While most kitchen and food waste are safe to compost, there are a few you shouldn’t add to a compost pile. Some of these include citrus peels, onions, plants treated with pesticides, feces, meat scraps, treated woods, tea bags, black walnut tree debris, coal ash, and sanitary products.
Despite the long list of organic materials you can compost at home, some shouldn’t go in your compost pile.
This is because they may contain pathogens and other dangerous substances that can contaminate water, soil, or even the plants you’re growing.
What’s more, some organic materials might not break down, thus slowing decomposition and attracting unwanted animals such as raccoons, rats, and stray dogs.
To help you generate better compost, we’ve rounded up a list of what not to compost and a bonus list of intriguing items you probably didn’t realize you could compost.
Table of Contents
What Not To Compost
1. Citrus Peels, Onions, and Garlic Scraps
Adding citrus peels, onions, or garlic scraps to your compost pile is not advisable because they contain natural chemicals and high acidity levels. As a result, they can kill worms and other beneficial microorganisms that aid in breaking down organic matter in the soil.
But, if you must use these materials for your compost, chop them into small pieces to hasten decomposition.
Extra Tip: Instead of throwing away the onion scraps, you can freeze them for future recipes and use citrus peels for a DIY candied peel.
2. Plants Treated with Pesticides or Preservatives
Plants or grass clippings treated with heavy pesticides, fungicides, or herbicides can harm your compost pile, putting you and the environment at risk. These harmful chemicals can contaminate water supplies, soil, and edible plants.
Also, don’t compost treated, varnished, stained, or painted wood.
3. Human or Animal Feces
Even though some animal manure is used for composting, animal feces and urine from carnivores are unsuitable for your compost. For example, cat feces and dog poop contain pathogens and viruses that cause human disease.
Not only that, but these materials may also attract rodents and other animals that can spread the pathogens further.
Cat litters are to be avoided because they contain organisms that cause toxoplasmosis.
On the other hand, human feces carry parasites and pathogens that pose a health risk and leave your compost ineffective.
However, you can use properly composted human feces for growing flowers.
4. Fish and Meat Scraps
Fish and meat scraps are organic materials that can add nutrients to your vegetable garden. However, when fish and meat remain rot, they emit a foul smell, attracting flies, rats, raccoons, mice, and other pets.
Would you rather have these pests infest your yard or deal with pet waste? Definitely, not.
And again, the stench of rotting fish and meat products can be quite nauseating.
If you still want to try and compost meat scraps, check out our guide on how to do that.
5. Sawdust from Treated Wood
Although sawdust from treated wood—painted, pressure treated, stained, or varnished—is an organic material, it’s not something you should add to your compost pile.
Saw dust from treated wood contains toxic chemicals (arsenic and cadmium), which affect microorganism activity, slowing decomposition. If consumed, these compounds are similarly harmful to human beings.
6. Coffee and Tea Bags
Tea leaves and coffee grounds contain a good amount of nitrogen, potassium, and phosphorous essential for plant growth.
However, to compost coffee grounds and tea leaves, you need to remove them from their bags. The bags are made of synthetic fiber and nylon, which don’t decompose.
Wondering what type of tea bags you can compost? I wrote an article on this topic, which you can find here.
7. Black Walnut Tree Debris
Black walnut roots, leaves, and twigs contain a naturally occurring compound (Juglone) that hinders growth or even kills them (especially in high concentrations).
It affects ornamental plants like azalea, hydrangea, viburnum, and food crops such as potatoes, tomatoes, and pepper.
8. Coal Ash
Adding coal ash or charcoal ash to your compost bin should be a no-no. These ashes contain high levels of sulfur which is bound to increase soil acidity and harm your plants.
Furthermore, charcoal briquets may contain chemicals harmful to both plants and people.
9. Diseased Plants
Diseased or insect-infested plants contain pathogens (fungi and bacteria) that can cause serious problems for you and your garden.
It’s important to note that pests and diseases can survive the composting process because the temperatures employed in home compost bins are not high enough to destroy them.
10. Dairy Products
Adding dairy products such as butter, milk, cheese, and yogurt to your compost pile will only create an unpleasant odor and attract flies, rodents, and other unwanted pests.
Not to mention, these processed products contain fats that don’t easily decompose.
If you are still set on trying to compost cheese, here’s a step-by-step guide on how to do it.
11. Used Personal Products
Hygiene products such as sanitary napkins, diapers, tampons, wipes, or items soiled in human fluids shouldn’t be composted because they can cause health problems.
However, if 100% biodegradable, there is a way to compost tampons. Check my how-to guide.
12. Sticky Labels on Fruits and Vegetables
Sticky labels on fruits and vegetables can get stuck to the compost pile, slowing down the decomposition process.
And, since these stickers are made of plastic or vinyl, they may also contain harmful chemicals.
13. Cooking Oil
Don’t add cooking oil to your compost pile because it’ll slow the composting process. Cooking oil contains some chemicals which might interfere with the balance of nutrients in the compost heap.
In addition, oils can form a water-resistant barrier preventing water absorption. It also has a smell that attracts insects and pets.
14. Coated or Glossy Paper
Most paper products such as paper towels, tissues, newspapers, and shredded cardboard are compostable materials.
But, when they’re coated, they don’t break down easily and may produce toxins harmful to plants.
To increase the nutrients in a finished compost pile, you can add bread products such as pasta, cakes, or bread.
15. Bread and Baked Goods
However, they’ll produce a foul smell, inviting unwanted pests into your yard.
Other things you shouldn’t compost include:
- Dead animals
- Leather goods
- Lawn trimmings treated with chemicals
- Cigarette butts
- Large branches
- Torn or shredded clothing
- Inorganic and non-biodegradable materials
BONUS: Things You Did Not Know You Can Compost
Now that you’re aware of some of the household and food scraps you shouldn’t add to the compost pile, here are a few compostable items you may not have realized you can recycle into usable nutrients for your garden:
- Dyer lint
- Aquarium plants
- Hair and fur
- Herbs and spices
- Wooden toothpicks and chopsticks
- Unpopped popcorn
- Uncoated cardboard and paper plates
- Home Brewing Waste
How to Remember What Not To Compost
If you want to remember what not to compost, you’ll need to ask yourself the following:
- How long the material takes to decompose?
- Can the item transmit bacteria, fungi, and plant diseases?
- Does it cause an imbalance of nutrients in the soil?
So whether you’re new to composting or want to ensure you’re doing things the right way, taking these precautions will help keep your garden healthy.