Let’s be honest—composting feels like magic. You toss in your kitchen scraps, stir the pile every now and then, and boom: rich, dark soil that makes your plants thrive. But here’s the thing I didn’t realize when I started: not everything belongs in that magical heap. Some items can attract pests, spread disease, or even ruin your compost entirely.
Preferences vary—some gardeners swear by citrus peels, others avoid them like the plague. Some love coffee grounds; others worry about acidity. I get it. But when it comes to things to not compost, there are clear lines even the most flexible composter should respect.
I’ve been composting for over a decade, mostly in my backyard in central Florida. Over the years, I’ve made mistakes—like tossing in meat scraps during a heatwave (hello, raccoon invasion) or adding glossy magazine pages (toxic ink city). Those lessons shaped this guide.
In this article, I’ll share exactly what doesn’t belong in your compost bin, why it’s harmful, and what to do instead. Whether you’re a beginner or a seasoned composter, these insights will help you build healthier soil—and avoid the stinky, slimy disasters I’ve lived through.
Why Knowing What NOT to Compost Matters
Composting is all about balance. You need the right mix of greens (nitrogen-rich) and browns (carbon-rich), moisture, and airflow. But throwing in the wrong materials throws that balance off—sometimes dangerously.
Some items break down too slowly, others release toxins, and a few can even introduce pathogens that survive the composting process. I once added diseased tomato plants to my pile, thinking the heat would kill the blight. Spoiler: it didn’t. My entire garden got infected the next season.
Knowing what not to compost isn’t just about avoiding mess—it’s about protecting your garden, your health, and the environment. Let’s dive into the specifics.
Top 10 Things to Not Compost (And Why)
1. Meat, Fish, and Dairy Products
I used to think, “It’s organic, right? It should compost.” Wrong. These items decompose slowly and produce foul odors that attract rodents, raccoons, and flies. Worse, they can harbor harmful bacteria like E. coli and Salmonella.
Instead: Dispose of these in the trash or use a bokashi system if you’re serious about fermenting food waste.
2. Oily or Greasy Foods
Grease from cooking, salad dressings, or fried food might seem harmless, but they create anaerobic pockets in your pile. That leads to sour smells and slows decomposition.
Instead: Scrape plates into the trash before composting veggie scraps. A little oil on veggie peels? Probably fine. A greasy pizza box? Toss it.
3. Pet Waste (Especially Dogs and Cats)
I love my dog, but his poop doesn’t belong in my compost. Pet waste can contain parasites like Toxoplasma and Giardia that survive composting and can infect humans.
Instead: Flush it (if safe in your area) or bag and trash it. Some municipalities offer pet waste composting programs—check locally.
4. Diseased or Insect-Infested Plants
Burn or bag these. Composting doesn’t always reach temperatures high enough to kill pathogens or pests. I learned this the hard way with powdery mildew on my zucchini.
Instead: Remove infected parts immediately and dispose of them away from the garden.
5. Weeds That Have Gone to Seed
Weeds like crabgrass or chickweed can spread if composted before seeds die. Even hot compost piles might not kill all seeds.
Instead: Dry them in the sun for a few weeks before composting, or toss them in the trash.
6. Treated Wood or Sawdust
Pressure-treated wood contains arsenic and other chemicals. Burning or composting it releases toxins into your soil.
Instead: Use untreated wood chips as mulch, but never compost treated lumber scraps.
7. Glossy or Colored Paper
Magazines, flyers, and gift wrap often use toxic inks and coatings. These don’t break down safely and can leach heavy metals.
Instead: Recycle plain paper. Use shredded newspaper (black-and-white only) in small amounts as a brown layer.
8. Coal or Charcoal Ash
Barbecue briquettes may contain additives that harm plants. Even natural charcoal can raise soil pH too high.
Instead: Use wood ash sparingly (from untreated wood fires) and only if your soil is acidic.
9. Synthetic Materials (Plastics, Fabrics, etc.)
Plastic-coated tea bags, synthetic fabrics, or “biodegradable” plastics labeled as compostable often aren’t backyard-compostable. They break into microplastics.
Instead: Use loose-leaf tea or compostable bags certified for home composting (look for BPI or TÜV labels).
10. Human Waste
This one’s a hard no unless you’re using a specialized humanure system with strict safety protocols. Regular compost piles don’t get hot enough to sterilize pathogens.
Instead: Stick to toilet systems designed for composting human waste, and follow guidelines carefully.
Composting Safely: My Personal Tips
After years of trial and error, I’ve developed a few habits that keep my compost healthy and pest-free:
- Chop it small: Smaller pieces break down faster and reduce odor risks.
- Layer greens and browns: Aim for a 1:3 ratio of greens (food scraps) to browns (leaves, paper).
- Turn the pile weekly: Aeration prevents anaerobic conditions and speeds decomposition.
- Keep it moist, not soggy: Like a wrung-out sponge—too wet, and it stinks; too dry, and nothing happens.
- Monitor temperature: A hot pile (130–160°F) kills weed seeds and pathogens. Use a compost thermometer.
I also keep a small countertop bin for daily scraps—just fruit and veggie peels, coffee grounds, and eggshells. Nothing oily, nothing meaty. Simple.
What About “Maybe” Items? My Honest Take
Some items are borderline. Here’s how I handle them:
- Citrus peels: They’re acidic, but in small amounts, they’re fine. I compost them, but not in bulk.
- Onion and garlic scraps: Some say they inhibit microbial activity. I add them sparingly—no issues so far.
- Tea bags: Only if they’re 100% paper or compostable. Many have plastic threads or staples.
- Cheese rinds: Hard, dry ones? Maybe. Soft, moldy cheese? No way.
When in doubt, I ask: “Will this attract pests? Harm microbes? Spread disease?” If yes, it stays out.
Key Takeaways
- Never compost meat, dairy, oils, pet waste, or diseased plants.
- Avoid glossy paper, synthetic materials, and treated wood.
- Hot composting helps, but it’s not foolproof—know your limits.
- When unsure, err on the side of caution. Healthy compost starts with smart choices.
FAQ: Your Composting Questions Answered
Can I compost eggshells?
Yes! Rinse them to remove residue, crush them, and add them. They add calcium and help balance acidity.
What about bread or pasta?
In small amounts, yes—but they can attract pests. Bury them deep in the pile and avoid if you’ve had rodent issues.
Is it safe to compost walnut shells?
Black walnut shells contain juglone, a compound toxic to some plants. Compost them separately and use only on tolerant plants like tomatoes or corn.
Final Thoughts: Compost with Care
Composting has taught me patience, observation, and respect for nature’s cycles. It’s not just about recycling waste—it’s about building life from decay. But that process only works when we give it the right ingredients.
I’m still learning. Every season brings new challenges—like the time I accidentally composted a plastic plant tag (oops). But each mistake makes me a better gardener.
If you’re just starting out, don’t stress. Start small, avoid the big no-nos, and watch your pile transform. And if you’ve got a composting horror story, I’d love to hear it—drop a comment below.
Thanks for reading, and happy composting! 🌱