Sunday, March 8, 2009

What to Compost

Ah, the age-old quandary: What can you put in the compost bin?

Well, for starters, let's throw out the stuff that should never be put in your compost bin. Remember what your compost bin is for. It is a place to dispose of organic matter (things that were once living) where it will decompose rapidly via natural processes to produce a soil amendment that you can then add to your garden or other plantings to increase the health and nutrient content of the soil. So that sentence should give you some pretty good clues as to what you can't put in the compost bin. Here are some basic criteria:

1) Don't put anything in the compost bin that won't decompose. For example, don't put metal, plastic, ceramic, small cars, etc. into the compost because it will still be there when you try to use the compost.

2) Don't put any chemical contaminants in the compost. One problem is that they may disturb the natural processes that you are relying on for decomposition. Things like gasoline, pesticides, herbicides, fungicides, motor oil, wet concrete, etc. are not good for compost. Also remember that if you are trying to garden organically, it means compost and not using pesticides and herbicides and such. So contaminating your compost with that stuff, is kind of shooting yourself in the foot.

3) Don't put any natural contaminants in the compost. There are other, biological contaminants that you also want to avoid putting in your compost. Examples include weeds that have gone to seed and contain seed heads, plants that died of a disease, and plants that were killed by herbicides, and pet waste. Generally waste from carnivorous pets, like cats and dogs, can carry a number of parasites that can also be infectious to people. Waste from herbivorous pets, such as rabbits, is pretty safe and can usually be added to compost.

Okay, so what SHOULD you put in the compost bin? Let's get the obvious out of the way first. Yard debris, lawn clippings, fallen leaves and kitchen scraps are what compost bins were made for. But don't forget that if it has plant origins, it just might be compostable. That includes paper towels, tissues, 100% cotton clothing, cardboard, newspaper, paper plates, and many more things. Just look at what made it. If it is 100% plant-based, there is a good chance it is safe. I personally shy away from glossy printed materials, be they cardboard, paper plates, or newspaper. I have heard that kaolinite, which is a kind of clay, which is a kind of dirt, is used to make things glossy, but I don't know enough about the process to trust that there isn't something else in there I don't want in my compost. I also compost some clothing, but stay away from zippers, iron-on decals, and the like. Every now and then I pull a strip of elastic out of my compost.

That leaves us with the controversial items. I'll list them here along with my opinions on the matter:

1) Wood - I tend to throw it in. It can take years to break down, but eventually it does. Especially if there is good fungus involved and lots of moisture. Smaller pieces break down faster.

2) Meat - One of the cardinal rules of composting is don't put meat in the compost. I have yet to read a compelling reason for this. All they say is "it attracts pests." It has been my experience that COMPOST attracts pests, whether or not there is meat in it. Meat is obviously organic material. Also, two of the most common organic fertilizers are blood meal and bone meal, both of which are by-products of the meat packing industry. So I do actually put meat in my compost, with a few guidelines. I only put small amounts in. I prefer scraps from cooked meat. I steer clear of raw chicken because of salmonella issues. I also avoid bones because they take longer than wood to fully decompose.

3) Dairy - The same reasons are given for not putting dairy in the compost as for meat. I think they apply even less to dairy than meat and compost it freely.

4) Vegetable Oil - Large quantities of this are produced as a by-product of deep frying, and are often difficult to dispose of. The popularity of vehicles run on biofuels have made this process easier, it is still not terribly convenient. So, can you just dump the oil in the compost bin? Well, first of all, it is VEGETABLE oil, so I would say you can. In fact, I have done just that more times than I can mention without any ill effects to my precious compost. The trick is to do it with care. The main factor to be aware of is what percentage of your compost has become pure oil. Too much oil will smother the very life that you are trying to culture. I have always had a large compost bin and have dumped in less than a gallon less than once a month. If you fry a lot and generate huge amounts of fry oil or have a tiny, kitchen compost bin, you might want to find another disposal method for your fry oil.

Just remember, compost is like your own personal recycling operation. It takes items out of the trash stream and converts them into the best soil amendment you can get.


  1. I could not have said it better myself.

  2. Yes, sensible talk. You compost a lot more than I do in the bin. Wood and (most) leaves go elsewhere, and most paper and cardboard gets recycled. But all kitchen scraps go in. Since we don't eat all that much meat, and I bungee the bin shut so critters won't get to it, it's not a problem.

  3. found this randomly, but wanted to comment that the main reason people who are serious about permaculture/etc. don't compost meat and dairy (and manure of meat-eating animals) is because they have been found to contain pathogens, not because of the pest issue. i guess you'd be alright if you didn't use your compost to grow things that you eat, but if you do, you could potentially become sick.

  4. Ben - I agree with you with regards to raw meat and manure of meat-eating animals. However, I disagree completely with regards to cooked meat and dairy products. Those things are meant to be eaten. If you worry about disease, the act of physically putting them in your mouth would be by far the biggest risk. Yet that is what they are meant for. By comparison, putting it into a bin where it will be subject to intense biological processes for months, including likely being consumed once or twice by larger creatures, and then spread on the dirt to maybe come in contact with a plant that will be washed or cooked before consuming is a mighty small risk, comparatively.

  5. Most municipal hazardous waste recycling centers will accept new/used cooking oils. Unfortunately, not all centers remain open throughout the year. Freezing prior to composting sounds like a good alternative. Don't throw it down your sink. The issue is larger than whether you can keep your pipes clear with some dish soap. The oil eventually ends up in the sewer system & costs cities millions each year to unclog.