Great compost is made from decomposed carbon-based ingredients under oxygen-rich conditions. While the process involves a harmoniously complex community of microorganisms, the ingredients for making great compost are simple.
Greens, browns, and water are all you need to make great compost. Green materials provide nitrogen-rich food for bacteria, while brown materials provide food and structure for fungi. Water then delivers dissolved oxygen to the entire operation. Read on for more details on what you can contribute to your local compost bin.
Compost safe materials
Green materials
Think of your average vegetarian friend. Their diet might consist of leaves, nuts, and berries. The microorganisms that thrive in compost enjoy many of those same foods. Generally, most plants are decomposable down to their simplest and nitrogen-rich components. Bacteria will use this nitrogen and a small amount of carbon to grow, multiply, and generate heat. The cycle of bacteria consuming and multiplying is what helps make compost warm to the touch. Here are some items that make for good sources of nitrogen.
Fruit/Vegetable scraps
Uncooked food and raw vegetables are acceptable for composting. Think of lopped-off onion ends, grassy strawberry tops, and papery potato skins. If you cook at home often, it’s easiest to keep a bucket or a cardboard box of scraps in the freezer to store until it fills up. It is best to avoid adding cooked food due to its high salt content.
Yard Waste
Green leaves, fresh grass clippings, and plucked weeds make for great composting scraps. When composting yard waste, separate the green leafy material from the brown woody material. Prioritize leafy greens for their nitrogen content and chop them up with shears when adding them to the pile.
If weed seeds are of concern, the compost must reach an internal temperature of () to destroy most weed seeds. It is generally best to add weeds before their seed heads have formed, but if you must, make sure to bury any seed heads as close to the pile’s hot middle section.
High Nitrogen Party foods
Animal manure (from herbivores)
Animal manure, although brown to the eyes, is still considered “green” in the composting world due to its exceptionally high nitrogen content. Specifically, manure from herbivorous livestock is preferred as long as it does not contain pesticide residues from their diet. Dried livestock manure is easiest to work with and helps avoid adding too much moisture to the pile. Believe me, A waterlogged and anaerobic pile full of manure is the last thing you want.
Avoid adding waste from carnivorous animals. (cats, dogs, etc.) Carnivorous pet waste is more likely to harbor disease-causing pathogens that could contaminate your food. Their waste also contains proteins that will slow down the decomposition of your bin.
Legumes (a.k.a. Beans)
Plants from the legume family are positively packed with nitrogen. Legumes form symbiotic relationships with particular bacteria that boost nitrogen uptake by the plant. This is why some savvy farmers will plant legumes as cover crops in between their cash crops. You’ll find the most useful nitrogen in a legume’s fruit and flowers. Chop up those bean pods (or the whole plant if necessary) and place them at the center of the pile for a hot and fast kickstart to the compost.
Brown Materials
The same beneficial fungi that help exchange nutrients and water with your food crops go crazy for any woody plant material you add to the compost. They might not break down quickly like green bacterial food, but brown materials feed soil fungi and provide structure to the soil, which facilitates oxygen delivery deeper into the pile.
Sourcing brown materials for composting is simple, especially in the fall season. Keep Fall in mind because this category means hunting for crunchy leaves, brittle branches, and even shredded cardboard. Most items that make for good bonfire fuel fall into this category.
For example:
- Cardboard boxes
- Printer paper
- Newspaper
- Chipped untreated wood
- 100% cotton clothing
- Dead leaves
- Used coffee grounds
- Old homework
- Junk mail (no plastic screens, please)
Just like green materials, make an effort to shred your brown scraps into smaller pieces before adding them to the pile. Cardboard should be shredded, twigs can be broken up, and tree trunks should be mulched/dried. Smaller pieces provide a larger surface area for microorganisms to latch onto. This also helps your browns break down into coveted organic carbon faster.
Materials to avoid
Cooked food
Avoid using cooked food for composting because the seasonings from that food will make the compost too salty and/or too spicy for the local beneficial microorganisms to thrive. If you’re a good chef, the smells of your leftover culinary creations might also attract scavenging pests that don’t mind digging through your compost to find an easy meal.
Meat and dairy products
Meat is a compostable material, but I would not recommend adding it to any residential composting project. Decomposing meat tends to carry a very foul stench, which attracts flies that create maggots, which grow into more flies that help spread pathogens as they fly around… gross. The same goes for many dairy products. Oftentimes, they do not decompose fast enough before they begin to rot and emit odors, so it is best to stick to vegetable scraps and paper.
Plastics
At any cost, do not feed your compost plastic. This includes paper/cardboard with a glossy coating. Plastics may become brittle and break off into smaller pieces over time, but they will never truly decompose in your soil. The soil food web is only capable of using organic carbon-based material, so if you ever find plastic in the compost, remove it. Otherwise, you can expect to see that odd plastic spoon from last season persist into the next season, and the next, and so on…
Fresh Manure
Any manure, especially fresh manure, should be treated as a biohazard. Fresh manure carries a higher load of active bacteria and potentially disease-causing pathogens. Drying the manure decreases its water content, giving it a longer shelf life if it needs to be stored for later use. Drying also puts many of the microbes occupying that waste into dormancy or it destroys them. Overall, this makes your pile safer to work with.
Manure from carnivores
Carnivore waste is not good for the compost because their waste can harbor diseases that are transferable to humans. For example, cat waste can contain parasitic eggs which can cause toxoplasmosis, a disease that evokes flu-like symptoms in humans.
Closing Remarks
Compost, when made anaerobically, can offer many health benefits to both your plants and the soil they grow in. Green materials feed bacteria and carry higher loads of nitrogen, which comes from fruit/vegetable scraps. Brown materials, like newspaper and wood chips, feed beneficial fungi and contain more carbon.
When mixing everything together, I would recommend adding the components in layers. Take care to add high-nitrogen materials, like legumes and simple sugars, toward the middle of the pile. This will encourage a surge of bacteria to grow, followed by an increase in fungal hyphae as the pile is left to mature.
The last ingredient for making good compost is water. Life, including microscopic life, needs water to survive. A good compost pile should be kept damp, but not moist. Maintaining ideal moisture in a compost pile will make for quicker decomposition and a biologically rich final product.
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