So, you’ve decided to start composting, but you’ve heard there’s a ton of stuff you can’t add to a compost pile. There’s no need to be intimidated, you’ve come to the right place.
Cut through the confusion and take a read-through of what you shouldn’t put in your compost heap.
What Is Compost?
Before I tell you what items to never compost, you should know more about composting in general. To jump ahead to the section on what not to compost, click here.
Finished compost is food scraps, coffee grounds, grass clippings, and other organic materials that have been broken down by chemical and physical decomposers—microorganisms, worms, and fungi—in a decomposition process called composting. Organic material is placed in a compost heap, where it’s then digested and turned into a natural fertilizer. It contains multiple nutrients:
- Phosphorous
- Potassium
- Nitrogen
- Manganese
- Sulfur
- Zinc
- Carbon
- Iodine
- Magnezium
- Iron
- Calcium
- Copper
- Boron
Once the decomposition process is finished, the compost resembles dark soil, but the above nutrients make it much more fertile.
Types of Composting
As you might expect, composting is the process of creating compost. It involves adding the right organic waste to your compost pile and aerating it to create a nutrient-rich material.
Microorganisms, fungi, sowbugs, worms, and other critters fuel the decomposition process by digesting the organic matter. Some or all of these organisms will be present in your compost pile, depending on the type of composting you use.
Compost bins come in various types, each of which are used differently and offer their pros and cons. There are six main types of compost bin for you to choose from.
Hot composting
As the name suggests, hot composting uses heat to encourage the composting process. This speeds up the process and kills pathogens such as those in diseased plants—these usually can’t be added to compost, as plant diseases can spread across the compost and affect your garden soil. Hot composting also uses aerobic decomposition, a process that involves aerating your mix to add oxygen. Several types of composting bins apply the principles of hot composting.
Stationary composter
A stationary compost bin is the most common way to break down a compost pile without much effort. Just add the right ratio of materials and mix with a shovel or pitchfork every few days to encourage the aerobic decomposition process.
Composting tumbler
A composting tumbler makes aerating and mixing organic matter easier than other types of compost bins. Tumblers usually contain two or more chambers so that you can work on more than one batch in different stages of decomposition at a time. They also make it easy to aerate, since they spin on an axis and don’t require the use of a pitchfork or shovel. Check out my article on the best compost tumblers for more info.
Food waste digesters
Featuring a lower basket installed under your lawn where the compost pile breaks down and an upper cone you place food scraps and other waste in through, food waste digesters are a perfect composting system if you want to see the benefits of composting for your garden without needing to aerate and harvest the compost.
Cold composting
Also called anaerobic composting, you won’t need to spend time aerating your compost pile with this method. You’ll simply need to set up your composting bin and add your waste as you create it. This method is not as popular as others for several reasons. It takes longer, it’s more likely to emit an odor, and it releases more methane emissions than any other composting method, which defeats the purpose of composting.
Indoor composting
For those in apartments or small homes, indoor composting is just as convenient and easy as composting outside. There are a few different types of composting you can do indoors.
Bokashi composting
Bokashi composting reduces any potential greenhouse gas emissions with fermentation and a low pH. You’ll need to add bokashi inoculant to the mix to encourage fermentation. Since it doesn’t take up much space, it’s a good option for composting in an apartment.
A bokashi composter features a five-pound bucket with a sealed lid and a spigot at the bottom that lets you harvest the compost.
The things you can and cannot compost are slightly different for bokashi, so be sure to read my article on the topic.
Vermicomposting
This method of composting can technically be done indoors or outdoors, but indoors is best to protect the worms. Maybe best known as worm composting, vermicomposting uses aerobic decomposition, making it similar to hot composting. You’ll swap the heat and aeration for red wiggler worms, however.
A worm composting bin doesn’t need much action from you aside from adding your kitchen waste. You can buy a ready-made one online or you can make a worm compost bin yourself.
Countertop food waste processors
If you’re not interested in creating your own compost but want to cut down on your kitchen waste, a countertop food waste processor is a natural choice. These grind up and dehydrate waste and the resulting material can be used the same as standard compost. Read my article on the best countertop food waste processors to begin easily composting indoors.
Composting Benefits
Composting needs a bit of ongoing effort and an initial investment, but the benefit output drastically outweighs your input.
Healthy soil
Soil health has a direct correlation with climate change, desertification, natural disaster, erosion, human food supply, and more. Maintaining and improving soil health minimizes—if not outright prevents—many of these conditions. Compost adds nutrients, moisture, and organic life to the soil, making it denser and improving its pH levels.
Plant growth
One of the benefits to adding compost includes improving your soil’s cation exchange capacity, which provides more nutrients to the crops, plants, and grass growing in it.
A freshly treated lawn will have lusher, greener, grass, and tomato plants and other crops will grow larger and faster with fewer resources.
Flowers take advantage of the life-extending materials included in compost and will bloom faster and longer.
Less watering
Lawns treated with compost retain more water, so you should see your water bills come down without negatively impacting your lawn quality.
Agriculture represents the greatest use of water around the world. Composting reduces the need for water—an acre of soil that sees its organic matter improve by 1% with compost needs 20,000 fewer gallons of water per year.
Fewer greenhouse gasses
Food and yard waste makes its way to landfills when it’s thrown out, where it’s then covered by thousands of tons of trash. Sealed off from any oxygen sources, it breaks down through anaerobic decomposition.
The microorganisms responsible for this process emit biogas. Composed of methane and carbon dioxide, this dangerous gas traps heat in the environment and encourages climate change. Composting your waste reduces this.
Alternative to chemicals
Store-bought pesticides and fertilizers contain toxic chemicals that damage soil and water over time, and even threaten aquatic ecosystems. The Environmental Protection Agency notes that they’re also harmful to human health. These harmful chemicals aren’t found in compost, making it a harmless alternative.
What to Compost
Figuring out what to compost isn’t complicated. As long as you have the right mix of brown and green materials and chop up the materials to make them easier to break down, you can compost the following brown and green materials:
- Untreated garden waste
- Vegetable waste
- Dry grass clippings, lawn trimmings, and other yard waste
- Food scraps and other food waste
- Coffee grounds and coffee filters
- Biodegradable packaging
- Fruit scraps
- Tea bags
- Eggshells
- Wood ash and wood chips
- Paper bags
- Onions and garlic scraps (in moderation)
- Banana peels
- Nutshells
- 100% cotton and wool rags
- Leaves
- Hay and straw
- Pine needles
- Shredded newspaper
- Fireplace ashes
- Houseplants
- Leaves
- Hair and fur
- Cardboard
- Paper and paper towels
- Corn stalks
- Wine corks
- Potted plants
Never Compost These Items
And now, onto the big question—what not to compost. It’s a long list, so get comfortable. You’ll need to avoid the following materials:
- Meat scraps
- Animal fat and other animal by-products (these attract unwanted pests)
- Animal waste/pet waste/dog and cat feces/cat litter
- Toxic plants
- Lawn trimmings recently treated with chemical pesticides
- Diseased plants
- Diapers
- Rice
- Synthetic soaps
- Sawdust
- Cigarette butts
- Synthetic fibers and clothing
- Stickers from fruits and vegetables
- Walnuts
- Fish and other seafood products
- Colored or glossy paper
- Charcoal ash
- Coal ash
- Cooking oil
- Human waste
- Hygiene products
- Dead animals
- Chemically treated lumber (the chemicals in treated wood can leach into the compost and subsequently the soil, harming it)
- Dairy products
- Cellophane
- Leather goods
- Glass
- Bread and other baked goods
- Black walnut tree leaves and trimmings
- Plastic
In case you’re curious why you can’t compost parts of the black walnut tree, it excretes juglone, a toxin harmful to other plants. While excretion primarily takes place through its roots, juglone can also be found in the tree’s wood and leaves.
These toxins can spread across the compost and whatever’s treated with it, killing worms and other composters.
Adding black walnut tree to your composting pile essentially destroys the pile.
Materials to Think Twice About
While some materials are a simple “yes” or “no” for your compost pile, others sit in a bit of a gray area. Noxious weeds and insect-infest plants should normally be thrown out, but if you’re using a hot compost pile, then they can be composted.
Certain food scraps, while compostable, cause odors and attract pests to your pile. For example, in great amounts onions and garlic may produce unwanted effects, but in moderation it’s fine to compost them.
Pests can damage your composter trying to access and eat the materials, which makes maintaining your compost heap more hassle than it’s worth. Throw out this food waste if you don’t want to attract pests.
Citrus fruits, such as oranges and lemons, are very acidic. You can technically compost citrus peels and other parts of citrus fruits, but you may want to do so in moderation to avoid a high acidity in your compost.
Another item you might want to avoid composting is fruit and vegetable seeds. If your compost pile gets hot enough, plant seeds will naturally die, but if it doesn’t, you may end up with sprouted plants in your compost, which could inconveniently spread to whatever you apply your compost to.
How to Compost at Home
Beyond a composting bin and organic waste, home composting requires few up-front resources. Most types of composting bins don’t need too much regular maintenance, either.
The most complicated part of composting is getting the right mix of brown and green materials. These supply carbon and nitrogen to the compost pile, respectively. Carbon serves as a building block and energy source for microorganisms while nitrogen ensures these microbes can grow and function.
The ideal mix is 30 parts carbon-rich material for every 1 part nitrogen-rich material. Carbon-rich brown materials comprise paper, wood branches, dry leaves, and more. Green materials are nitrogen rich and include coffee grounds and other food waste. If you notice that your compost pile is particularly wet or full of fruit flies, it’s a sign that your ratio is off and you need more brown materials.
To compost at home, you’ll need to follow a specific formula:
- Select your compost materials.
- Store your waste. (In the fridge or freezer is best, to avoid bugs.)
- Choose a place to make compost and install your compost bin.
- Add the materials and mix.
- Wait and aerate.
- Harvest the compost once it looks like dark soil.
Buying vs. Building a Compost Bin
Buying a compost bin can be expensive, but it’s not your only option. Building a compost bin is quite simple. While you can read my guide to making your own compost bin with wooden pallets, the basic steps are easy:
- Get the right materials.
- Cut pallets to size and add chicken wire to the sides.
- Add chicken wire and a weed barrier to the bottom.
- Connect the four sides to the bottom.
- Add the top with a hinge so you can open and close it easily.
What Not to Compost: Wrapping Up
Dairy products, coal or charcoal ash, pet waste, glossy paper, and multiple other materials shouldn’t be composted. Plenty of items in your home are safe to compost, and a few even fall into a gray area, for which you should use your best judgment.
Avoid the obvious ones and put on your thinking cap to ensure your compost heap stays healthy and the finished compost is as nutrient-rich as possible.