Keep These 9 Things out of Your Compost Pile

You may have done plenty of research on what to toss in your compost pile, but have you ever thought about what to exclude? Time to break it down! Join gardener and home composter Lindsay Miller to find out what shouldn’t go in the compost pile.

Close-up of a gardener in grey gloves adding green garden waste, including weeds, from a white bucket to a large compost pile containing kitchen scraps.

Contents

Composting feels like magic. Throw your wilted lettuce, onion skins, fallen leaves, and other garden waste in a bin. Let it sit. Flip the pile with a shovel a few times, or give the tumbler a spin. TA-DA! Dark, crumbly, rich garden goodness is yours, ready to spread in your veggie bed or topdress your perennials.

It feels almost too good to be true. After scooping out that first batch of finished compost, you may start to wonder, “What else can I throw in there?”

Not everything belongs in the compost pile. Adding the wrong materials can attract pests, brew unpleasant odors, and even contaminate your compost with harmful substances. To ensure your compost remains safe and effective, it’s important to know what to keep out. Dig in, and let’s talk about what shouldn’t go in the compost pile.

Diseased Plants

Close-up of a man holding a diseased tomato plant with dry brown leaves and oval green fruits showing signs of rot.
Dispose of diseased plant material properly to prevent future infections.

Did you battle blight in your tomatoes this season? Maybe you fought fusarium wilt on your peppers? Well, guess what: Many viruses and fungal diseases persist happily in the soil or dead plant material for long periods of time.

Some plant pathogens and diseases even survive long winters. Tossing diseased plant material into your backyard bin is a surefire way to guarantee you’ll be seeing those same diseases next year after you spread your amendments back in the garden.

Many pathogens die at high temperatures. However, most backyard composting systems won’t reach and sustain the 130-150 degrees Fahrenheit necessary to eradicate disease.

What To Do Instead

Place diseased or infected plant material in a trash bag and dispose of it with trash headed for the landfill. Burying the infected plant debris outside the garden is also an option.

Burying will reduce the chance of spreading disease from debris to plants currently in the garden or to plants that will be in the garden the next year. Be sure to thoroughly disinfect any shovels, trowels, or pruners afterward.

Meat Scraps

Beef scraps appear as irregularly shaped chunks of meat and fat, reddish-brown with streaks of white fat and connective tissue.
To prevent odors and pests, avoid adding meat to the pile.

Let’s start by stating that meat and bones are biodegradable and will decompose. Eventually. Large chunks of protein-rich meat and bone can significantly slow down the decomposition process.

In the meantime, they smell quite unpleasant and can attract a ton of nuisance wildlife over to your compost bin. Rotten meat can also harbor harmful bacteria like E. coli and Salmonella. If these pathogens aren’t nuked properly, they are a food safety risk in your garden.

What To Do Instead

Meat scraps are best fermented in a Bokashi composter. Then, add the resulting Bokashi product to your backyard pile. Alternatively, dispose of meat in a heavy-duty trash bag with other household trash.

Dairy, Oil, and Grease

Close-up of fresh sliced ​​soft cheese in triangle shape next to glass jug filled with milk.
Avoid adding high-fat foods to prevent pests and odors.

Like meat scraps, cooking oils, grease, and dairy products can also attract flies, rodents, and other wildlife pests to your yard. They smell pretty bad when they decompose, and dairy products such as cheese, milk, and yogurt are particularly difficult to break down.

These foods have high fat content and a lot of moisture. They’ll need loads of dry, carbon-rich material (“browns” in compost-speak) like shredded cardboard and wood shavings to offset the large amount of nitrogen and moisture they add to the pile.

What To Do Instead

Dairy products can be composted in a hot composting system, ideally one that maintains an internal temperature of at least 130°F (54°C). At this temperature, most harmful bacteria and other pathogens are killed. However, these temperatures are fairly difficult to achieve in a backyard composting system.

Your best bet is to contact your municipal or other large-scale yard waste facility; most of these industrial facilities are capable of safely processing dairy, grease, and other fatty animal byproducts.

Treated Wood

Treated wood has a greenish tint with a smooth surface, showing visible pressure marks or chemical stains.
Add only clean, untreated wood to avoid harmful chemicals.

Wood is an excellent, carbon-rich ingredient. However, only clean wood, like branches, logs, and raw lumber that has never been painted or stained, should be added to the compost bin. Unless you cut it down yourself, it can be difficult to know the origin of many wood products.

Composting is based on the premise of decomposition, and pressure-treated lumber, plywood, and strand board are all treated with chemical compounds that actively prevent their decay. These chemicals can contain arsenic, chromium, and other toxic components that are dangerous to both human health and the environment.

You wouldn’t want these toxins to be added to your veggie bed next season, nor would you want them to leach into the ground below your pile. Keep these items out of the garden in general.

What To Do Instead

Check with your state’s environmental protection department before burning, as exact regulations may vary from state to state. Burning treated wood creates toxic fumes and is generally prohibited. Dispose of treated wood at a landfill. 

Weeds

Close-up of a gardener in blue pants with a pile of torn weeds in the garden.
As long as seeds are killed, some weeds are fine.

Ok, this one isn’t a strict no. As long as the roots and seeds are effectively killed, having some in your compost won’t be detrimental to your garden. Weeds are just “unwanted” plants – they’re still full of nitrogen and other nutrients valuable to compost. The exceptions are invasive plants, like Japanese knotweed or bamboo, which should not be added to a home compost pile. Read more on that below.

What To Do Instead

If you are able to regularly turn and manage your pile to achieve high temps, you may be able to successfully compost weeds. However, to be on the safe side (and save yourself a lot of weeding hours in the future), trim the seed heads before tossing them in. Fermenting small amounts of weeds in a Bokashi composter is another option.

Invasive Plants

Vinca minor is a low-growing plant with glossy, dark green leaves and small, violet-blue, star-shaped flowers.
Tossing invasive plants in the pile can spread new infestations.

I’m currently battling goutweed in a portion of our yard and can vouch for this invasive plant’s tenacity: even a tiny fragment is enough to sprout a whole new individual. Don’t toss invasive plants in the compost! One improperly decomposed bit of plant can kick off a new infestation in your garden.

As with diseased plant material, high temperatures are needed to effectively kill persistent invasive plant material. Small backyard compost piles rarely get hot enough to do so.

What To Do Instead

The best strategy in managing invasive plants is to halt their spread (and stop purchasing them from garden centers in the first place!). While you won’t want the invasive plant material in your home compost pile, it’s also incredibly important that the material doesn’t just get moved elsewhere. Tossing it in the nearby woods will just exacerbate the problem.

Kill the plant material onsite if possible, either by desiccation or solarization. Dead plant material can be buried, but it needs to be several feet deep in the soil, a potentially daunting task. If the material cannot be managed onsite, double bag it, including the roots, shoots, and seed heads, and dispose of it with your household trash.

Pet Waste and Litter

A green litter box filled with light brown, cylindrical wooden pellets, neatly covering the bottom surface.
Scoop and bag pet waste to protect your garden and environment.

Pet waste can be full of parasites and harmful bacteria that can find their way into your garden bed if not destroyed properly. Most backyard composting systems do not reach the high temperature necessary to kill off these pathogens.

Clean, unused cat litter can be composted, provided it is plant-based, like those made of wood or paper pulp. Scented litter and those containing sand or clay cannot be composted.

What To Do Instead

Scoop the poop! Pet waste left to accumulate on lawns can leach pollutants into streams and lakes. Scoop, bag and dispose of pet waste in the trash headed for the landfill. 

Wrappers and Packaging

The bananas are bright yellow with smooth skins, each adorned with a small, colorful banana sticker near the middle.
Avoid adding non-biodegradable packaging to your pile.

This one seems like a no-brainer, but speaking as someone who has pulled my fair share of banana stickers out of our bin, I can attest that food packaging can show up in surprisingly sneaky ways.

Nonbiodegradable items like produce labels, staples from tea bags, and wax-coated cardboard containers should not go in the compost pile. Plain, unmarked coffee filters and tea bags can be composted but they should be shredded first.

What To Do Instead

Paper, glass, and certain plastics can be recycled. Be sure to rinse food cartons thoroughly, and check your municipal recycling guidelines if you are unsure about what they’ll accept. Many states and municipalities will have universal recycling programs that accept all items together, however some areas require paper, glass, and plastic to be separated.

“Compostable” Tableware and Bags

Eco-friendly food packaging includes cardboard cups, boxes, plates, cutlery, bags, and packages, all in natural brown tones, arranged on a light gray background.
Choose reusable or certified biodegradable tableware for better disposal.

In a case of flawed advertising, plates, cutlery, and bags listed as “compostable” are typically not compostable in a backyard compost pile. High temperatures are needed to break down many of these materials.

Most residential systems, and even some municipal composting facilities, just cannot guarantee complete degradation of these products. One study revealed that a particular type of “biodegradable” bag failed to decompose even after being buried in soil for 3 years. An exception? Utensils or plates made of completely untreated wood.

What To Do Instead

Look for products verified by the Biodegradable Products Institute (BPI), which provides technically and scientifically credible certifications for materials that actually biodegrade in the environment. Consider using reusable tableware and cutlery, which can simply be washed and reused. 

Final Thoughts

This might feel like a long list of items not suitable for the compost bin but don’t worry, there are plenty of suitable materials to feed your compost pile. Ultimately, you just need to exclude items that are particularly attractive to wildlife or pose a hazard to human or environmental health. By being aware of these exclusions, you can create a fantastic, nutrient-rich amendment that supports a thriving and sustainable garden.

Share This Post
sterilize compost. Close-up of a man's hand pouring a pile of compost from his palm against a blurred green background. Compost, the end product of the decomposition process in a compost pile, is characterized by its dark, crumbly texture and earthy aroma. Compost is composed of decomposed organic matter such as kitchen scraps, yard waste, and plant material, broken down by microorganisms and other decomposers over time.

Composting

Should I Sterilize Compost Before Use?

If you’ve had problems with plant diseases, you may think putting compost in the oven or microwave is a quick fix cure. Sterile means pathogen-free, right? Well, things are a bit more complicated than that. Former organic farmer and soil expert Logan Hailey explains the nuances of home-sterilizing compost and the science behind pathogen-free compost.

Gardener holding composting worms.

Composting

The Best Worms for Composting

Choosing the right worms is essential to successful worm composting. Learn what types of composting worms work best in your worm bin and why you can't use regular garden worms to recycle organic waste in this guide by Urban Worm Company Founder and worm expert Steve Churchill.