What You Should Know About Composting Cat Litter

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Robert Pavlis

Composting cat litter can help keep it out of your garbage while turning the waste into something beneficial for your garden. Composting litter though is not as simple as composting food scraps and there are special risks you need to understand. However, done right it is easy and safe to compost cat litter.

cat on the toilet holding a paper towel roll
Composting cat litter is a bit harder than just sitting your cat on the toilet, photo source: flamsterette

Cat Poop and Litter

If you have cat poop you can compost it just like any other manure such as dog poop. But cat poop is normally mixed with litter which makes things a bit more complicated.

Is it worth composting? Yes, both to help the environment and to feed your plants. It has an NPK of about 4-10-0.3 (best estimate). That is a good source of nitrogen for your garden.

Most cat owners use a litterbox that is filled with absorbent material that reduces odor. Numerous materials are used including the following.

Soil Science for Gardeners book by Robert Pavlis
  • Sodium bentonite (clay)
  • Amorphous silica gel (crystal litter)
  • Corn
  • Paper
  • Pine or sawdust shavings
  • Tofu
  • Walnut shells
  • Wheat

The most common material is clay with organic material and silica gel being a distant second and third.

Is Kitty Litter Compostable?

Organic material that is made from plants can be composted. However, neither clay or silica gel will compost because they are made from stable minerals. Remember that your soil has clay in it. If clay composted, your soil would not have any clay.

Neither sodium bentonite clay or silica gel are great things to add to soil, although a small amount won’t harm it. For that reason they should not be added to a compost pile.

Cat litter made from organic material can be composted. You can also compost feces that are separated from clay or silica gel. The use of the term “cat litter” in the rest of this post assumes it is of a compostable type.

The Benefits of Composting Cat Poop

The EPA has identified several benefits for composting cat poop.

  • Composting removes raw cat waste from the environment where it can pollute groundwater and streams.
  • Good composting destroys pathogens and produces a safe soil amendment.
  • On-site composting eliminates transporting cat waste to a disposal facility. This saves time, money, energy, and landfill space.
  • Composting produces a quality soil additive that improves both the physical condition and fertility of the soil.

Don’t use Biodegradable Bags

It is common for people to scoop cat waste out of the litterbox, put it in biodegradable plastic bags, seal it and put it in the trash or recycle bin. The problem is that these bags are not really biodegradable. I’ve discussed this in detail in Is Compostable Plastic Really Compostable?

According to a press release put out by the Federal Trade Commission (FTC) in 2015, manufacturers and marketers of pet waste bags were told that “their ‘biodegradable,’ ‘compostable,’ and other environmental claims may be deceptive.

Disposing of Cat Litter

There are a couple of disposal options; trash bin, green bin, toilet, vermicomposting, pet septic tank and home composting.

Trash Bin

This will end up in landfill and may be the worst option from an environmental point of view. Material in landfill decomposes anaerobically (devoid of oxygen) and produces methane which leaches into the air. Methane is 28 times worse than CO2 for causing global warming.

Green Bin

This is only an option in some municipalities. Where it is collected, a proper high temperature composting process will convert the waste into useable compost. This compost is disease and pest free. If you have such a service, this is a good option, except that you loose the value of the compost and it adds extra transport costs to the environment.

Flushing Down the Toilet

Cat litter should never be flushed down the toilet, even if the product is sold as being flushable. It might still clog your drain.

Vermicomposting

The worms will do a good job digesting the poo, but there can be issues with too much urine. Worms are extremely sensitive to the ammonia and salts from urine so you might need to age the material for a while before feeding the worms. You also need to make sure the litter material won’t harm the worms.

Bokashi Composting

Bokashi composting is a special technique that doesn’t actually “compost” (decompose) the ingredients. Instead, it removes oxygen inside the bin, fermenting the materials and killing parasites and pathogens in the process. The finished “ferment” can then put into a composting bin or directly into garden soil for composting.

Pet Septic Tank

There are several commercial products that can also be used. One such device is the Doggie Dooley 3000, (affiliate link) and you can find similar DIY solutions on the internet. You certainly don’t have to buy it.

It’s a pet septic tank disposal system; essentially a hole in the ground where you mix the poo with some poo digester to speed up the decomposition process. Over time the nutrients and organic matter seep into the soil. It does not give you compost for the garden, but at least you’re not sending it to the city for processing. The pathogens are not an issue since you don’t stick your hand into the hole. This system stops working in cold weather, similar to any composting system.

Parasites and Diseases in Cat Poop

The main concern about cat poop are the parasites and diseases which are collectively called zoonotic organisms. Cat feces are especially dangerous for pregnant women and children. They can carry either a protozoa called Toxiplasma gondii or a roundworm called Tocara catiboth of which can cause brain injury or eye diseases.

T. gondii completes its life cycle in cats who can then shed more than 10 million oocysts per day. The shed oocysts are not immediately infectious and must mature by sporulating (a process that takes several days to weeks) to become the infectious form. The cysts are inactivated within minutes at temperatures of 151 F (66 C) or higher which can be attained in hot compost. A feline vaccine for T. gondii is not yet available.

How prevalent are zoonotic infections? A Canada-wide study found that 32% of cats were infected by at least one organism. It is not clear how that translates into human infection, because of a low number of infection events and poor tracking of infections.

Your own pet is much less of a concern since you come in close direct contact with it anyway. You can easily catch zoonotic diseases from their fur, from foot prints on the carpet and from playing with your pet. The danger of zoonotic diseases is also why most pet owners get their cats treated, so they aren’t carriers. In that case composted poop is even less of a concern.

Home Composting Cat Litter

There are some myths floating around about this. Some say it can’t be composted. Others say that there are no useful nutrients in cat waste. Both of these statements are wrong. Cat litter composts as easily as any other manure and with an NPK of 4-10-0.3 it definitely adds nutrients.

Cat poop has a low C:N ratio, about 8:1, meaning that it is a “green” material and needs to be added to browns for faster composting. The litter all has a high C:N ratio and is considered to be a brown. Depending on the litter material, and the amount of urine and poop in the mixture, you might have a perfect composting mixture with a C:N ratio of 30.

Several different composting systems can be used.

Hot Composting Pile

Cat litter that is composted at a high temperature is safe to use. The high temperature will kill the worms, worm eggs, and diseases. How hot is hot enough? The United States Department of Agriculture recommends 145 F (60 C) while industry standards say 130 F (55 C) for a minimum of three days for safe compost.

A home compost pile can reach these temperatures if the pile is big enough, has the right ratio of carbon to nitrogen and is being done in a warm environment (summer time). But home compost piles rarely meet all of these requirements. Unless you are measuring the temperature of your pile, assume yours does not get hot enough which means your compost might contain pathogens.

In that case you have two options. Either use the compost anyway or don’t put cat litter into the compost pile.

If you use the compost, keep it away from the vegetable garden. Use it on the lawn or better still, ornamental beds. That will reduce the risk of any pathogens even more. Consider spreading it around shrubs – an area where you rarely dig, so you are very unlikely to come into contact with the compost.

One thing to understand about pathogens is that they only live for a period of time outside of the animal. Over time the risk of getting sick from compost drops. The longer it sits in the garden, the safer it becomes.

Tumblers and Rotating Drums

These come in a variety of designs that can be either purchased or made at home as described in Composting Science for Gardeners.

These systems compost slower and at a lower temperature, so they won’t kill parasites and pathogens as easily.

Plastic Garden Composter

These are simple devices that sit on the ground. You place compostable material in the top and wait for it to compost. As with tumblers, these systems compost slower and at a lower temperature, so they won’t kill parasites and pathogens as easily.

plastic dome in a garden setting, with a lid to allow you to add compost
Plastic bin composter, source: Snowmanradio

What About Dog Poop?

Dog poop is discussed in a separate post, Can You Compost Dog Poop?

Should You Compost Your Pet Waste?

If you are not concerned about handling your pets and having them roam around the house, I see no reason why you should be concerned about using their composted poop. You are much more likely to catch something directly from your pet.

The large number of pets in North America is starting to make pet poop a big environmental problem. It really is best if you keep your pet waste in your yard and out of landfill. Although health authorities warn that there is a chance of catching a disease from pet waste, the chances are small if you are keep the pet healthy. Given the fact that simply touching your pet can also give you the same diseases, I see little reason not to compost the waste.

FAQ

Q1. Why can’t cat litter be composted?

It can be composted easily if the litter material is made from organic material. If the litter is made from clay or silica gel, the litter material won’t compost. You could remove the poop and compost that.

Q2. Does cat poop decompose into soil?

It does not become soil, but it does turn into organic matter that is then incorporated into soil.

Q3. How long does cat litter take to compost?

That depends on the method used. Hot composting takes about a month. Slower methods can take several months.

Q4. Is cat litter good for the garden?

It’s excellent for the garden providing it with nutrients and organic matter that feeds soil microbes.

Q5. Can you compost kitty litter with food scraps?

Yes. There is no reason why kitty litter can’t be added to all of your other compostable material.

 

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

6 thoughts on “What You Should Know About Composting Cat Litter”

  1. Some people are using wood pellets for cat litter. This is usually sold as horse bedding (add water and it becomes a soft sawdust)or for pellet stoves. It is economical (about $8.99 per 40lb bag) and as compostable as any wood sawdust. Personally I scoop the poop and flush that, then sift the peed-on litter out using a soil sifter. The pellets can be re-used until they are contaminated by pet waste. I have added the peed on sawdust to my garden compost pile. It seems to stop smelling like cat pee within 24 hrs or so, due I guess to natural garden bacteria ?

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  2. We have been disposing of our cat’s litter in our back woods. We use either corn or walnut litter. Withing a couple of weeks we can’t even see where we dumped it. I spread it thinly and in different spots each time. This system works even during the winter where snow pushes everything deeper into the understory.

    Reply
  3. Not a good idea if you have feral cats in your neighborhood or your neighbor allows their cats to roam free. The smell will attract them (their sense of smell is much better than ours) and your garden will become the Neighbour cat’s bathroom. If you live in a more rural area, it could also attract Coyotes and other wild animals looking for prey. I don’t use clay-based cat litter for my cat. I use a natural product called Cederific made from Cedar trees which grow in abundance in my neck of the woods where this product happens to be made.

    Reply
  4. Thank you for opening this discussion…as an ex-veterinary technician who committed 17 years ago to retaining any organic waste I generate on the property, I congratulate you for “nailing it.”

    Reply

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