The Law of Conservation of Energy states that energy is neither created nor destroyed. It is simply transformed. The truth is that all living beings eventually die and decay. Composting capitalizes on the transformative death/decay process to build soil and plant health.
Seven years ago our little farm began with a compost pile (pictured above). Since then, composting has become one of my favorite activities. How much do I like it? Well, I have two compost piles in the shade garden, a compost tumbler and compost bin in our original garden, a compost bin on the front porch, another one in the greenhouse, and four vermicompost bins in the laundry room. In addition to those, I also compost in place in my garden beds during the winter.
So what is compost exactly and why is it so important? Well, different composts are different things. The vermicompost we make is very different from the compost we make outside. I'll explain more about that later but here's what all compost should have in common: it should be alive, and it should have a carbon to nitrogen ratio (C:N) of approximately 20-30:1 in whatever unit of measurement you prefer. It also needs to be completely decayed which means that none of the parent material should be recognizable, and it should have a pleasant odor.
First, let's tackle C:N. All we're talking about is the ratio of brown material to green material. If you look at the above photo you will see brown leaves (carbon) and green grass (nitrogen). You will also notice that there are many more leaves than there is grass. For those of us who are composting other materials such as animal manures, there are charts available online showing the C:N values of those materials. Just type C:N in your search engine of choice and prepare to be overwhelmed by the number of options available!
Now let's address the part about compost being alive. Whether they know it or not, all people who compost are microbe farmers. The compost doesn't just happen by itself. The parent material is transformed into compost by countless microscopic bacteria and fungi. Your role is to provide the conditions necessary to sustain the populations of beneficial microbes.
You can rely upon your sense of smell to determine whether or not you have the right bacteria at work. You are trying to promote aerobic bacterial populations rather than anaerobic populations. Many anaerobic bacteria cause plant diseases. If your compost pile stinks, you have anaerobic bacteria. They normally proliferate when your compost pile is too wet. In that case you need to turn your pile and keep it a little drier. They're called anaerobic because they can't tolerate oxygen. Turning the pile aerates it. Problem solved!
There's one more point that needs to be made about what all composts have in common. They are not fertilizers. They're much more important than that. Compost is actually a way to improve soil structure by adding humates and a method for innoculating the soil by adding beneficial microbes. Humates hold nutrients in the soil for uptake at a later date and you can think of the microbes as a probiotic for your plants. Just as we need beneficial bacteria in our gut to digest our food for us and make nutrients available, plants need beneficial bacteria in their rhizosphere (root zone) to make nutrients available for uptake. Teaming with Microbes by Jeff Lowenfels and Wayne Lewis is an excellent resource for learning more about the soil food web.
There are many different ways to compost, but they all fall into two main categories: cold and hot. Cold composting is generally less labor-intensive than hot composting so it is the method I prefer even though it takes longer to get a finished product. All cold composting means is that it doesn't get to a temperature of 131F (55C) for at least three days. If you want to do hot composting, I suggest that you get a compost thermometer to monitor temperature.
Regardless of whether you want to do hot or cold composting, you need to be aware of moisture levels, temperature, and air. Your temperature is determined by the materials in the pile. Why is the 20-30:1 C:N value so important? Because nitrogen levels determine how fast the pile will heat. That's why you should never put raw chicken manure in a vermicompost bin. The high nitrogen content will cause a catastrophic heating event, killing your worms. If your compost is wetter than a damp sponge, it's too wet. If it's not that wet, it's too dry for microbial life. And we already discussed the need for air when talking about aerobic vs. anaerobic bacteria.
So what makes vermicompost different from other cold composts? Vermicompost is more nutrient-dense and confers resistance to plant pathogens. I use vermicompost for seed-starting and container gardening. When those seedlings are transplanted to garden beds, the nutrients and pathogen resistance goes into the soil with them. I use aerated compost (that's the fancy name for a backyard compost pile) primarily for building soil structure in my various gardens by adding humates in bulk. So there you have it: different composts being used for different things in the garden even though they have similar structure and function.
Worms Eat My Garbage by Mary Appelhof
Compost, Vermicompost, and Compost Tea:Feeding the Soil on the Organic Farm by Grace Gershuny
Teaming with Microbes:The Organic Gardener's Guide to the Soil Food Web by Jeff Lowenfels and Wayne Lewis.