What Not To Do With Grass Clippings

or, how Miss Smarty Pants messed up her compost pile in one fell swoop.


There is book knowledge and there is practical knowledge. How I came to mess up my compost pile and pollute my neighborhood with the stench of ammonia is an example of me having the first and lacking the second.

Let’s back up. This past winter and spring, I took University of Rhode Island’s Master Gardener classes. Sixteen weeks of course work and 50 volunteer hours (still working on) to obtain that title. The classes were a joy for a gardening geek like me. A student again with a notebook, listening for hours to people talking about gardening – plants, bugs, soil, weeds, compost – in the company of 100 people with the same obsession. Was there every a happier student? 

Among the classes: a session on composting. Well, this was old hat for me. I’ve maintained a small compost pile for years. Starting yearly with the fall leaves that land on my property and adding fruit and vegetable scraps as they arise, my little (80 gallon) plastic compost  bin served me well for years. But my composting method (dump it in and let it sit, with an occasional stir to keep the odors at bay) is a slow producer, and it takes a lot of leaves and kitchen scraps to make a usable amount of compost. But I was happy to be making compost, as opposed to actually using it. I felt environmentally responsible by not trashing food scraps or sending leaves off to Johnston for use as landfill cover (as they used to do).

But now, I’m (almost) a Master Gardener! I have an obligation to up my game! So I found some pallets, applied my amateur carpentry skills (another obsession) and built me up a legitimate one-third of the three bay composter that real gardeners use. Yeah! I rounded up all the leaves I could find (which in my yard are still on the ground in spring – I’m a lazy raker) – and set them a-composting.

Well, the science of composting – of which I’ve been aware but have given little attention - was that compost is best made with a 25:1 ratio of carbon (e.g., brown leaves) to nitrogen (e.g., kitchen scraps, fresh green stuff). That’s what the bugs that digest the raw stuff need. One can go a bit nutty figuring out how to achieve this balance using leaves (a 35:1 to 85:1 ratio), food scraps (a 15:1 ratio), and vegetables trimmings (a 25:1 ratio, although I’m not clear what the difference is between food scraps and vegetables trimmings). So, not being one to fixate on details, I typically wing it. It’s more a matter of using what I have on hand than concocting a specific blend.  My philosophy: stuff rots; it’ll get there.

The limiting factor has always been getting “stuff.” Making lots of compost requires lots of stuff, and short of pilfering curb-side bags of lawn waste on collection day, I’m limited by what my R-10 plot can provide. But then there’s my neighbor, who, as a Certified American Male, is obsessed with his grass and generates grass cuttings at an amazing rate (judging by the number of lawn bags he fills each week). 

So I ask him about his grass, and he doesn’t use chemicals (except fertilizer), and he’s more than happy to give me his cuttings. I ask him why he doesn’t just leave them on his grass and, while I suspect it’s all about appearances, he cites “thatch control” as his reason. I show him my one-third-of-the­-three-bay-composter-that-real-gardeners-use and ask him to dump his grass clippings in there at his leisure. Two days later, on a Monday, my previously half empty composter is filled to the brim, and a bit beyond, with grass clippings. Lots of stuff!

Well, grass clippings are high in nitrogen (19:1), a good complement to my largely leaf-filled compost pile. However, my grass clipping composting experience is limited, seeing as I always leave the cuttings on the grass when I mow – which is actually the best thing to do although my real reason is the aforementioned laziness. 

So the week goes on and I’m focused on work things with little time to garden. On Friday, I awake to the strong smell of ammonia. I first blame my indoor cats, but after checking (and changing) the litter boxes, I conclude they are innocent. Then I blame the local outdoor cats, who visit my brood through the windows often and mark their presence. But then I notice that the compost pile is steaming. For a fleeting moment I think I have attained the illusive “hot compost pile”, but then realizing I haven’t mixed in the grass clipping yet, conclude that this steaming is probably not a good thing.  

The clippings have turned into slimy, steaming, oxygen-depleted clods of rotting grass, stinking of ammonia. A hot mess, as my daughter would say. The only way to remedy this so my neighbors on the other side don’t complain (who have been silent on the one-third-of-the­-three-bay-composter-that-real-gardeners-use on their property line) is to deconstruct the entire compost pile, get air and more carbon stuff in, and hope that it remedies the problem. This was the bulk of my Memorial Day. Four hours of tearing the pile apart, spreading it on a tarp, hand-ripping each and every nasty slimy grass clod I could find, mixing it with shredded paper (the carbon), and then shoveling it all back into the bin. All while being gassed by ammonia.

I should have stopped this experiment when I asked my neighbor why he didn’t leave the clippings on his lawn to decompose. I should have explained to him that thatch - that intermingled layer of living and dead stems, leaves,  and roots that accumulates between actively-growing grass and the underlying soil – is not caused by grass clippings. Thatch is composed of those parts of the grass plants that are most resistant to decay – stem nodes, crowns, and roots. Although grass clippings may get in the thatch layer, they usually don't contribute to thatch build up because they are mostly water and are easily broken down by soil microorganisms, usually within a week. And they add lots of nitrogen to the soil so less fertilizer is needed.  Leaving them on the lawn is a win-win.

Thatch occurs when plant material builds up faster than microorganisms can break it down (e.g. due to over-fertilization) or when lawn management practices reduce the number of organisms in the soil that decompose thatch (e.g., use of insecticides that reduce earthworm and soil microbe populations). A good thatch primer is here: http://cropsoil.psu.edu/turf/extension/factsheets/thatch.

So for now, I have to downscale my composting ambitions, and must remember to tell my neighbor “thanks but no thanks” to the grass clippings. I hate to see it go to waste, but I just don’t have enough brown stuff to mix with the clippings. At least until fall, and at least until I have two-thirds-of-the­-three-bay-composter-that-real-gardeners use.

If you, like my neighbor, are a Certified American Male obsessed with your lawn and some slightly loopy lady from next door asks for your grass clippings – give them with abandon! But make sure the loopy lady knows what she’s doing (or deliver them on a Friday) so you don’t end up an accomplice in the gassing of your neighborhood. Or better yet, keep the clippings on your lawn.

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.

kelvin May 30, 2012 at 02:19 AM
Probably not how you planned on spending your Memorial Day - minor setback with the composer but your hard work should pay off. URI also offers a six week Master Composters course as well - alot of good info if you have the time. I don't think it's necessary in your case since you have the basic concept - maintain adequate air flow with proper ratios and your microorganisms will do the rest. Also keep in mind your moisture level - your micros like it wet. Looks like we are in for a little rain but if it doesn't come, you may want to add some water. Good Luck


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