Cat Litter Composting – 08-07-09

Compostable Cat Litter...Composting
Backyard composter dedicated to cat litter composting, moving along quite nicely with the assistance of fungi and numerous other organisms.

It has been ages since I last wrote about cat litter worm composting, and a couple of recent emails from readers (focused on this topic) reminded me of the fact that it’s something I’ve been wanting to revisit for a while.

As some of you may recall, my original experiment involved setting up a Rubbermaid worm bin specifically for the purpose of determining whether or not Red Worms would consume cat poop. Even though I had started using compostable cat litter at the time, I was worried about the potential issues with salts and ammonia (both very bad for worms), so I decided not to add the clumps to the bin.

The initial results were very promising – it quickly became clear that the worms were more than happy to feed on this waste material. After a while, I basically just left the bin to sit without any further additions however (you know me!!). Every so often I would check on it and add some water (it was an open tub system, so it dried out fairly quickly), but that was about it.

Despite the neglect, a sizable population of (small) Red Worms developed, and basically converted everything (leaves, cardboard, cat poop) into worm castings. I’m happy to report that I finally took pity on them a few weeks ago, and dumped the contents of the bin into various outdoor systems where the worms will undoubtedly find a habitat much more to their liking!

So what about all the cat litter waste?

Obviously, I wasn’t about to start sending it to the landfill again – so I needed to come up with some way to deal with it in a more eco-friendly manner. As such, I designated one of my backyard composters as a cat-litter-only compost bin. Since I was adding everything (clumps, poop and all) this time, and since I had a LOT of it (I’d been bagging it up for several months), I figured there was no point even thinking about trying to add composting worms.

My hope was that over time the older materials would eventually mellow out due to decomposition and I might be able to successfully introduce worms at some point. I left the lid off during some rainy periods, and occasionally watered it with a watering can, hoping this would help to flush out some of the excess salts.

Initially the composting seemed to proceed at a very slow rate, with the volume of material in the bin remaining relatively stable. Strangely enough, after my last big addition of cat litter waste (I tend to let it accumulate for awhile before adding it), the level of material in the bin seemed to go down quite quickly all of a sudden. I also noticed a lot of mushrooms growing in the material (as you can see in the image above) just afterwards.

Yesterday, when I was taking some pictures for this blog posting, just for the fun of it I decided to have a peek at the material in the bottom of the bin. I was curious to see how well decomposed it might be. When I pulled up the compost access door I was shocked to see a bunch of fat, vigorous Red Worms wiggling away. Upon closer examination I discovered that the material was not only loaded with worms, but it’s also contains countless cocoons!

Worms Happily Composting Cat Litter Wastes

I’ve been pleasantly surprised many times during my years of vermicomposting, but I have to say that this was one of the best discoveries. I thought for sure that this bin was going to be completely inhospitable for quite some time. Finding such an abundance of huge worms down in the bottom already is a good sign that (compostable) cat litter vermicomposting is definitely a viable option!

I’ve read that worms hatching from cocoons into a new habitat will be able to adapt to that environment far more readily than any worms introduced from another habitat (unless of course that other habitat is very similar). This may help to explain the thriving population of worms. The composter was basically empty this spring when I started using it, but I’m sure there were plenty of cocoons that survived the winter (I’ve had Red Worms in this system before).

Anyway – with the worms doing so well in this system now, I’ll certainly be interested to see how well they keep up with (and tolerate) all the new material I add. I also have another new system (in my head) that I’ve been meaning to make and test out – primarily as a nifty pet waste (vermi-)composter.

I’ll certainly keep everyone posted! I’m also going to add a pet waste vermicomposting section to the ‘Hot Topics’ page.

Previous Cat Litter Composting Posts

Cat Litter Vermicomposting
Cat Litter Composting – Update
Cat Litter Composting – 12-02-08
Cat Litter Composting – 01-05-09

Note: Cat litter composting warrants some caution, and should generally only be attempted by those with previous composting experience. Any dog or cat waste composting system should be separate from your regular composting systems. Cat litter shouldn’t be handled at all by pregnant women or young children.

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    • Jodi
    • August 9, 2009

    Hi – I compost all of my pet waste in a separate worm compost. We have a few 50lb dogs, a cat and a couple of birds. This bin has been in operation for several months and is thriving. I intend to use the castings in my landscaping only. I have a separate worm farm for my kitchen scraps.

    – jodi

    • Kim from Milwaukee
    • August 10, 2009

    Again you’ve pleasantly surprised me, Bentley, with this post. I’ve been ‘outdoor compost bin’ composting my pine/corn/aspen kitty litter thinking the same thing, that it’s not ready for the worms yet, too high of ammonia and too acidic. Now you’ve got me thinking about introducing some worms to see if they enjoy this environment now that it’s cooked down a bit. I’m a little scared, but it looks like it’s working for you, so maybe it’ll work for me, too. Excellent post!!!

    What is it with the mushrooms, by the way? Does that mean the pile is on the acid side? I get them all the time!

    • Bentley
    • August 10, 2009

    Hi Kim – if at all possible, I would recommend introducing a lot of cocoons rather than actual worms (since I’m still not sure how they would handle an environment like this). I would also do all introductions near the bottom of the bin if you can access this zone (via a compost door etc).

    I find that mushroom pop up when there is a lot of carbonaceous mater such as straw, shredded cardboard etc – along with plenty of nitrogen. You may also be right about the pH. I’ve been using a fair amount of peat moss in my litter bin to help keep the odor down, so that (along with the litter) has likely made things a tad acidic.

    • Anna
    • April 24, 2010

    Could you update us on this? Did you winterize this bin and, regardless of whether you did, how did it fare over the winter?

    I’m off to research corn litter now that I know pine may be problematic…

    • Bentley
    • April 25, 2010

    Hi Anna,
    There actually was an update – but I forgot to add it to the HOT TOPICS “Pet Waste Vermicomposting” section. You can check it out here:

    I will also provide another update for that bed very soon.
    Thanks for the nudge!

    • Jim Braley
    • October 8, 2011

    What about composting cat litter with sand mixed in to counteract the clay?

  1. We’ve been composting our cat litter for a while now but instead of using a purchased cat litter product we simply use cheap potting mix. If we could we’d use garden soil but our soil is not a good option. Cats are used to digging holes in the soil to poo anyway as that’s what they do in nature and it means that it’s just the poo to be composted down. It’s cheaper than buying cat litter too. 🙂 Once I have relocated that compost bin I shall introduce some red wrigglers for sure.

    • Toni
    • April 13, 2018

    Hi! So I’ve been putting my kitty poop + clay based litter in the compost and directly into the ground for months now… I’m just now reading about it and apparently it isn’t a good idea! My compost is directly in the ground though, in a fenced pit. Is this ok?? I’m planning on gardening edible things..


    • Bentley
    • April 17, 2018

    Toni – definitely not the best plan with the clay stuff. I tried this one time and ended up with a terrible mess (heaps of clay sludge embedded with preserved ‘cat surprises’ – lol).
    I have now switched permanently over to chick starter feed as my litter and it works very well (and can be composted – but I don’t recommend putting it near edibles)

    • Nonoy
    • August 18, 2018

    If I vermicompost cat poop and litter, then apply the vermicompost to an ornamental like cats whiskers, will vermicomposting the leaves and stems of this ornamental be pathogen risk free?

    • Bentley
    • August 19, 2018

    Hi Nonoy
    Hopefully you are referring to compostable litter (not the clay stuff).
    If I am understanding you correctly, it seems you are asking if vermicompost (made from litter) is given to an ornamental plant, whether or not the plant would end up with lots of pathogens on it.
    Firstly, I would say that you should always be as careful as you can. Wash your hands after working with that type of vermicompost or even those plants.
    That said, the likelihood of there still being pathogens after a long vermicomposting process and then full plant growth cycle is pretty low in my humble opinion – since, even if not destroyed by the worms themselves, competition with other microbes (in conditions more favorable for the other microbes) would lead to a major decline in abundance over time.

  2. Thanks Bentley! Yes, I use either Coco Coir or Tofu litter. I thought about that since I always read that the resulting vermicompost from animal waste isn’t safe to use. Have you ever tried that?

    I’ve been a fan of your site for years. More power to you.

    • Alex Darc
    • October 2, 2019

    Have you had the resulting compost tested for protozoan and bacterial load?
    I mean sure the worms broke the litter down, but did they remove the threat of disease infection?

    • Bentley
    • October 8, 2019

    Hey Alex – no I have not. These are indoor cats so I worry about these things less. I always do cat litter composting in specific systems and the resulting compost doesn’t get used on food crops (usually just sits in the system for many months). Would be interesting to get it tested though since composting worms have been shown to kill pathogens quite effectively.

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