9 Surprising Things You Should Compost—and 10 You Shouldn't

Making your own compost is one of the most effective ways to reduce waste and build healthy soil. But in order to get started, you must first know what items you can and can't compost. Adding the wrong things to your compost pile can attract insects, slow decomposition, or introduce harmful chemicals. While some items, like vegetable scraps, are known to be great additions to compost, there are some unexpected things experts say you can and can't add to your compost pile.

Surprising Things You CAN Compost

When making your own compost, consider adding some of these surprising items.

Wine Corks

Natural wine corks can contribute to the structure and aeration of your compost, says Misti Mathis, co-owner of Harvest Gold Organics. They may take a long time to break down, though, so it's best to grind them up before adding them to your compost pile. "Beware of imposters—synthetic, non-compostable corks can look almost identical to natural corks and shouldn't be added to compost," says Mathis.

Coffee Grounds and Filters

While many gardeners already know that coffee grounds are compostable, it may come as a surprise that you can also compost the filter. "Coffee grounds add nitrogen for healthy plants, while both grounds and filters attract microbes that power up decomposition in your compost," says Mathis.

Hair and Pet Fur

The next time you clean out your brush or the brush you use to groom your pets, toss the hair into your compost pile rather than throwing it away. "Hair and pet fur break down slowly, adding nitrogen and improving aeration in compost," says Mathis.

Used Napkins and Paper Towels

So long as there isn't any grease or chemicals on them, used napkins and paper towels are compostable. "Used paper towels add carbon for balance and break down readily in compost, providing both structure and brown material," says Mathis.

Old Herbs and Spices

Save old herbs and spices to use in your compost pile. These ingredients break down quickly, adding nutrients and attracting beneficial decomposers to your compost, says Mathis.

Natural Fabrics

Natural fabrics, like cotton and wool, add nitrogen and improve the overall structure and aeration of your compost pile as they decompose, says Mathis. Just make sure they are made from 100 percent natural materials and don't contain any synthetics.

Yeast

Do you have leftover yeast from a recent baking project you're not sure what to do with? Sprinkle it into your compost. "Yeast acts as a decomposing accelerant in compost, introducing microbes that break down organic matter faster," says Mathis.

Aquarium Plants

Aquarium plants, like those in your fish tank, are nitrogen-rich green material that are perfect for balancing your compost pile. Just make sure they are completely natural and not mixed with any plastic material first, says Java Bradley of Java's Compost.

Surprising Things You CAN'T Compost

Avoid adding these items to your compost pile.

Certain Tea Bags

Some tea bags have plastic in them and should never be added to your compost pile. "They don't break down and can contaminate your compost with micro-plastics," says Mathis.

Compostable Plates and Utensils

Some compostable plates and utensils aren't suitable for backyard composting. "Backyard composters don't usually achieve high enough temperatures in their piles or tumblers to break down these types of materials," says Bradley. "At a commercial composting facility, temperatures reach 131 degrees or higher over a sustained period of time which will break down these materials."

Cat or Dog Waste

While cat or dog waste is an organic material that will decompose, it still isn't something you should add to your compost pile. "Cat and dog waste is a no-go for composting because it can harbor parasites and pathogens harmful to humans and plants, even after composting," says Mathis.

Meat, Fish, and Bones

While these items will eventually break down, they take a long time to do so and shouldn't be added to compost. "The risk with composting meat, fish, and dairy is that it takes longer to break down, so if you have an open pile in your backyard it will attract animals," says Bradley.

Chemically Treated Plant and Law Trimmings

If your lawn and plants are chemically treated, avoid adding the trimmings to your compost. "Pesticides in plant trimmings can harm the beneficial microbes that break down your compost and potentially leave residues in the finished product, harming your plants," says Mathis.

Treated Wood

Similar to treated plant and lawn trimmings, you also shouldn't add treated wood to your compost pile. "Treated lumber contains chemicals like arsenic or copper that can leach into your compost and contaminate it, harming plants and potentially introducing toxins into the soil," says Mathis.

Coal or Charcoal Ash

Coal and charcoal ash from a fire or grill can raise the pH of your compost too high, making it inhospitable for many plants that prefer slightly acidic soil, says Mathis.

Oil and Grease

Oils and grease can smother decomposing materials, reduce oxygen, and slow down decomposition when added to compost. "They also create a greasy mess that can be difficult to manage in a compost pile," says Mathis.

Bread

While bread does break down in a compost pile, it's best to avoid using it as it can attract pests like rodents and mold due to its high starch content. If you have leftover bread you really don't want to throw away, it's best to compost it in small amounts or tear it up and bury it deep in the pile, says Mathis.

Toxic Plants

Do research on the plants growing in your garden before adding them to your compost. Toxic plants, like certain hemlock varieties, may not break down entirely and could harm plants or animals that come into contact with the finished compost, says Mathis.