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Simple 3-bin compost system

Credit to Milo Martinovich

The following was condensed and adapted based on Milo Martinovich’s “The 3-Bin Compost System – Everything You Need To Know” published on March 29, 2023. Martinovich provides much more detail.

Our community garden already has one 6-bin unit and a separate 3-bin unit. The latter will be used to store amendments. The 6-bin units will now be labelled as two 3-bin units. The following summarizes some content from Martinovich’s very helpful blog. It was also simplified and adapted for a community garden setting.

Benefits of The 3-Bin Compost System

  • Simplest setup
  • Compost in weeks or months
  • Smaller piles mean less weight, less work, easier cycle, easier to stir, easier to manage
  • While regular flipping could help, it is not necessary

Three bins

Bin 1

The minimum size of this pile of bulk compostable material is 3 cubic feet in order for the biomass to get warm enough to kill off pathogens. Even then, this compost system will not kill weeds so we do not add them. This bin will contain the most biomass—fresh garden scraps and waste including plants from pruning, bits of clean cardboard, etc but no weeds or food scraps except for egg shells, banana peels.

Bin 2

Add composted material from Bin 1. In this stage 2 of composting, do not disturb. Some of the composted material will be ready to flip into Bin 3 faster than others. Leave compost that is not fully composted in this bin.

Bin 3

Finished compost ready to be harvested and used. Compost is ready to be harvested when you no longer recognize the material you put into it.

The temperature in centre of the bin may be cooler than the edges. Hot compost can hurt plants; cool compost feeds them.

Finished compost can be placed around but not touching your growing plants.

Greens and browns in Bin 1

An ideal compost pile will have a carbon/nitrogen C:N ratio of c. 30:1 to promote the healthiest composting process. Carbon materials—browns, and nitrogen materials—greens carbon/nitrogen C:N ratio that promotes the healthiest composting process.

We need more carbon or brown materials (30 units) that nitrogen or green (1 unit). This colour category does not always match the materials.

Carbon materials or browns include nutshells, fall leaves, paper, cardboard, straw, shredded branches, coffee filters, dryer lint. We usually have lots of fall leaves! The compost is near a huge cottonwood tree but unfortunately its leaves do not compost rapidly. In the fall, we collect leaves from the Rowan tree for example.

The greens or nitrogen materials include coffee grounds, tea bags, eggshells, prunings, etc from garden plants.

Compost works best when there is a variety of ingredients because that results in a variety of nutrients. Mixing in all of these ingredients together will create a nutrient-rich compost.

Martinovich suggests treating your compost pile like a lasagna with layers of greens and browns.

The first process of decomposition starts in Bin 1. Bacteria and fungi build up from the soil. The compost temperature will slowly increase. After 3-4 weeks the composted material at the bottom of the pile will be read for Bin 2. This composted material will be uniform in colour—a dark rich earthy colour. When you flip the compost pile each time you fill Bin 1, this exposes the compostable material to more oxygen needed for the survival of bacteria and microorganisms that create the compost. Flipping the pile also helps it to heat up. A hotter pile results in compost that can be harvested faster.

Notes

  • We have covers for the bins to keep out animals and to protect from heavy rainfall.
  • The compost facilitators may choose to make adjustments to the size of the bins and may choose to add removable slats in the front of each bin to make it easier to flip using a pitchfork.
  • If we have enough rain you may not need to water often. But if the compost dries too much, you will lose the microorganisms that keeps your compost warmer and makes compost faster. Cold composting takes longer but still makes high-quality compost. Cold composting takes a lot longer to finish.
  • If the composted material have too much water, the environment becomes anaerobic. This gives off a very bad odour, and compost should not have a bad odour.
  • Composting piles needs to be kept as damp as a damp sponge, too wet and it will begin to have an unpleasant odour—too little and the composting process slows down.
  • We capture water from the roof of the tool shed in a rain barrel. One possibility is to use a garden hose system to water the compost.