Cat Poop Compost Installment #2

Drum full o’ cat litter

WARNING: Human waste and cat waste contain dangerous bacteria.  I fully believe that composting is a safe and sane solution to a waste stream problem–that’s why I’m writing about it, after all– I also know that it can be handled badly. (The stories we hear!) So please, read up on the subject before starting. You should have a solid foundation in regular compost to begin with, because all the basics apply. Take a good composting class or find a compost mentor. Read the Humanure Handbook. For complete safety, all cat/human waste compost should be allowed to sit for two years, and it should not be applied to food crops (but it can go around fruit trees).


Last year at the end of July I posted about our experimental cat litter composting solution in The Cat Poop Portal post. It’s been a while since we reported in, and I’ve received some gentle pokes from readers, so this is an update.

Long story short, it’s going slowly. At the time of the last post we’d installed a 50 gallon drum in our side yard. That drum filled up fast. We have two indoor cats now (I think we only had one when this started) and they are slinky little poo machines. Also, we were using pine pellets which require a complete change-out more often than clumping litters, so we managed to fill the drum in about four months. That was faster than I expected, and a little disappointing, but there are two ways to ease this problem.

1) Changing litter, so we use less. Most clumping litters are either clay-based, which is not good for compost, or have sketchy chemicals in them. We’ve recently found World’s Best Cat Litter, which is a clumping litter made of corn. I called World’s Best to make sure there was nothing added to the corn, and they promised me that there’s nothing added to the standard formula–the magic is all in the way the corn is processed. So yes, we’re supporting Big Corn…but what are you going to do? The stuff works really well and is compostable. Now that we’re using it we’ll reduce our overall litter waste volume.  (Of note: our friend John, a madman with six cats, swears by Swheat Scoop, which is wheat based. I don’t find it works for me, but he blames my litter management skills. It’s an alternative.)

2) We’re offloading half-finished cat compost to My Big Fat Worm Bin. Regular readers (and Vermicomposting workshop participants) might remember that composting expert Nancy Klehm had us add a good amount of mature cat litter compost to the mix when we built up the bedding material for the worms. She said she wouldn’t want to foist raw cat litter on the worms, but when it was well broken down they could handle it.

The drum has been, shall we say, resting productively over the winter. Today I went and dug it up to see how it was doing. As with any pile, the stuff on top was less finished–it looked pretty much like a cat box. It isn’t stinky, though, as long as I make sure all the cat poo is buried.

Down lower the material was more broken down. It’s an interesting rusty orange color. But I didn’t get the sense of lots of activity going on. It was a cool pile, and it showed very little insect life. This is not necessarily a bad thing. The pile is decomposing, just on a long timeline. But at this rate of decomposition I suspected it would need at least another year of sitting to be fully broken down, and then it would need to rest even longer for safety. Compost made from carnivore and omnivore poop needs a two year cycle to allow the pathogens to die off.

Digging down all I see is decomposing red sawdust

Wanting to move it along faster, I did what I’d do for any compost pile that was a little pokey: I turned it, and added nitrogen and water.* Shoveling 50 gallons of kitty litter is exactly what I want to be doing on any given Saturday! As I shoveled, I decided that if I didn’t already have Mad Kitty Disease, I’d have it by the end of the day. As if to confirm this, Trout sat in the bedroom window over the poo-bin, wearing a peculiar, self-satisfied expression while he watched me slave away over his waste. (Phoebe didn’t join in, because she doesn’t admit to creating waste at all.)

Okay, he doesn’t look smug here because he’s wondering what I’m doing with the camera. Prior to this I assure you he he looked very smug.

But back to business. For those of you who are new to composting, turning a pile stirs everything up, increasing bacterial activity, making the materials hotter. This speeds decomposition. There’s much debate over whether to turn or not to turn and how often to turn, and I’m not going into any of that right now, except to say that humanure piles are not usually turned, and I’d hoped not to do so with this catmanure pile, either, but necessity drives.

Just like turning, adding a nitrogen source to the pile heats it up. All compost piles are a balance between carbon and nitrogen sources, aka “greens and browns.” Too much carbon and your pile is cool and slow. Too much nitrogen and its slimy and stinky. But if you get the balance right, you end up with lovely compost.

In kitty litter composting, the litter is the carbon and the urine and poo deliver the nitrogen. Starting out on this path, I had no idea how the natural carbon to nitrogen ratio in a cat box would play out. Now it seems to me that the ratio is carbon heavy. Cat litter materials, such as compressed sawdust, are really dense carbon sources and need tons of nitrogen to balance them.

So my preliminary finding on this point is that it might be help to add extra nitrogen when you add a new layer of litter. Extra nitrogen could come in the form of green yard trimmings, veg scraps, urine, fresh horse manure, etc. Today, though, I decided to add alfalfa meal because we had some wasting away in the garage. Alfalfa meal is ground up alfalfa. It’s used as a natural fertilizer and top dressing, and is high in nitrogen. Generally speaking, I think nitrogen should be free, but if you don’t have a lot of scraps/trimmings/spare urine around, you could do worse than to have some alfalfa meal on hand to perk up your compost pile if it’s gone carbon heavy.

Mixing in the alfalfa meal and water

When it was all done, I thought my pile looked a little more loved, and I think it’s going to heat up nicely. I was able to move ten gallons of the more mature compost over to the worm bin, but the barrel is still pretty close to full.

Adding the kitty compost to the worm bin

For the near future we’ll probably be able to send about half our litter to the barrel, and the other half will have to go to the landfill. Eventually we’ll get rid of this big mass of pine litter, and I hope that by using the clumping litter will keep the bin from filling up quite so fast, and will somehow reach cat:compost equilibrium.

*To be clear, I added water because the pile was dryish, not because water in itself is a magic activator to be used in all circumstances. If a pile is too wet, I’d blend in dry stuff while turning. The goal is for the materials in the pile to be about as wet as a wrung out sponge.

Leave a comment


  1. That corncob-based litter caught my eye for a humanure bucket too. Given your comments, maybe I should just pee in the litterbox along with the cat!

  2. I just got a bunny and am going litter train it. I bought the corn based litter, and in protest my husband grumbled about gmos and not wanting them on our farmstead. Do you have any worries about gmos from the corn cob litter?

    I’ve read that rabbit poo is ready to put in the garden without composting, and wonder about gmo litter since it wouldn’t affect pollination. He hopes to keep our home farmstead organic even though we make our income as a medium size corn and soybean family farm. I may have to look into the wheat based litter to keep him happy.

    • We had a lovely little bunny that we litter trained. At least, he was mostly litter trained; I’m a little suspicious of people who claim that their rabbits are completely litter trained. I asked my dad once about the bunny litter (Dad’s a microbiologist and research scientist) and I think he said that rabbit poo was fine, it was the urine that was high in ammonia and therefore I should not put fresh bunny litter directly into the garden, but put it on my compost pile for a season instead. I have a friend who raises Angora rabbits and she has the hutches over a worm pit because the worms do fine with the rabbit mess.

      As for the bunny, watch the chewing!!! We let our rabbit hop around the house during the day so he could get some exercise and I ended up putting the legs of my end table into mason jars because he had chosen them for teething. Never mind a cage filled with fun things to chew, he preferred my furniture. Rabbits are great pets, though, and very sweet.

    • It’s interesting about the rabbit poop question. I’d heard the same thing about urine–only the recommendation was to just let it dry for a week or so before using it in the garden. I just asked an expert gardener who has rabbits, and she said that the ammonia evaporates so quickly that she doesn’t wait at all–that it’s just not a problem.

      Ah, gardening. Ask a question and get twenty answers.

    • It does seem that ammonia evaporates quickly. I’m not surprised that Dad gives advice on the side of extreme caution, though. He’s always been like that. He’s spent so much time in labs that he sees microbial and chemical threats everywhere, probably because they really are everywhere, but it made for a certain weirdness growing up. What other dad shows his sick children lab photos of whatever bug is making them ill? No 12-year-old really needs to know what a flu virus looks like close up, but we did. Dad just loves science in an oddly charming way.

    • We kept our last bunny in a hutch as we got him too late to train him. The poop side of his cage as close to our garden area and we’d just shovel it over and mix it in before planting.

      Watch electrical cords around house bunnies, they have a scent bunnies love (sort of like cats and catnip) and will chew through them.

      Male bunnies have a territory but females go wherever they darn well please!

      Missy litter box trained herself after watching the cats but I think it more about marking it as hers. The cats ignored it.

  3. Great update! To be frugal I use chicken feed instead of WBCL. (Other than price I can barely find a difference between the two.) Do you think the added nutrients will be a problem when composting?

  4. We use Sweet Scoop, as our one male cat won’t have any other litter (and he lets us know in a way I’d rather him not). It’s a really good litter. The only thing I don’t like about it is the dust it creates.

  5. @Kirk: “World’s Best” is made of whole kernel corn, not corn cobs. So I’m not sure if we’re talking about the same thing. At any rate, World’s Best is definitely waaaay too expensive to use in a humanure setup. But I do support your idea of peeing in the cat box! The cats, though, may disapprove. 😉

    @Anna: I don’t know what to make of the GMOs factor (and I do assume WBCT is based on GMO corn because most US corn is GMO at this point–at least that is what I believe, knowing that 80% of packaged foods here contain GMOs) GMOs insert a level the unpredictable and the unknown into all our equations–is it safe to compost? dunno. Is it safe to eat? dunno. What are the long term effect on the environment? Does anyone know? Can anybody possibly calculate all the variables and give us a the “right” answer? I doubt it.

    I’m overall just annoyed that I have to think about this problem at all. One should not have to be suspicious of corn.

    But despite all that, I am composting it. I’ve decided I just may as well. The kitty compost won’t go near my food crops.

    But I guess if your husband is committed to a 100% organic garden, composting with materials not 100% organic–ie gmos– just doesn’t work. You could try the wheat litter–though I’m sure it’s not organic, either, and to make things worse, I understand big wheat is going the GMO route too. Pine litter might be the most “organic” since no one sprays pine trees–but they may be the product of deforestation. Nothing is simple!!!!

    Except this–this is pretty simple: Yes, you can put your rabbit poo directly in the garden. It’s not “hot” when fresh like other manures. Use it as a top dressing–don’t dig it in. Actually, if you want, you can dump the whole litter box around the plants as a mulch, provided your litter is something you want on the soil–and it seems these cat litters may not be the thing, but pine shavings would be okay. Cedar shavings, though, would not be so good. Or you could start a worm bin to dispose of the poop. Worms love rabbit poo.

    @Nancy: This is sort of like the gmo corn question above: complex. Hen feed is high in calcium, and generally calcium helps soil. (Unless you live in a very dry place which already has very high calcium soils) So that seems positive. Overall, my gut feeling would be that this isn’t going to harm the soil if the feed is only supplemented with some vitamins. Some feed, though, has medications and who-knows-what in it, so check the label. Above that, the feed is probably gmo based, unless it’s organic, so then that’s just another factor to weigh in.

  6. Well, I am still transferring our cats’ leavings to their own dug hole in the backyard. Pancho always follows, and even though I have the litter hole covered with some heavy things to prevent nosy visits from the neighborhood cats, he always tinkles in one corner. “Pancho was here!” Well, that is part of his morning ritual outside, anyway. Discrete tinklings in a huge array of spots outside.

    We use Exquisicat Corn litter. It clumps, but is no big whoop other than it really absorbs odor well. And, Lucy would probably start voiding in my shoes if I switched out the litter on her yet again. We’ve tried a huge variety of litters in her brief 8 yrs.

    I had one poor result when we used the Swheat Scoop stuff, a long time ago. I wasn’t able to scoop one morning and when I got home it smelled like they were maintaining a really weird-smelling sourdough starter in the corners of the box.

  7. Paul Stamets did some research with using mushrooms to kill e. coli which is the primary bacterial concern for using animal waste in compost. this may help to speed up the process of being able to use the animal manure sooner than two years. It’d be interesting to do some fecal coliform testing of animal manure compost using mycoremediation to kill coliforms. Stamets work really does call for more research on the subjects, but it doesn’t get much. there was recently a discovery that a fungi from south america can actually break down polyurethane. Stamets did a TED talk, if ya’ll haven’t seen it you should!

  8. I use cat country wheat grass based litter for my house bunny – It claims to be organic but who knows..! I haven’t used corn or wheat based litters because I’ve heard bunnies sometimes find it appetizing, no issues with that with the cat country. There’s no odor at all (with bunnies anyway – I hear mixed reviews from cat owners) except when it’s time to dump it in the compost. The ammonia from the bunny urine at the bottom can knock you out! But it does dissipate fairly quickly over the next few days. Makes the best compost EVER (I scoop old hay into the box, which makes for a bunny poo/urine/hay/litter medley), and mycelium seem to really like it also. Only qualm is the price.. I used to be able to buy a 40 lb. bag of it in Santa cruz for $15, it costs me $27 a bag in foo foo West L.A. Priciest compost ingredient ever.

  9. I wish it were as simple to use pine since we already get some for the chickens. But pine or cedar are not recommended for rabbits. Although they use it at the pet store. Hmmm… Maybe we’ll just have to use a tray and dump it. He’s starting to pee in the litter box, but the poo is everywhere. The chickens eat organic feed we grind ourselves and it’s just too expensive to think about putting in the box.

    My husband is into worms though, so maybe he’ll come up with something he can tolerate. The jars around furniture legs is a great tip! Thanks so much!

  10. We’ve been composting cat waste & litter for a couple of years now with partially digested kitchen scraps. Seems to be a marriage made in heaven. We use small animal bedding (pine pellets), which is very inexpensive. We keep scraps in covered empty kitty litter buckets so that they begin to liquify. The only smell in any of this is when we pitch the bucket of slimy food scraps into the compost ditch. We do this on a day when the neighbors are out! Cover it over with older compost and the whole mess smells sweet in a matter of days when temps are > 40F. When that happens, turn it. Repeat. Wait a bit. When the stuff in the ditch begins to look like compost, we give it a go for a month or two in a tumbler. We would not use the resulting compost in a garden with edibles.

  11. Pingback: Pros and Cons of Different Manures for Gardening

  12. Pingback: dog poop composting — yes or no? a topic revisited

  13. I love that somebody else out there is composting their pet’s waste. I recently began an attempt to compost my dog’s poo because I live in a wetland area and feel irresponsible leaving that fecal matter an environment that feeds our local water source. Bagging it up in plastic and sending it to the dump doesn’t make sense either. I am mixing the poo with yard trimmings, paper, etc.. not food because where I live brown bears are a concern.

    If this works, I’d like to add the finished compost to a worm bin (in garage with food scraps) to make it a bit more likely that pathogens will die.

    I’ve never used a worm bin before, though. What is the relationship between your cat compost and your worm bin? Any suggestions for success would be appreciated!

  14. I’d love a third installment in your cat poop composting odyssey. How are things going now that you are a couple years into it?

  15. Great info! I’ve been composting for a while, but I’m really getting to where I just can’t handle throwing away kitty litter. I’ve decided on making a second compost bin, but the place I want to put it is right next to my regular bin (which goes on edible plants). Do you think this is safe? Or should it be in a totally separate area?

  16. I know this is kind of late in the world of comments, but I worked for Blue Buffalo for awhile and they have a kitty litter made of ground walnut shells that clumps. it is also very good on absorbing the odors of the cat box, it has a smell very much like wet tea leaves.

  17. Pingback: Pros and Cons of Different Manures for Gardening | SHTF R U Ready?

  18. The summers here are long, dry, and hot zone 9.5. A solar oven can cook feces at temps over 200F easily. Are cat feces a concentrated enough plant nutrient source to be worth the effort?

Comments are closed.