Carbon and Nitrogen

One of the most important factors to composting is knowing about the Carbon-to-Nitrogen Ratio (C:N). All organic matter is made up of substantial amounts of Carbon (C) and Nitrogen (N). Carbon is needed in your compost pile for the composting organisms for energy and Nitrogen is required for protein production.

Scientists have determined that the C:N should be roughly 25-30:1 for an effective and quick compost. A compost with this ratio will be sweet-smelling, fertile, and fast-acting. Generally speaking, Browns are high in Carbon and Greens are high in Nitrogen.

When adding kitchen waste greens, it is a good idea to also add the correct ratio of browns as well, if you are working with a well established compost heap. Because my compost had consisted mostly of Carbon-rich Browns for so long and had basically "died", I can focus a bit more on adding Nitrogen-rich Greens without adding extra Browns.

You can keep a pile of lawn rakings (leaves and cut grass) in a pile or contained in a fence/bin etc. next to your compost bin, to always have an easy supply of browns when you need it!

Estimated Carbon-to-Nitrogen Ratios
Browns = High Carbon	C:N
Ashes, wood	25:1
Cardboard, shredded	350:1
Corn stalks	75:1
Fruit waste	35:1
Leaves	60:1
Newspaper, shredded	175:1
Peanut shells	35:1
Pine needles	80:1
Sawdust	325:1
Straw	75:1
Wood chips	400:1
Greens = High Nitrogen	C:N
Alfalfa	12:1
Clover	23:1
Coffee grounds	20:1
Food waste	20:1
Garden waste	30:1
Grass clippings	20:1
Hay	25:1
Manures	15:1
Seaweed	19:1
Vegetable scraps	25:1
Weeds	30:1

source: http://www.composting101.com/c-n-ratio.html