Composting for Beginners: The Ratio That Makes It Work

Composting is a managed decomposition process, not a pile of rubbish left to rot. Microorganisms need a rough balance of carbon and nitrogen, enough moisture to stay active, and enough air to avoid turning anaerobic — which is where the smell comes from.

Browns and greens, roughly by volume

A working ratio by volume is roughly two to three parts browns to one part greens. Too many greens produces a wet, smelly, slimy heap. Too many browns produces a dry heap that barely warms up and takes a year or more to finish.

Moisture: like a wrung-out sponge

Grab a handful from the middle of the heap. It should hold together and feel damp without dripping. Bone dry heaps stall completely; soggy heaps go anaerobic and smell of ammonia or rot. Adjust with water or with dry browns as needed.

Air: turn it or build it in

Turning a heap every one to two weeks reintroduces oxygen and speeds decomposition dramatically — the difference between finished compost in 6-8 weeks versus 6-12 months. A heap that is never turned still composts, just slowly, and is the lower-effort choice for anyone who does not need the compost quickly.

• Hot composting: frequent turning, careful ratios, finished in 6-8 weeks, kills most weed seeds.
• Cold composting: little or no turning, whatever is available goes in, finished in 6-12 months, some weed seeds survive.

Worked example: building a balanced load

For a week of kitchen scraps totalling roughly 1 cubic foot of greens, layer in about 2 to 3 cubic feet of browns — a full paper grocery bag of dry leaves or shredded cardboard is a reasonable rough measure. A heap that stalls with a sour, wet smell almost always needs another bag of browns mixed through, not left as a dry top layer, before it will restart heating.

Getting started, step by step

1. Choose a bin or open heap in a spot with partial shade and easy access, at least 3 feet on each side for turning room.
2. Lay a coarse base layer of twigs or straw a few inches deep to help drainage and airflow from the bottom.
3. Add alternating layers of browns and greens, roughly two to three parts browns to one part greens by volume.
4. Water lightly as you build if the materials are dry, aiming for the dampness of a wrung-out sponge throughout.
5. Turn every one to two weeks for hot composting, checking the centre feels warm to the touch after a few days.
6. Stop adding fresh material a few weeks before you need finished compost, and let the heap cure undisturbed.

• Common mistake: adding only kitchen scraps with no dry browns, producing a slimy, smelly heap that never heats up.
• Common mistake: chopping nothing, since whole cabbage stalks or branches take vastly longer to break down than chopped or shredded material.
• Common mistake: letting the heap dry out completely in summer and assuming it has simply finished, when it has actually stalled.
• Common mistake: composting pet waste from cats or dogs, which can carry pathogens that home composting temperatures do not reliably kill.

Using the finished compost

Finished compost works as a soil amendment mixed into beds before planting, a top-dressing mulch layer around established plants, or a lightweight ingredient in potting mixes at roughly one part compost to two or three parts other media. Avoid using unfinished compost directly around seedlings, since the ongoing decomposition can temporarily tie up nitrogen that young plants need.

Bin costs and when a bin beats an open pile

A tumbler is worth the extra cost mainly for people who find turning a heap with a garden fork physically difficult, since the crank mechanism does the same aeration job with far less effort — it does not compost any faster per pound of material than a well-turned open pile of the same volume.