grass clippings. Although I have never treated my grass, how can I know if the previous owner treated the grass? I bought my house 4 years ago.  Presently, my yard has plenty of dandelions and other various weed. Previous posts mentioned that if persistent herbicides are present, dandelions would not grow. So can I assume any non-persistent herbicides in my grass/soil (if any) can be broken down with a nice hot compost?

It is all a matter of probability.  We could go through hundreds of scenarios and assign them all probabilities, but I think the best path is:

your grass is probably safe enough.  Go for it.  

Of course, I think I would prefer a much lazier approach of leaving the clippings there and improving the soil in place.  Or using the clippings for garden mulch.  But, that's your call.