Composting is nature at its most efficient: organic waste decays, disintegrates, decomposes, providing food for beneficial microorganisms and insects, eventually releasing nutrients into the soil from whence it all came, allowing the process of growth to continue in a never-ending cycle of life. We gardeners can help the cycle along with careful management of the composting process – and one of the easiest ways is to compost food scraps from your kitchen.
In this primer, we’ll give you an overview of three common, no-brainer methods of kitchen scrap composting: the Worm Bin, the Digester, and The Hole in the Ground.
First of all, what are compostable kitchen scraps? Pretty simple: raw vegetables (or cooked veggies if they’re plain), most fruits, egg shells, used tea leaves and coffee grounds, and uncoated paper stuff like coffee filters and tea bags. Don’t allow animal products – meat, fish, or dairy – or oily foods into your kitchen compost. Animal products attract nuisance pests like flies and rodents, and can stink up the place, and both animal products and oily foods take longer to decompose. Be stingy in adding citrus or any acidic foods as well, as these can be extremely unattractive to worms (“The burn! It hurts!”) and other beneficial organisms .
Won’t my saved scraps make my kitchen stink? Well, y’know, if you’re going to leave your scraps sitting around the house for a week, then, yeah, they’ll probably start to smell because by then decomposition is under way. You’ll also start to get annoying little gnats. A scrap bin with a tight-fitting lid and air holes will help alleviate this (there are plenty commercial varieties out there that can fit on your countertop or under your sink). You can also freeze saved scraps.
So how hard is it? The three methods here are easy to start and easy to maintain. Which one you choose really depends on what suits you best and fits your lifestyle.
Worms are the heroes of food scrap composting: They make quick work of food waste, and their castings (poop) makes for some of the best soil amendment around. A well-maintained worm bin can keep you rich in compost for many, many months. You can build a wooden worm bin for about $50, or make a simple version with off-the-shelf stuff, like this one from Seattle Tilth. A good bin should generally be at least 12″ deep, have a tight-fitting lid, screened ventilation holes on top, and drainage holes on the bottom.
You’ll need moist bedding material (such as torn up newspapers or cardboard, coarse sawdust or leaves), your food scraps, and a starter batch of red worms; you can find these at bait shops, online suppliers, or ask a friend with an active bin. (Remember: Red worms. Not earthworms. Earthworms like mineral soil, red worms like organic muck — which is what you’re putting in the bin.) Simply bury your scraps in the bedding with the worms, every once in a while burying in a new spot; be careful not to “stir” the bedding, though, since this can overheat your worms. Add fresh bedding as it decomposes. Harvest compost when it’s brown and crumbly, and harvest frequently as too many castings can be toxic to your worms. Your worm bin can be kept either indoors or outdoors, in a cool, protected spot. Keep the ventilation and drainage holes clear, and the bedding moist but not wet. Check out this handy five-step guide.
A food scrap digester is a simple container with holes punched in the lower half, buried deep enough in the ground to cover the holes, and covered with a tight lid. With digesters, all you need are your food scraps; since it’s buried in soil, regular ol’ earthworms will do the trick here.
Using a galvanized metal trash can, punch or dill 40-50 holes in the bottom and sides up to 1/3 of the way up. In your garden, dig a pit deep enough to bury the bottom half of the can so that no holes are exposed. Push the soil up against the sides and tamp it down. That’s it! Worms will find their way to the food scraps through those holes and get to work.
Your compost will be ready to harvest in 6-12 months. You’ll need to temporarily remove the top layer of composting material — the newer stuff — to get to the rich compost beneath. For this reason, you can also install two digesters; when the first is full, leave it to finish composting and start a new batch in the second digester, and rotate between the two.
If you do start to notice flies or smells, try adding a thin layer of newspaper, dry leaves or straw on top of each new addition of scraps.
There are also a variety of ready-made digesters on the retail market available to the home gardener.
Hole in the Ground. (No, seriously.)
Listen, some of us are too lazy — er, busy to make things or punch holes. Pit or trench composting is safe and easy, with the added benefit that harvesting the compost is not necessary: once decomposition is complete, you can plant directly over the composted area. (You can also adapt this method to compost in raised beds.)
This method relies on anaerobic (i.e., oxygen-deprived) digestion — the same process that occurs in bogs and marshes. Because it relies on natural decomposition with little interference from us, it may take longer than other methods; therefore, you’ll need to chop up your scraps a bit to speed up the process.
Choose an empty plot in your garden, or an area just outside the dripline of trees or shrubs. Dig a hole at least 12″ deep, and up to 3 feet in diameter, depending on how much food scrap you think you’ll be adding over time. Clear out any roots, rocks and debris. Add your chopped up food scraps to the hole, spread evenly, and cover with a layer of soil. (You can chop the scraps with your shovel as you work.) If you plan to add more scraps later, cover the hole to keep pests and rodents away; a simple wooden board will do. Whatever the area of of your compost pit, make sure to leave room for 6-8 inches of soil at the top to discourage pests and keep the smell at bay, and pack down that final layer of soil. When the pit is full you can cover it with sod, or a wooden board or plastic tarp. Don’t let the area dry out, since those oxygen-hating microorganisms still need water to get the job done.
Trench composting is simply that — a long trench rather than a single hole in which to bury scraps. The trench will eventually become a planting row. You can map out several parallel trenches, composting and then planting them in rotation.
Pit or trench composting can take up to 12 months to complete decomposition, depending on how much material you’ve added and the number of microorganisms in your soil. Check its progress from time to time by turning a little section. Moist and crumbly? Ready to plant!
No matter which method you choose, remember: Composting food scraps is an important component of “closed loop” recycling. It reduces waste, prevents erosion and runoff, improves the soil, and makes your garden grow!