Compost Browns to Greens Ratio: How Much of Each to Add

The Compost Browns to Greens Ratio

Use two to three parts browns to one part greens, measured by volume. That is the ratio the US Environmental Protection Agency gives for home piles: add at least two to three times the volume of browns, such as dry leaves, to the volume of greens, such as food scraps. In practice, every bucket of kitchen scraps or fresh clippings gets two or three buckets of dry material on top.

Browns are the dry, carbon-rich ingredients. Greens are the moist, nitrogen-rich ones. The microbes that do the composting need both, and the volume rule is a bucket-friendly way of landing near the balance they work best at. You do not have to weigh anything, and the ratio is a starting point that you adjust by how the pile smells and heats.

Browns to Greens Is Not the Same as Carbon to Nitrogen

Two different ratios get quoted for compost, and they are easy to mix up. Cornell’s composting program puts the ideal carbon to nitrogen ratio at around 30 to 1, meaning 30 parts carbon for each part nitrogen by weight. That figure describes the chemistry of the whole blend. It does not mean 30 buckets of leaves for each bucket of scraps.

Every ingredient already contains both elements. Grass clippings sit at about 19 to 1 and tree leaves at 40 to 80 to 1, so a mix of the two lands somewhere between. The 2 or 3 to 1 volume rule exists because dry browns are light and fluffy while greens are dense and wet, and it takes several buckets of leaves to supply enough carbon for one bucket of scraps.

Cornell describes what happens on either side of the target. Below 30 to 1, nitrogen is in excess and is lost as ammonia gas, which is the sharp smell of a pile with too many greens. Above it, the microbes run short of nitrogen, the pile stays relatively cool, and breakdown is slow. As composting proceeds, the ratio falls from 30 to 1 toward 10 to 15 to 1 in the finished product.

Carbon to Nitrogen Numbers for Common Materials

The values below come from Cornell’s fact sheet on composting ingredients. Anything under 30 behaves as a green, and anything above it behaves as a brown.

Material	Carbon to nitrogen	Acts as
Food scraps	15 to 1	Green
Grass clippings	19 to 1	Green
Cow manure	20 to 1	Green
Horse manure	25 to 1	Green
Leaves	40 to 80 to 1	Brown
Bark	100 to 130 to 1	Brown
Paper	170 to 1	Brown
Wood and sawdust	300 to 700 to 1	Brown

The spread among browns is wide. Sawdust at 300 to 700 to 1 has a ratio several times that of leaves, so a pile built on wood shavings needs more greens than one built on leaves, or it will sit cold. Use woody material in small amounts and let leaves do most of the work.

For a yard-waste pile, Cornell offers a simple recipe: one part grass clippings to three parts leaves.

What Counts as a Brown

Browns are dry and usually tan or gray. Besides carbon they give the pile structure, and the air gaps between stiff pieces let oxygen reach the middle. The EPA’s list of browns for home composting includes:

• Dry leaves
• Plant stalks and twigs
• Shredded paper that is not glossy
• Shredded brown bags
• Shredded cardboard with no wax coating, tape or glue
• Untreated wood chips

Fall is the time to stockpile. A few bags of dry leaves kept beside the bin will cover kitchen scraps through the following summer, when greens arrive faster than dry material does. Leave glossy paper and dryer lint out; the EPA lists both among materials to avoid in a home pile.

What Counts as a Green

Greens are fresh and moist. They supply the nitrogen that microbes need to multiply, and that rapid growth is what heats a pile toward the 131 to 160°F range of active composting. The EPA’s list of greens includes:

• Fruit and vegetable scraps
• Grass clippings
• Coffee grounds and paper filters
• Paper tea bags without staples
• Crushed eggshells

Fresh green trimmings from the garden and manure from cows or horses fall on the green side as well, as the table shows. Keep meat, fish, bones, dairy, fats and oils, cooked food, pet waste and diseased plants out of a backyard pile. Weeds need extra care, and there is a separate guide to composting weeds without spreading them.

How to Layer Browns and Greens

The EPA’s building order turns the ratio into something you can see. Start with a 4 to 6 inch layer of bulky browns such as twigs and wood chips, which lets air in at the base and soaks up liquid. Then alternate greens and browns, keeping two to three parts browns to each part greens by volume. Finish every addition of food scraps with 4 to 8 inches of dry leaves or other browns so that no scraps show.

Size and moisture decide whether a well-balanced pile heats. University of Georgia Extension gives a minimum of 27 cubic feet, which is 3 feet wide, 3 feet deep and 3 feet tall, and a moisture content of 40 to 60 percent by weight. The EPA’s field test for that is the feel of a wrung-out sponge. Turning about once a week keeps oxygen moving through the mix. Managed this way, a pile can finish in three to five months, and a neglected one can take a year. If a faster turnaround matters, compare hot and cold composting.

Fix a Pile When the Ratio Is Off

The pile reports its own balance through smell and temperature. Each symptom points to one correction.

Symptom	Likely cause	Fix
Sharp ammonia smell	Too many greens, ratio under 30 to 1	Mix in dry browns and turn
Rotten odor, soggy texture	Too wet, too little air	Add dry browns and turn
Pile stays cool, nothing changes	Too many browns or too dry	Mix in greens, add water, turn
Grass clippings matted into a slab	Greens added in a thick layer	Break up, blend with 3 parts leaves

A compost thermometer takes the guesswork out of the cool-pile case; the guide to choosing one covers what the readings mean. For odors that persist after rebalancing, see why a compost pile smells bad. When the material is dark, crumbly and no longer heats after turning, it is ready, and the next question is how much compost to add to a bed.

Quick recap

• Two to three parts browns to one part greens by volume
• The 30 to 1 figure is carbon to nitrogen by weight, a different measure
• Greens sit under 30 to 1 (food scraps 15, grass 19); browns sit over it (leaves 40 to 80, sawdust 300 to 700)
• Start with 4 to 6 inches of bulky browns and cover scraps with 4 to 8 inches of leaves
• Ammonia smell means add browns; a cool pile means add greens and water