Cat Litter Composting – 01-05-09

Corn cob cat litter – amazing stuff!

This is yet another blog series that I haven’t been updating as regularly as I had hoped. I’m sure some of you have been wondering how my cat litter vermicomposting experiment has been going. Well, I am happy to report that it is indeed still going. In fact we’re only just getting warmed up here.

I’ve decided to really take my time with the project, not only because of my own time constraints but also for the sake of making sure the system I am using stays relatively balanced (a challenging feat for most new vermicomposting bins). That being said, I have actually upgraded the system to a 55 liter tub (previous was ~ 20 liter container), and have added a lot more material – including a lot more cat poop. I should mention that I’ve decided to not add the urine clumps to this bin given the fact that is a relatively small system with no drainage. Urine contains inorganic salts which can accumulate in the system like this, potentially causing harm to the worms. In a large outdoor system this wouldn’t be nearly as much of an issue (and I’ll definitely be demonstrating this once spring arrives).

While I still haven’t directly added many worms to the system, I have added a lot of spent worm bedding (ie most of the worms were harvested from it) that actually seems to now have a major abundance of smaller worms in it. The worms that were already in the smaller bin seemed to be doing very well (have grown in size etc), so I suspect that I will have a thriving bin in no time.

I will more than likely now leave the new bin to sit for a month or two without adding much of anything to it (other than the occasional sprinkle of water since it is an open system), but will of course provide some updates along the way. Once the worm population is nicely established, I will definitely start adding the cat waste on a more regular basis.

As far as the cat litter itself (PC Green Cat Litter) goes, I really can’t say enough good things about it! Now that I’ve used it for a couple months, I know for a fact that I will never go back to normal litter again. While it may seem like it is a more expensive product, I’m convinced that it actually costs about the same amount, since it lasts longer in the litter box before stinking too much (still have not reached that point) – ie. the point at which you have to dump the entire remainder of the material in the tray.

With my typical litter box cleaning schedule (scooping every couple days or so) the room where the two litter boxes are located never smells excessively of cat litter – and it is a tiny bathroom, so this is no small feat. This was certainly not the case when using the regular litter! Apart from that, the cleaning and tossing aspect of the regular clumping cat litter was vastly more annoying. Not only is it much much heavier stuff, but you have to toss it out with the regular garbage.

All in all, I am so happy that I decided to make the switch!

Previous Cat Litter Composting Posts
Cat Litter Vermicomposting
Cat Litter Composting – Update
Cat Litter Composting – 12-02-08

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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    • Atlantis
    • January 6, 2009

    I recently added used clumping all natural pine kitty litter to my thriving worm bin — no urine clumps or waste. I added water to off set the dryness. All but a handful of my worms died (Had about 8 – 10 pounds). I added some pulled weeds and kitchen scraps to what was already there. Watered it again to be sure it is moist enough (about like a damp sponge) and am letting it sit. Any suggestions on how to get my farm back in order? I didn’t find anything about pine being bad for worms when I researched.

    • Bentley
    • January 8, 2009

    Sorry to hear that, Atlantis. 8-10 lbs?? That’s a terrible loss!
    Since you didn’t add the urine, I suspect you must be right about the pine. I have heard that cedar can harm worms but never a specific mention of the dangers of using pine. Perhaps there is something else in the litter as well?
    Hopefully those survivors will produce a population of super worms for you (obviously pretty tough little guys if the only survivors).

    In a situation like that I would likely mix in a lot of shredded cardboard, fall leaves (if I had them) and mature compost (if I had it) to try and reistablish the balance. I would then simply let it sit for awhile. I wouldn’t recommend adding any new worms to that system until you are 100% sure it is ok. If it looks like the worm population is making a comeback that will be a good sign. Don’t give up though – it is amazing what can happen even when you let a completely dead bin (which yours isn’t) just sit. Worms that are born into a certain environment are much better adapted to that environment than adults introduced into it.

    • Angie Hill
    • January 16, 2009

    I have four cats. They use pelleted pine sawdust cat litter. I have one designated cat-poo wormbin which is a large adapted plant pot. I separate the cat-poo from the litter, and add to the wormbin-The urine-soaked cat-litter gets used under thick cardboard mulch along paths in my garden. This suppresses weeds very well, and also eventually degrades, encouraging beneficial microbes, and of course,worms! I’ve not had any problems with the worm population. In fact, it seems to thrive on the cat-poo! I did one similar years ago with dog-poo. Same results. Great vermicompost after a year or so, which I used in flower beds and the lawn-not on vegetables just in case there were any pathogens lurking. Sad about your worms dying, Atlantis, but I think it might have something to do with the amount of cat litter added to the system. The sawdust will be carbon, which is good, but the pine may still have turpene residues. I would only add that in small quantities. Hope this helps.

    • Angie Hill
    • January 16, 2009

    Meant to add that I (well, the cats!) tried the paper based cat litter in their litter trays with no success-all 4 cats went outside the litter tray!!! 🙁 The only other “green” alternative here is the pine sawdust based one. In the UK we don’t have corn husk cat litter. I’m seriously thinking of trying chipped or shredded hedge prunings soon, so watch this space. If they are willing to use this, then it would mean fewer plastic bags of bought stuff, and of course, fewer trips to the petshop.

    • Jessica
    • August 3, 2009

    Any updates on vermicomposting the cat waste?

    What about the C:N balance? Do you think using newspaper-based litter – e.g. either shredded or straight up newspapers ( or a commercial pellet product ( – might help to maintain such a balance?

    For those who are interested, here is a link to a very interesting student experiment on vermicomposting cat litter:

    I find the idea of rotting cat litter in a landfill to be the worst aspect of cat ownership so I’m particularly interested in the status of your own experiment.

    • Bentley
    • August 7, 2009

    Hi Jessica,
    Sorry for the delay responding – I just posted an update on the cat waste vermicomposting front. Thanks for the nudge.
    Here is the link:

    C:N balance isn’t quite so important with vermicomposting as with regular composting – although, that being said, I don’t mean to imply that it’s OK to have a low C:N (since that may result in the release of ammonia which is not a good thing). What I mean is that it is totally fine to end up with a habitat (including food) that has a high C:N ratio, and in fact, it’s not a bad idea to aim for this. What I’ve been doing apart from relying on the carbon-rich (corn cob based) litter material is adding other carbon-rich stuff like peat most, cardboard, straw etc.

    As I wrote in my update post, everything seems to be working even better than expected!

    You are absolutely right – there is NO reason that cat litter waste should end up in a landfill. Well OK, the nasty stuff you get when you use clay-based litter can only really go to the landfill. BUT – everyone should explore compostable alternatives! I love the stuff I’ve been using – so much nicer than the normal clumping cat litter! Being able to then feed it to a herd of worms is just like icing on the cake!

    • Lia
    • April 22, 2010


    I am in the process of obtaining my very own worm bin (quite ridiculously excited about this, actually) and have been reading conflicting reports on composting pet waste. We have a total of seven cats and use the natural pine litter (vastly superior in odor control and length of usage compared to clay litters that have been used in our household). I’d love to be able to compost this, even if I just turn it into soil to help level out the back yard! I do have a smallish area behind the shed that is shaded where I could fence it off (from the dog) and perhaps work an in-ground bin, as I really don’t want the litter exposed.

    I’ve been reading and researching, but I’m still kind of lost at where to start something like this, especially with conflicting reports on pine litter. I don’t mind terribly that it hits the landfills right now as I figure it will eventually decompose there and help other things decompose there, but I would rather be able to compost it at home if possible.

    If I’m reading right: It looks like if I build a large enough bin (open bottom? size recs?) that I can easily tuck into the corner behind the shed will hold all of the litter (urine soaked/dried and all) and if I mix it with leaves and plant material and just keep it turned periodically, it should mellow out enough to add worms or have the worms show up on their own? I have a front yard of shade that gets a thick coating of dead leaves and pine needles, but again, PINE.

    Help would definitely be appreciated and thanks is already given as I’ve been learning tons and can’t wait to have my first batch of veggie-ready compost from the kitchen waste. 🙂

    • Angie Hill
    • April 28, 2010

    Hi! I wrote about my own experiences with composting used cat
    litter last January. I have just emptied my first cat poop wormery, and it’s not only fullof healthy looking red worms, the vermicompost looks great-and I shall be using it under some new fruit bushes I am planting. (Under meaning in the planting hole, not as a mulch after planting!). I think the trick is to separate the poop from the main bulk of pine sawdust-the sawdust needs weathering/ageing for a while before adding to a worm bin. I still use the sawdust under cardboard, finally adding a layer of shredded leylandii to make great paths between my vegetable beds. It seems to suppress weeds, and eventually decomposes, attracting fungi and loads of worms to finish the job!

    • Chris Picher
    • November 18, 2011

    In Durban S.Africa friends and I kept stables and all the wood chips/sawdust, which we used for bedding, plus the urine/manure went into a heap. This heap turned into magnificent compost. Now it did heat up but it was home to the finger sized grubs of some sort of moth or beetle. The dropings of these grubs were the main component of the compost.

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