Composting Mistakes and How to Fix Them

Why Composting Sometimes Goes Wrong

Composting is fundamentally simple — organic matter breaks down into rich humus, which feeds your garden. But there are a handful of common mistakes that result in slow, smelly, or simply ineffective compost piles. Understanding why these problems occur makes them easy to fix.

Problem 1: The Pile Smells Terrible

A foul-smelling compost pile almost always means one of two things: too many nitrogen-rich (green) materials without enough carbon-rich (brown) materials, or the pile is too wet and has become anaerobic. The fix is the same for both: add generous quantities of dry brown material — straw, torn cardboard, dry leaves, or wood chips — and turn the pile to incorporate them and reintroduce oxygen. The smell should dissipate within a few days.

Problem 2: The Pile Is Not Heating Up

A cold pile that does not generate heat is typically too small (under 1 cubic metre), too dry, or has too little nitrogen to fuel microbial activity. Check moisture — the pile should be as damp as a wrung-out sponge. Add nitrogen sources: fresh grass clippings, vegetable scraps, coffee grounds, or a small amount of blood and bone. Turn the pile to aerate it. If it is too small, add more material and build it to at least 1 cubic metre all at once.

Problem 3: The Pile Is Slimy and Matted

Grass clippings, wet leaves, and fresh kitchen scraps tend to compact into airless, slimy layers that slow decomposition significantly. Break up compacted layers when you add material. Mix grass clippings with dry, structural materials like straw or torn cardboard before adding to the pile. Never add thick layers of a single material.

Problem 4: Taking Forever to Break Down

Slow decomposition is usually caused by materials that are too large, too dry, too cold, or without enough nitrogen. Chop or shred materials before adding to the pile — smaller pieces have more surface area for microorganisms to work on. Cutting your kitchen scraps into smaller pieces, running the lawn mower over dry leaves, and shredding cardboard all significantly accelerate decomposition.

Problem 5: Pests in the Pile

Rats, mice, and other pests are attracted to compost piles that contain food scraps, particularly cooked food, meat, or dairy. Exclude these materials from the pile entirely and use a compost bin with a solid base and lid instead of an open pile. Bury fresh food scraps in the centre of the pile rather than leaving them on the surface.

Problem 6: Compost Full of Weed Seeds

Weeds that have gone to seed should never go into a cold compost pile. The seeds survive and then you spread them throughout the garden when you apply the compost. Either hot-compost these materials (temperatures above 55°C kill weed seeds) or dispose of seeding weeds in your council green waste bin instead.