Q: While researching composting, I’ve read that microbial activity is greatest when the carbon-to-nitrogen ratio is 30:1. How can I achieve that using only grass clippings and leaves? Are tea and coffee grounds and eggshells considered to be nitrogen or carbon?
A: It’s true that the 30:1 ratio is optimum for decomposition but Nature rarely reads research. No matter what ratio you use, Nature will find a way to break it down into something useful. Rather than consulting charts of the carbon and nitrogen content of various materials, I’d rather you mix brown landscape debris with green landscape waste in whatever proportion you have. Throw in a couple of handfuls of composted manure and the soil organisms will take over from there.
My rule of thumb is to start taking compost from a pile when you can barely tell what the original components were. In other words, when you can no longer distinguish plant stems, banana peels and individual tree leaves in the mix. Remember that you need a lot of compost to make a difference in your soil: typically one to three inches of organic material spread on a bed and mixed ten inches deep.