Composting Basics: What Actually Makes It Work

What composting actually is

Composting is decomposition under controlled conditions. You are not making compost. You are creating the right conditions for microbes to make it for you. Bacteria, fungi, and other organisms break down organic material into a stable form that looks and smells like dark, earthy soil.

The output is called finished compost or humus. It adds nutrients to soil, improves water retention, and feeds soil microbes. A handful of finished compost contains billions of beneficial organisms.

The carbon-to-nitrogen ratio

This is the most important variable in composting. Microbes need carbon for energy and nitrogen to build proteins. The ideal ratio is about 25:1 to 30:1 carbon to nitrogen.

In practice, this means mixing browns (high-carbon) with greens (high-nitrogen) in roughly a 3:1 ratio by volume.

How to read your pile

Your compost pile tells you exactly what it needs. Learn to read it.

• Ammonia smell: Too much nitrogen. Add browns. Cardboard or dry leaves work fast.
• No activity, no heat: Too dry, too much carbon, or pile is too small. Add water and green material. Turn the pile.
• Wet and smelly (sulfur, rotten egg): Anaerobic. Pile is too wet and lacks oxygen. Add dry material, turn the pile, and stop covering it tightly.
• Hot in the center only: Pile is too small. Add more material on all sides or build a second pile and combine them.

Moisture: the wrung-out sponge rule

Grab a handful of compost and squeeze it. A few drops of water should fall. That is the right moisture level. No drops means too dry. A stream of water means too wet.

Moisture is easy to fix. Too dry: water the pile when you turn it. Too wet: add dry carbon material (cardboard, straw) and turn to expose wet material to air.

Aeration: why turning matters

Aerobic microbes need oxygen. Without regular turning, the pile becomes anaerobic. Anaerobic decomposition is much slower and produces unpleasant smells.

Turning a pile every 2-3 days produces finished compost in 3-6 weeks. Turning once a week produces compost in 2-3 months. An unturned pile takes 6-12 months.

A tumbler composter makes turning a 10-second task. Read our tumbler composter guide if turning an open pile does not appeal.

Particle size

Smaller pieces decompose faster. A whole cardboard box takes months. Shredded cardboard takes weeks. Chop or shred inputs when possible. For kitchen scraps, smaller pieces break down faster in the pile. Large chunks slow the process.

What not to compost outdoors

Meat, dairy, oily food, and cooked food attract pests in outdoor piles. They also slow decomposition. Standard outdoor bins and piles should stick to fruit scraps, vegetable peels, coffee grounds, eggshells, and dry plant material.

If you want to compost meat and dairy, an electric composter like Lomi handles those inputs without attracting pests.

When compost is finished

Finished compost is dark brown to black, crumbly, and smells earthy. Individual inputs are no longer identifiable. It has cooled down to ambient temperature and holds that temperature through a full pile turn.

If you can identify apple cores and egg shells, it is not done. Give it more time and more turns.

Common questions