Most of my time is spent figuring out what can be composted or how to make things so that they are ultimately compostable, but knowing what not to compost is important too in order to keep your pile uncontaminated and in good working order. Generally, items that were previously living can be composted, but, it isn’t always so cut and dry. If you consider compost as part of your food chain, you’ll want to keep out the pathogens, weeds, toxins, and non-biodegradable materials. Below are 11 things to keep out of the home pile.
Human and pet waste – Waste from humans and meat eating pets (specifically dogs and cats) can contain harmful pathogens which may survive the composting process. Keep cat waste out of your compost pile because of the possibility of infection with toxoplasmosis, a parasite dangerous to pregnant women and their fetus and immunocompromised people. A better option for pet waste is a digester such as the Doggie Dooley, but be sure to install it away from food crops. Manure from herbivores (goats, sheep, llamas, rabbits, etc) is a great addition to your compost pile since it adds a boost of microbes and nitrogen, and is even better when mixed with carbonaceous bedding such as straw. Respect that manure can contain disease-causing organisms, so be sure to wash your hands after building a pile.
Sawdust or wood chips from pressure treated, stained, finished, or painted wood – Older pressure treated wood contains arsenic and other toxins you definitely don’t want in your compost. Pressure treated wood that appears green almost certainly has arsenic. Wood finishes, paints and stains contain synthetic chemicals that have no business in your compost. Sawdust is helpful when you need to add carbon to your pile, but check the source to make sure it came from untreated and unfinished wood.
Meat, dairy and fatty foods (maybe) – It isn’t that meat and dairy won’t break down, but when they do there may be an odor resulting in more wildlife around your pile than you’d like. The fatty foods are slow to break down and they may interfere with pile aeration. If you have the option, send these food items to a commercial or municipal composting facility. If you have a large hot pile, you could try to bury small amounts of meat and dairy in the middle of the heap, but this is a lot of work if you are composting this type of waste on a regular basis. Another at home option is an underground food digester such as the Green Cone.
Coated and most colored and printed paper – Coated paper including coated paper plates have a thin film of plastic which will not break down in the compost. Colored papers such as wrapping paper can contain heavy metals, among other substances not suitable for the compost. Paper is better off in the recycling stream.
Fabrics and clothes – There are a few exceptions, like the hand-made sweater you made with wool from your very own sheep, but for the most part fabrics and clothes are not compostable. Most contain synthetic fibers, most notably the polyester thread that is used for sewing. Finishes (e.g., anti-wrinkle treatment), decals, and some notions and dyes preclude most of what is in your closet from the compost.
Antimicrobials and pesticides (maybe) – Some pesticides can harm your good microbe friends who are doing your composting work. If you don’t know what pesticide was applied or its mechanism of action, it is best to leave out yard waste that has been treated with pesticide. Antimicrobials in wipes and soaps can do the same thing to hard-working microbes. While some wipes might be biodegradable, don’t include the ones impregnated with antimicrobials in your compost. An antimicrobial wipe or two isn’t likely to be the end of your pile, but your compost is all about microbes, so don’t insult them.
Diseased plants – Plants infested with soil-borne diseases should not be composted. Even if you are hot composting, some part of the pile likely won’t be hot enough to kill the pathogen so you may end up spreading the disease through your compost. One option is to burn the diseased plants and add the ashes to the compost.
Weeds – Weeds might make up most of your organic waste at certain times of the year, so there will be great temptation to put them in the pile. Some can be composted without resulting in weedy compost, but try to avoid weeds that have gone to seed. Hot composting will kill some weed seeds, but again, not all parts of the pile will necessarily get hot enough to kill all the weed seeds. Burning or burial is a better option. Also avoid plants that can multiply from pieces of roots, stems or rhizomes. If in doubt, leave them out on a rock in the hot sun for a few days until they are completely dead.
Cigarette butts – You wouldn’t know it from intersections with long lights, but cigarette butts are not compostable. There are many toxins in cigarettes, even the butts. They aren’t worthy of the compost heap.
Biodegradable credit cards and gift cards – Some of the plastic in your wallet might claim to be biodegradable or state it is made from PLA (polylactic acid), a biodegradable plastic. Don’t throw them into your compost, though, as the magnetic strip on these cards is not biodegradable.
Degradable plastic – Degradable does not mean biodegradable or compostable. The latter two require the presence of microbes where as degradable just means that the plastic changes form as a result of an environmental exposure such as UV light. The end result is likely just plastic in some other form rather than the biomass you are after.
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