But first, a few words about the amount of brown (carbon) material, versus green (nitrogen) material to put into your compost bin. Adding too much brown material will result in a pile that takes a long time to break down wheras too much green material will result in a slimy, smelly pile that doesn’t heat up effectively. In order for our pile to break down quickly and efficiently we need to provide just the right balance of brown and green materials.
The microorganisms in our compost bins need both carbon and nitrogen to thrive; carbon for energy and nitrogen for protein synthesis. For every one unit of nitrogen used by the bacteria they also consume about 30 units of carbon. And so in order to keep the bacteria working efficiently we need to create an environment for them that is approximately 30 parts carbon to 1 part nitrogen.
Unfortunately, most composting materials don’t have a carbon to nitrogen (C:N) ratio of 30:1. However, if we know the approximate C:N ratio of the materials we use in our compost, we can combine them so that the total mixture will be as near as possible to 30:1. This may sound a bit complicated but it really isn’t.
Here’s an example:
We want to have a ratio of 30:1 in our compost bin but we only have access to the following ingredients:
- dry autumn leaves (C:N of about 50:1)
- kitchen scraps (vegetable & fruit peelings, coffee grounds etc: about 12:1)
- grass clippings (about 20-30:1)
- sawdust (fresh: 500:1, rotted 200:1)
Using different combinations of materials we will try to get close to the magic 30:1 ratio. If we use 1 part dry leaves to 1 part kitchen scraps we would have the following:
- leaves 50/1 + kitchen scraps 12/1 = 62/2 = 31/1 or 31:1
If we use 1 part leaves, 1 part kitchen scraps and 1 part grass clippings we would have:
- 50/1 + 12/1 + 20/1 =82/3 = 27:1. Not too bad. In this example we can add some extra leaves or a handful or two of sawdust to bump up the ratio nearer to 30:1
Making the Compost Pile
Start with a 4 inch layer of brush, twigs, hay or straw at the bottom of the compost bin. If you don’t have these materials, dry leaves will do. This first layer should be as coarse as possible to allow air to be drawn up into the pile from the bottom of the bin.
Then add a 4 inch layer of brown material, then a thin covering of finished compost or good garden soil. That’s one layer. The addition of compost or soil is to provide the necessary bacteria to get the compost to start breaking down. If we don’t add this layer the compost will still work, the addition just helps to speed things along.
Then add a 4 inch layer of green material topped with a thin layer of an activator. Activators are a source of both nitrogen and protein, ingredients that assist the organisms to break down the material. There are a number of good activators. Alfalfa meal works amazingly well. You can also use fresh manure, bone meal, blood meal, cottonseed meal, or even high-protein dry dog food (yes, that’s right, dog food!).
Continue adding materials in alternating layers of greens and browns until the compost bin is full.