Note: A shorter, slightly different, version of this appeared in the Arlington Advocate.

Concerns about smelly compost usually come from people who, understandably, don’t understand 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.

Steel pails are light, sturdy, machine washable and don’t drip. Ditch the top – it only gets in the way. Image from Gardeners.com for demonstration purposes only – I don’t get any kickback.

You can buy all the fancy counter top 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 dripping down the side. I leave the lid off for easy additions and empty frequently.

Outside you’ve got to add some carbon and air to your pile or it will stink. 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, but not necessary. (Do not put full sheets of newspaper into your pile. At least rip it into strips.) Scratch them together a bit with a cultivating fork or pitchfork and pat yourself on the back.

Things don’t always turn out the way we want.

Does this mean your compost will never smell bad? Do your souffles always turn out perfect? The answer to both is probably “no.” At some point you will dig into your pile and find a section that smells bad. At some point you’ll forget to add carbon, or forget to turn the pile for a month, or discover that you never actually turned that corner of the pile, and now it stinks. (Edit: At some point someone in the family will add a container of expired milk, a hot dog, a block of moldy cheese or some chicken nuggets, and now it stinks.) These things will happen. 

However, If you generally follow the rules (2x as much carbon and aerate occasionally) then the smell will be limited and, after correcting with more carbon and/or more air and mixing, the odor will be gone in a day or two.

Without 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 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.