What to Compost and What to Avoid Putting in Your Pile
Book: Backyard Farming: Composting | Author: Kim Pezza | ISBN: 978-1-57826-587-9 | Hatherleigh Press, 2015
So you’ve got a bin or a pile set up. Now comes the question everyone asks: what actually goes in there? Chapter 5 of Pezza’s book breaks it down into two categories you’ll hear about constantly in composting. Greens and browns. Plus a solid list of things that should never touch your pile.
Greens (Nitrogen)
Greens are your nitrogen-rich materials. Think protein. These are the things that break down fast and generate heat in your pile.
The obvious stuff: fruit and vegetable scraps, bread, pasta, coffee grounds and filters. But the list goes way beyond your kitchen. Alfalfa, clover, garden waste, grass clippings, hedge trimmings, seaweed, manure, and crushed egg shells all count as greens.
Hay is technically a green, but some composters argue about it because it can carry weed seeds into your pile. Worth knowing before you toss a bale in there.
Weeds can go in too, but only if they’re past their seed stage. If they’ve already gone to seed, you’re just planting weeds in your future garden. Not ideal.
Here’s one that surprises people: moldy food is totally fine for composting. That fuzzy bread in the back of your pantry? Toss it in. Old spices that lost their flavor three years ago? In they go. The mold is already doing decomposition work for you.
A Note About Lime
There’s an old gardening trick where people add lime to their compost pile. Pezza says hold off on that. Lime can actually reduce nitrogen in your pile, which slows things down. Some gardeners only add lime if there’s a specific pH problem, and even then they add it to the finished compost rather than the active pile. Unless you’ve tested your compost and found a pH issue, skip the lime.
Browns (Carbon)
Browns are your carbon-rich materials. Think carbohydrates. These provide structure, absorb moisture, and keep your pile from turning into a wet, smelly mess.
The easy ones: paper, junk mail, paper egg cartons, dried leaves, and small amounts of cardboard. Newspapers work great too. Shred everything first for faster breakdown.
Then there’s the bigger stuff: bark, sawdust, corn and vegetable stalks, pine needles, straw, and twigs. Break twigs into small pieces or they’ll just sit there for months doing nothing.
Some browns you might not think of: chicken feathers (chop them up first), hair from your brush (scatter it through the pile, don’t drop it in a clump or it’ll mat together), chopped leather, and crushed nut shells.
Sod can go in your pile, but only if the pile is running hot enough to kill the grass roots. Otherwise you’ll end up with grass growing out of your compost heap, which is not the look you’re going for.
Wood Ash
Wood ash deserves its own section because it’s useful but tricky. It adds phosphorus, potassium, and micronutrients. But use it sparingly because it’s highly alkaline and can throw off your pile’s pH balance.
Important: only use ash from fireplace or campfire logs. Never use charcoal ash or ash from treated wood. And be careful with fruit wood ash. Fruit trees are often sprayed with chemicals, and those chemicals survive the burning process and end up in your compost. Not what you want in your garden soil.
Neutral Additions
Rinse water from your dishes and old beverages can go in the pile for moisture. Just don’t overdo it. Your pile needs to be damp like a wrung-out sponge, not soaking wet.
What NOT to Compost
This list is just as important as the greens and browns. Put any of these in your pile and you’ll either ruin your compost, attract unwanted visitors, or spread disease to your garden.
- Coal ash contains sulfur and iron that damage plants
- Colored paper and cardboard can contain toxins from the dyes
- Diseased plants will spread disease to your garden if your pile doesn’t get hot enough to kill the pathogens
- Inorganic materials and treated lumber don’t break down and leach chemicals
- Synthetic chemicals of any kind
- Meat, bones, fish, dairy, and fats attract animals, cause terrible odors, and can overheat your pile
- Rice becomes a breeding ground for harmful bacteria
- Cat litter and dog waste carry bacteria, parasites, and pathogens that are dangerous to humans
The Black Walnut Warning
This one is specific but serious. Black walnut trees release a chemical called juglone. It kills blackberries, tomatoes, potatoes, blueberries, and apple trees. If juglone gets into your compost and then into your garden, those plants are done.
Some gardeners do compost black walnut leaves, but Pezza recommends testing first. Put some of the finished compost around a tomato seedling and see what happens. If the seedling dies, your compost has juglone in it and should stay far away from sensitive plants.
How to Add Materials to Your Pile
Keep a kitchen compost pail or a 5-gallon bucket with a cover near your prep area. When it’s full, take it out to the pile. If you can’t get to the pile right away, you can store scraps in a sealed bag in the fridge for a day or two.
When you’re starting fresh, alternate layers of brown and green materials. Once the composting process gets going, you can just dump new stuff on top without worrying about perfect layers.
How much brown versus green? Opinions vary. Some people say equal amounts. Others say use twice as much brown as green. What everyone agrees on is this: too much nitrogen (greens) makes a slow, smelly pile. When in doubt, add more browns.
Always chop or shred materials before adding them. Spread everything out in the pile. Don’t dump things in a big clump or they’ll mat together and decompose unevenly.
Composting Leaves Separately
If you’ve got more leaves than your main pile can handle, compost them on their own. Find a shaded spot, pile them up about 4 feet in diameter and 3 feet high, and let them sit. It takes about 6 months.
The result is a great soil conditioner, but it’s not fertilizer. It improves soil structure and water retention without adding significant nutrients. Still very useful, just different from regular compost.
What’s Next
Now that you know what goes in and what stays out, the next post covers composting on a larger scale with livestock materials.