View up the side yard, looking toward the back yard. The new bin is all pretty and shiny.

Mrs. Homegrown here:

I posted about cat litter composting a while back, and got lots of interesting comments and suggestions. If you’re researching the topic, I suggest you check out that post, the comments especially.

Since then, Erik and I have decided on the method we’re going to try. We’re just going to do straight up, classic composting, Humanure Handbook style. The only difference between this style and ordinary composting is that we’ll let this compost rest for two years before we spread it, to be sure the bad beasties die off. And in case they aren’t gone, we won’t spread the finished compost around edible plants.

No, this is not orthodox practice. It is not considered “safe” to compost pet waste–all the standard advice tells you not to– but we’re doing it anyway, because we trust time and bacteria and worms and our own composting skills to make good compost out of cat litter. Also, the standard advice is mostly in reference to a home’s one-and-only compost pile. You would not want to add cat or dog poop to your regular compost pile. It needs to be kept in a separate pile that is managed more carefully.

The biggest challenge in this scheme for us was figuring out where to put yet another compost container. Our yard is already overrun with barrels and bins. Worse, when we thought it through, we realized we needed room for not just one compost bin, but at least two, maybe three, because of the aging issue.You know, fill one up, set it aside, start on another. The barrels pile up!

The solution is our south-facing side yard. That “yard” is a 3 foot wide strip of sun-baked soil that no one ever sees. It’s divided from our neighbor’s side yard (also rarely used) by a hedge of tenacious jade plants. There is no access to the back yard from the side yard. It has been a wasteland for all the time we’ve been here. This year Erik put in two tiny raised planters there to see if he could grow hops on the side of the house. But it is still mostly unused, invisible space–perfect for compost bins.

The only problem was access. It’s an awkward hike around the front house to get to that side yard. It would be no fun to have haul the dirty litter over there. This is where Erik’s genius came to play. He decided to cut a hole in our back yard fence–a little section of fence convenient to our back porch– and make a small door that will let us dump the litter directly into the barrel, which sits on the opposite side of the fence. We’re already calling this the Cat Poop Portal ™.

The Portal from the back yard, looking down on the drum

 The specs:

• We’re composting in a food grade plastic 55 gallon drum, which we found on Craigslist. It once held brown rice syrup. I prefer to use food grade plastics for compost, especially since we’re dealing with used barrels. Better food residue than chemical residue. 

• Our drum is white because white was all that was available. I’ve heard white degrades more quickly than the blue or black. Don’t know if that is true, but I have also heard that the lifespan of the drum can be extended by painting or covering it with a tarp. We may do one of those things.

• Erik sawed off the top of the drum, because it wasn’t the type with a screw off lid. Rather it had a bung hole configuration. (I’m still trying to become blase about tossing around the term bung hole.) This means we don’t have a lid. We’ll just put a piece of cardboard or wood on top, because we’re classy like that. 

• We drilled lots of 1/2″ air holes in the drum, on the sides and bottom, for air flow.

• We put a thick layer of straw at the bottom, before we added the first deposit of litter, to provide a little ventilation from the bottom. The barrel is sitting on soil, to allow worms and bugs access.

• Once the straw was down, we added our accumulated litter. (Yep, that’s right, I’ve been saving my cat box cleanings just this occasion. Waste not want not!) See my thoughts below regarding types of cat litter. Then we wet down the litter really well, and covered it with a topping of clean straw, and topped the drum with a piece of wood. Let the decomposition begin!

• Note:  Never place a place a poop-filled compost bin near vegetable beds, due to the possibility of bad bacteria leaching through the soil. Ours is remote from anything edible.

The holes inside the 55 gallon drum

Thoughts on the composting:

As I said at the beginning, this is pretty much straight up, normal composting, with the exception of a long aging period at the end. The Humanure Handbook is a good general guide to composting principles as well having special instructions regarding the safe handling of poop. If you don’t know how to compost, I’d start there. That book is widely available, and they have a free pdf on their website. See our resources tab. 


Our cat litter is compostable–we’ve been using both Feline Pine and Yesterdays News–pine and paper, respectively. Compostable litter is made up of a true carbon source–that means plant-based material: corn, wheat, paper and sawdust are all okay. Clay litter, or anything with chemicals in it, would not be appropriate for this. Clay is not toxic, it’s just that it wouldn’t ever break down into proper compost. I don’t know what the clumping kind is made of, so I avoid it–but if your clumping kind is made of unadulterated carbon material, by all means compost it. Litter with baking soda added isn’t a good idea, because it’s salty. Soil does not love salt. I also avoid anything with added scent, because the chemicals used in fragrances are not something I want transferred to my soil.

We’ll soon find out what the carbon to nitrogen ratio is in the typical cat box. The litter is a heavy carbon source. We’ll see how it is balanced by the cat waste (nitrogen), but I suspect we’re going to have to add green stuff, like kitchen scraps, to get it to heat up and decompose. Here’s how we’ll know: if there’s too much carbon (litter), the pile will just sit there, cold and unchanging.

Another thing I predict is going to be problematic about this new cat bin is that we’ll be adding too little material, too slowly. This means it’s going to be very, very slow pile. Mass creates heat. The best piles are big piles. This might have to be addressed by bulking up the pile with material from another source.

My final concern is odor. This is within whiffing distance of both our patio and the neighbor’s window, so we don’t want any cat box miasma drifting around. Initial precautions include covering the surface of the pile with straw, and covering the top of the bin with a board. We’ll see how it goes.

Stay tuned for updates…