Would-be composters with nearby neighbors often shy away from large, messy compost heaps and elaborate, attention-drawing bins. In-ground compost boxes or bins provide gardeners and homeowners interested in inconspicuous composting with an ideal, small-scale composting option. Wood and cardboard decay quickly when directly exposed to moist earth, but plastic trash cans give you a long-lasting material for your in-ground compost box. Although you won't be able to produce large amounts of finished compost with this in-ground compost box, it converts most food scraps and yard waste into nutrient-rich humus within just a few months, according to Barbara Ellis, co-author of "Soil and Composting."
Find a 30- or 45-gallon plastic garbage can with a secure, heavy-duty lid. Purchase a new, unused garbage can, or check with your friends or local community composting organization to see if they have any available for a small fee. Shun plastic garbage cans that may have contained chemical wastes in the past, as the toxic chemicals may leach from the porous plastic into your compost.
Remove the lid from your garbage can. Invert the can on level ground and brace it with your hand. Cut the bottom from the garbage can with a jigsaw, moving the blade slowly but firmly to make an even cut around the entire circumference of the trash can base.
Carry the compost container and its lid to your composting location. Measure the height of the garbage can and dig a hole in the ground that is equal to 3/4 of the height of the container. For example, if your garbage can measures 36 inches tall, then you'll want your hole to be approximately 27 inches deep. Make sure the diameter of the hole exceeds the diameter of the garbage can by about 2 inches.
Insert the base of the garbage container in the hole in the ground, pushing it down firmly until the bottom circumference of the plastic trash can rests firmly on the base soil. Push loose soil around the edges of the garbage can to help secure it in place in the ground.
Fill the in-ground compost container three-quarters full with alternating 2-inch layers of brown carbon-rich and green nitrogen-rich organic waste. Try to find a good blend of waste materials, so that no single item makes up more than a third of your compost materials. For example, a mix of equal parts of shredded newspaper, dead leaves, grass clippings and potato peels would give you a nice balance of carbon- and nitrogen-dense materials.
Spray your compost materials with water to make them about as wet as a wrung-out sponge. Toss several handfuls of finished compost in your in-ground compost box and place the lid on the top. Tie the lid into place with a piece of sturdy twine if you suspect animal pests may try to enter your compost container.