Compost is a powerful tool that organic gardeners use to build soil and provide their plants with essential nutrients. Composting is the practice of speeding up natural decay processes. We all know that decomposed organic material like leaves, branches and dropped fruit is nature’s fertilizer. Through compost we seek to mimic nature’s genius in the garden. The basic equation for making your own compost is to combine organic materials with soil microorganisms (the tiny to not-so-tiny critters in the soil), and promote the optimum ratio of carbon to nitrogen to promote the microorganisms’ survival.

Carbon (C) and Nitrogen (N)

Decay-causing microorganisms use carbon as a food source, and they use nitrogen to reproduce. These elements are found in different places throughout nature, and provide some of the most basic building blocks of all life. Carbon and nitrogen are both unlocked for use via several natural processes. In composting, the soil critters do this work. As with all things soil, you want to encourage and support the critters, like actinomycetes, fungi, and bacteria that are busy making magic underground. The same goes in composting. Take care of the critters, and they’ll take care of the rest.

When composting, the optimum carbon to nitrogen ratio (expressed C:N), is 25:1. So in longer terms, you want 25 parts carbon for each part of nitrogen that you introduce to your compost pile. Too much carbon will produce a slow, dry, cold pile. This is because the critters have too much to eat but no nitrogen to reproduce, and so their population drops and their activity is limited. Too much nitrogen leads to a smelly, hot, wet compost pile. This is because the critters use the nitrogen to reproduce, and the excess will cause cyclical spikes in their population. The lack of carbon means little food for the critters’ growing numbers, so die-off happens in short order. The optimum pile, or one in which the carbon sources and the nitrogen sources of material are balanced close to that 25:1 ratio, is not strong smelling, remains moist but not overly wet, and will maintain sufficiently hot internal temperatures.

C:N Ratio

So, how does one achieve the optimum C:N ratio? Layering carbon-rich and nitrogen-rich materials, and choosing materials carefully based on diligent observation of your pile will help greatly. Woody, stalky, dry materials such as leaves and straw are considered carbon-rich. Wet or tender materials, like kitchen scraps, manure, and grass clippings are considered nitrogen-rich. Most gardeners find that nitrogen is easier to supply, and have to think carefully, or do some sourcing, to find proper carbon-rich additions.

The most basic compost pile includes leaves, grass clippings, soil, and some water. Layering these materials, ensuring they remain evenly moist, and turning the pile with a pitchfork every few days will produce usable compost fairly quickly. As you get familiar with your pile, you’ll know which materials to supplement to affect the pile’s overall health. Below are some common compost materials that you can play with to master your C:N ratio:


  • Choose an out-of-the-way site for your compost pile, not too close to a creek or stream (compost leachate, the moisture that leaks out of your pile, can be ammonia rich, and if it runs into waterways, it will overload aquatic ecosystems)
  • You can build an enclosure for your pile out of old wooden palettes, chicken wire, or other materials. This will contain the pile, and keep hungry raccoons dogs, or other compost thieves out of your compost.
  • Seaweed can help activate your pile. Spray treatments or additions of actual seaweed are ways to incorporate it into your compost.
  • Be sure to include both shredded and whole materials in your pile, to promote aeration for the critters.
  • Turning can happen every couple days to every several weeks depending on your schedule. Know that the more you turn, the faster you’re encouraging the decomposition process to happen.
  • Your compost is done when all materials are uniformly dark and crumbly, and it smells earthy and fresh.
  • Spread your compost using a pitchfork or rake, or your hands! Even if you don’t have much, a dime’s thickness over top of the garden bed does wonders for your soil and your plants.
  • Vermicompost or worm compost is worm castings, and it is amazing for your garden! Vermicompost is teeming with soil critters and is packed with essential nutrients that plants love. You can create your own worm compost very easily. Click here for a vermicomposting tutorial by Ruth Gonzalez.