Compost Primer
Operational Path
Part 1: gathering materials
The first step in active compost-making is gathering inputs to build a pile. There are four main principles for selecting compost materials: (1) use a diversity of organic inputs, (2) assess key input characteristics, (3) avoid materials that may disrupt microorganisms and/or contaminate soils, (4) and target a 25:1 - 30:1 ratio of carbon-to-nitrogen (C:N) in the final mix.
A huge range of organic materials can be composted, including many resources from around your yard, neighborhood, and kitchen that are often sent to landfills. If you look online, you’ll find different opinions about what materials are good to use. We’ll share a bit about common organic materials and suggest a few to avoid (at least initially).
Basic inputs
There are simple and tested materials, such as aged wood chips, fallen leaves, dried grass and hay (free of agrochemical residues), used coffee grounds, eggshells, cracked grain, various seed-free plant tissues, vegetable and fruit scraps, and farm-animal manures (free of disruptive compounds like dewormers). These are all typically great, if kept relatively dry until the compost pile is built.
Questionable inputs
Many people also use shredded cardboard and paper, but some manufactured products have non-organic coatings or components; avoid environmental contaminants (heavy metals and ‘forever chemicals’). In general, greasy materials, such as meat, CAN cause issues, and human or pet waste CAN increase biohazard risks. Avoid these inputs or take careful precautions.
The Mix
When assembling a pile, it’s important to utilize diverse materials. For example, old leaves and aged wood chips collected from different trees can make up 50% or more of a pile’s volume. You can achieve a fairly ideal mix of different inputs using careful estimates of each type’s C:N ratio.
Target a 25:1 - 30:1 ratio of C:N in your final mix. That’s an estimate that for every nitrogen atom in the pile, there are around 25 - 30 carbon atoms. Microorganisms tend to thrive in piles near that range, generating heat and breaking down materials.
Estimating C:N ratios and investigating material characteristics can be tricky. While trustworthy sources of information about average ratios is important, direct knowledge about input production and storage is key. For example, more N is often found in plants harvested early in the season (such as early alfalfa) when substantial protein is in aboveground tissues. Hay cut from mature plants often contain relatively less protein (and N). Likewise, if materials get wet during, they can lose N during storage.
Learning to make good estimates about C:N ratios is a key composting skill. This requires a ‘mess around and find out’ (MAFO) mindset: use the best information you have, see what happens, and make changes in the future.
The Journey
We encourage starting, developing your understanding, and tinkering to learn what works best for you. Have fun with the growth process…
Setting up a new compost pile and mixing materials: video link
The compost pile is ready to go: video link