Compost Recipe & Browns to Add to Your Greens

It works out the right blend of carbon-rich 'browns' and nitrogen-rich 'greens' for a compost pile. You enter how much of each material you have along with its carbon and nitrogen content, and it tells you how many browns to add to your greens to hit a target carbon-to-nitrogen (C:N) ratio, the total size of the mix, and the C:N you actually achieve.

Aim for a starting C:N of roughly 25–30:1. Microbes use carbon for energy and nitrogen to build their bodies, and that range feeds them in balance so the pile heats quickly and breaks down efficiently. As composting finishes, the C:N naturally drops toward 10–15:1 in the mature compost.

Too many browns (a high C:N, say above 40:1) starves the microbes of nitrogen, so the pile barely heats and decomposes very slowly — it can sit for many months almost unchanged. The fix is to add more greens or a nitrogen source to bring the ratio back toward 25–30:1.

Too many greens (a low C:N, below about 20:1) leaves excess nitrogen the microbes can't use, so it escapes as ammonia — the pile turns slimy, smelly and can go anaerobic. Adding browns such as dry leaves, straw, cardboard or sawdust soaks up that nitrogen and stops the smell.

Greens are fresh, moist, nitrogen-rich materials: grass clippings, vegetable scraps, manure, coffee grounds, fresh weeds. Browns are dry, carbon-rich materials: dead leaves, straw, cardboard, paper, sawdust, woodchips. Greens have a low C:N (roughly 10–25:1); browns are high (40:1 up to several hundred:1 for sawdust).

It uses the carbon and nitrogen content of each material to track total carbon and total nitrogen in the mix. It then adds browns until the combined carbon-to-nitrogen ratio reaches your target, and reports the browns needed, the total mix size and the achieved C:N so you can see how close you land.

Yes. Even a perfect C:N won't compost if the pile is too dry or too wet — aim for the dampness of a wrung-out sponge (around 50–60% moisture). Browns also add structure and air gaps; turning the pile keeps oxygen flowing. C:N gets the chemistry right, but moisture and air finish the job.

Yes — enter the carbon and nitrogen percentages for whatever feedstocks you have, whether that's manure and straw, kitchen scraps and cardboard, or grass and leaves. The dry-matter carbon and nitrogen approach is universal, so you can blend any combination and still target a balanced C:N.

They're solid planning figures. Real materials vary in carbon, nitrogen and moisture, and the C:N shifts as the pile breaks down. Use the recipe as a starting blend, then read the pile: if it's slow and cool add greens, if it smells add browns. Composting is about steering, not exact prediction.