It has to do with keeping a well-regulated carbon/nitrogen balance. If a compost heap leans too far to the nitrogen side, the extra nitrogen will actually convert to ammonia gas (making it smell gross). A heap that's got too much carbon won't decompose as quickly (obviously one of our open-air problems, along with not keeping our open-air heap wet enough).
According to Organic Gardening magazine, the ideal compost heap has a 30:1 carbon/nitrogen ratio, more easily digest as two parts "browns" to one part "greens" (we know that's more like 2:1 but stick with us). Which is helpful, but... what's carbon and what's nitrogen?
Here are a few easy tips to keep your carbon/nitrogen ratio just right.
Nitrogen (think green): table scraps (non-dairy and non-meat), fruit and vegetable scraps, coffee grounds, tea leaves, grass trimmings, various other green clippings (i.e., weeds, flowers, and seaweed).
Carbon (think brown): dried leaves, cardboard, wood chips, straw, corn cobs, sawdust, dryer lint.
Remember, your compost should always be slightly wet—about as damp as a wrung-out sponge, is what most gardening sources tell us.
Have any other good composting tips? Do share!