Organic material makes up approximately one-third of all material sent to landfills. Composting reduces the amount of garbage produced and creates a useful, garden-enhancing product from kitchen and garden waste.

There are two types of compost material: green and brown. Green items are nitrogen-rich materials such as kitchen scraps, fresh-cut grass, feathers, hair, and manure, whereas brown materials are dry, carbon-rich items such as shredded paper and cardboard, dried leaves and grass, peat moss, sawdust, cornstalks and cobs, and straw. Alternating layers of greens and browns will increase the likelihood of developing successful compost in a relatively short time.

Ideally, you should start with a base layer (6-10 cm) of brown materials to facilitate air circulation. Collecting and storing fall leaves is a good way to ensure a year-round supply of carbon-rich material that can be layered into the compost as needed.

Items to add to your compost

The following household and garden materials are compostable:

Coffee grounds and filters

Dryer link (if your clothes are made from natural fibers)

Egg shells (rinsed and crushed)

Feathers and hair (don’t add any that have been coloured using chemicals)

Fireplace ashes (don’t use ashes from chemically treated wood)

Grass

Leaves

Old potting soil

Plants (don’t use weeds that have gone to seed, as you may end up adding viable weed seeds to your garden with the finished compost)

Sawdust (don’t use sawdust from chemically treated wood)

Shredded paper and cardboard (use only uncoated paper that is free of toxic inks and grease)

Straw

Tea bags

Vegetable and fruit trimmings (and rotten produce)

Chop or shred compostable materials to small pieces and layer wet and dry items. Keep the layers varied rather than adding thick layers of any one ingredient.

The microorganisms that will convert your garbage into compost require oxygen. This is why compacted materials in landfills take ages to decompose, and why they produce methane (a greenhouse gas) in the process. To avoid these problems, leave a little space for air in the compost bin and turn the materials over once a week (or at least every 2 weeks) to mix and aerate them.

What you should not put in your composter

There are a number of kitchen items that will cause the compost to smell foul and attract rodents and other pests. Such materials, which are also very slow to break down in the composter, include:

Baked goods (breads, cakes, muffins, etc.)

Dairy products

Grease/oil/fat (and paper towels contaminated with oily substances)

Meats/poultry/fish/bones

Pasta

Rice

Sauces and salad dressings that contain fats, oils, dairy, or meat

Items that shouldn’t be composted due to their toxic content include:

Ash from coal or barbecues

Chemically treated wood products

Glossy coated paper

Medications

Most types of kitty litter

Metallic wrapping paper

Other items that can be harmful if composted include seeds of aggressive weeds, which will later grow in the garden after the compost is used, and diseased plants, as there is a risk of spreading disease back to new plants when the compost is used.

Should you compost pet waste?

Although manure from vegetarian pets (cows, sheep, horses, gerbils, guinea pigs, rabbits, etc.) is considered safe for composting, manure from meat-eating pets such as cats and dogs can be problematic due to the risk of spreading zoonotic diseases (illnesses that can be transmitted from animals to people).

Some individuals and organizations do promote composting cat or dog waste, and there are even pet waste composters commercially available. However, if composting pet waste, set up a separate system for it (away from all food production gardens and water sources such as wells), and don’t apply the finished product near produce gardens or drinking water sources.

Are black walnut leaves and hulls toxic in compost?

Black walnut leaves, bark, and hulls contain a substance called juglone that is toxic to some plants. However, this toxin can be broken down through exposure to bacteria, water, and air. For black walnut leaves, at least 2-4 weeks of composting is required to get rid of the toxin (or a couple of months sitting in regular soil). Sawdust or chips from black walnut tree prunings and black walnut hulls should be composted for at least 6 months (and preferably longer) to ensure safety, so you may wish to set up a separate system for walnut-related materials. If you’re not sure that the toxin has been eliminated, plant tomato seedlings in the compost to see if they’ll grow.

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