By Jeremy Marin

Concerns about smelly compost usually come from people who, understandably, don’t realize the difference between a compost pile and a pile of garbage.

So what are the differences between a pile of compost and a pile of putrid, foul-smelling, slimy ick? Carbon and air.

Carbon and air in a home compost pile keep the smells down and are necessary to make good compost. Adding carbon (two times as much, by volume) in the form of leaves or newspaper (no glossy or advertising pages, please) give the good microbes something to eat, helping them flourish. These microbes also need air, which is supplied by turning and mixing the pile.

Knowing this, let’s look at your indoor kitchen pail. The only real way to keep this from smelling bad is to empty it often, at least every two or three days. There’s no need to add carbon or air here because you’re going to put it outside before it has a chance to smell bad.

You can buy all the fancy countertop pails with all the filters you want, but that only keeps the smell away if the lid is closed. Once you open that lid, if you’ve left it there too long, you’re going to get a whiff of a garbage pile, not a compost pile. I recommend a small container, which forces you to empty it often. I’ve tried a few, but prefer my stainless steel pail which is attractive, sturdy, machine washable and has a lip that allows me to pour without drips down the side. I leave the lid off for easy additions and empty frequently.

Outside you’ve got to add some carbon and air if you want to keep smells down. For every pail of kitchen waste, add two or three pails of carbon in the form of leaves or newspaper, preferably torn or run through a shredder. Scratch them together a bit with a cultivating fork or pitchfork and pat yourself on the back.

Without the carbon and air, you’ll have a pile of garbage. With them, you’ll have great food for your soil.

Bottom-door style compost units which require only a shovel to aerate, called The Earth Machine, will be available by pre-order only from Arlington DPW, for $40. Contact DPW by May 10, 2015 at 781-316-3108. Cylindrical models which hold more material, called “New Age Composters,” are available daily from DPW for $50. For more information about both these models, visit arlingtonma.gov/recycle.

Jeremy Marin is an Arlington-based compost and gardening enthusiast. A longer version of this piece, as well as more information about composting and energy efficiency, can be found at ArlingtonHEET.org