Composting in small spaces: bins, tumblers, worm bins and what to leave out

At a glance

Choosing a system by the space you have

The EPA's home composting guide notes that micro-organisms do the work: they use carbon and nitrogen to grow, water to digest and oxygen to breathe. Any container that holds the right mix and lets air in can work, so the choice comes down to space, neighbors and how much material there is.

Bins and tumblers compared

Tumbler tips

• Size. Oregon State Extension's Linda Brewer finds larger tumblers generally better, and small two-chamber models too small to stay warm in winter unless they are double-walled. Check that the legs and turning mechanism are sturdy.
• Start dry. Begin with bagged leaves from the previous fall, or straw, then add food waste as it is produced; the leaves or straw absorb the liquid, since food waste and grass clippings are mostly water (Oregon State).
• Expect leaks. Tumblers leak dark liquid, especially when food or grass clippings make up much of the load (Oregon State).
• Turn often. UF/IFAS turns the handle a couple of times a week and empties the drum into a wheelbarrow or bucket when the compost is ready.
• Be patient. Brewer calls the process very slow and finishes partly composted material in a turned hot pile.

The mix: browns, greens, water and air

The lists follow the EPA. Arizona's Yavapai County Master Gardener guide gives the target as a carbon-to-nitrogen ratio of 25:1 to 40:1, a chemical ratio rather than a count of buckets. Size matters as much as the mix: Kansas State's minimum for home gardeners is 3 × 3 × 3 feet, because smaller piles may not heat correctly, while oxygen reaches only 18 to 24 inches in from every side, so a pile should not be too large either. Minnesota Extension gives 3 to 5 feet in each direction. A tumbler that fits in a couple of square feet holds far less than that, in line with Oregon State’s note that small two-chamber tumblers do not stay warm in winter unless they are double-walled.

Starting a small bin, step by step

1. Check local rules. Cornell's Steve Reiners advises checking whether your town permits backyard composting; Minnesota Extension says municipalities may set acceptable bin designs and sizes.
2. Pick the spot. Accessible year-round, well drained, not against a fence and near a water source (EPA).
3. Collect scraps indoors. Use a closed container on the counter, under the sink, in the fridge or in the freezer (EPA). Freezing scraps in an airtight container slows rotting and keeps odors and fruit flies out of the kitchen (UF/IFAS).
4. Lay a base. Start with 4–6 inches of bulky browns for drainage and airflow (EPA).
5. Layer and cover. Alternate greens and browns, chopping tough scraps such as corn cobs and broccoli stalks, and cover food scraps with 4–8 inches of dry leaves or other browns (EPA). A few shovelfuls of older compost or garden soil add microbes (Cornell).
6. Keep it moist and turn it. Turn occasionally with a garden fork, moving the outside to the middle. A well-kept pile can reach 130–160°F, which helps reduce pathogens and weed seeds (EPA).
7. Harvest. When the pile stops heating and no scraps are visible, let it cure for at least 4 weeks; it shrinks to about one-third of its original size. Screen it through ¼-inch hardware cloth and return the leftovers to the active pile (EPA). Finished compost is dark and crumbly, smells earthy and no longer heats up after mixing (Cornell Cooperative Extension).

What not to compost in a home bin

Most of the list comes from the EPA, which explains that backyard piles generally do not get hot enough to fully break down animal products, and that commercial facilities may accept items a home bin cannot handle.

Manure is handled differently: Reiners accepts horse, cow and sheep manure and waste from rabbits, hamsters and guinea pigs, while Cornell Cooperative Extension's Q&A says to be careful with manure.

Fixing common problems

Worm bins in brief

Worm composting takes little space and can be done indoors under a sink, in a closet or in a basement (EPA). The EPA's basics: a dark bin with a tight lid, red wigglers (Eisenia fetida) rather than garden or bait-shop worms, about one pound (roughly 1,000 worms) to start, and a temperature of 59–77°F. Cornell Cooperative Extension feeds about ½ pound of scraps per day for each pound of worms, buries scraps under the bedding, and leaves out citrus, meat, dairy, oil and pet waste. Castings are ready to harvest after 3–6 months and need no curing (EPA).

Using the compost

As a soil amendment, the EPA mixes 2–4 inches into the top 6–9 inches of soil; as a mulch, it spreads a 3-inch layer a few inches away from stems and trunks. Cornell Cooperative Extension mixes 1 part vermicompost with 2 parts soil for pots. For filling a raised bed with a topsoil-and-compost blend, the volumes are worked out in the raised bed soil calculator; pot volumes by crop are in container sizes for vegetables.

Where sources differ

Small-space composting checklist

• Local rules checked for backyard bins.
• System matched to the space: worm bin or drop-off indoors, tumbler on a patio, enclosed bin in a small yard.
• Lidded scrap container in the kitchen, or scraps frozen.
• A stock of browns kept dry: leaves, shredded cardboard, non-glossy paper.
• Food scraps always covered with browns.
• Moisture checked: wrung-out sponge.
• No meat, dairy, grease, pet waste or seedy weeds.
• Finished compost cured, screened and used in beds or pots.