What to Compost
Your Compost Ingredients

Your compost ingredients are food for the microbes who will do the actual work of composting.

When you are asking what to compost your answer is anything organic. Here the word organic is used in its scientific sense. Those of you who have studied organic chemistry know that organic refers to the presence of organic carbon.

Your list of compost ingredients which will at least in theory decompose given the right conditions is incredibly broad. It Includes:

• any plant matter - green, brown, dried, made into paper or cardboard, wood chips or sawdust, sea weed etc.
• dried up animal matter including feathers, bone. blood, hoof or horn meal, eggshells, etc.
• manures

Usually compost instructions advise against these compost ingredients: meats, dairy products, oils, weedy plants that have gone to seed, diseased plants, and dog, cat and human poop. All of these could be composted given the right conditions - it's just that the right conditions are not easy for the home composter to provide. If you're interested there are links at the bottom of this page leading to more information on some of these more difficult to compost materials.

As well, for you organic chemists, many petrochemicals, including some herbicides and pesticides, as well as explosives such as TNT can be composted. I don't recommend that you include these in your compost pile, but there is a whole new and very exciting field called bioremediation where compost technology is being used to help clean up contamination by these organic, in the scientific sense, materials.

Like us the compost microbes work best if given a balanced diet. The main compost ingredients from the composter's point of view are carbon and nitrogen.

Carbon is the fuel. It supplies the energy the microbes and other soil biota need to go about their day to day work. It's much like the carbohydrates that we eat.

Nitrogen is the microbes protein. All proteins contain nitrogen and the microbes put together these proteins to allow themselves to grow and reproduce.

Your compost needs other elements in small amounts. The amounts needed are so small that you can trust that any combination of biodegradable material will provide your decomposers with their needs.

Carbon Nitrogen Ratios - What are They and Why are They Important

Composters use a ratio - the Carbon/Nitrogen ratio - to help decide what a good balance of compost ingredients would be. The ratio compares the amount of Carbon to the amount of Nitrogen in any one material. With the exception of urine, there is almost always more carbon than nitrogen in biodegradable compost ingredients.

For example used coffee grounds have a ratio of about 20 parts carbon to 1 part nitrogen. We say it has a C/N ratio of 20. When you put together your compost you aim for a mixture that will give you a C/N ratio of about 25 to 30.

I love exact numbers and those books and web sites that tell me things like the C/N ratio of whatever is 26.3. I get real excited because I have a lot of whatever and now I know so darn much about it. This fails to take into account that my whatever and their whatever were grown in different fields at different times of the years and so - you guessed it - they don't have the same C/N ratio.

We really have to leave exactness to scientists and big municipal composters. They can take samples and make measurements in their labs that give exact values about some material at some moment in time but ... that moment is over for you and me.

Approximate C/N Ratios of Common Compost Ingredients

It is useful to have an idea of approximately where on the continuum of C/N ratios your compost ingredients fit. Then you'll have some ideas of the proportions of various materials you need to make a nicely balanced compost.

In my mind I divide compost ingredients into four categories.

Very High Nitrogen - The Hot Greens or Activators and Accelerators

These have a low C/N ratio - somewhere between 0 and 10. Nitrogen is something that tends to heat the compost up. It moves bacterial growth and reproduction into high gear. The ratios shown are approximate. The materials include:

• urine - less than 1
• seed meals - 6-7
• bone meal - 6
• blood meal - 3
• fish wastes - 3
• Many manures - poultry, pig 6-10

These items work both as a regular part of compost and can be used as activators or compost accelerators.

High Nitrogen - The Moist Greens

These have a C/N ratio of between 10 and 30. They are referred to by many people as greens. The ratios shown are approximate. The materials include:

• food scraps - 15
• coffee grounds - 20
• hay from legumes like alfalfa and clover - 15 - 20
• grass clippings - 15 - 25
• fresh green weeds and plant waste - 25-30
• cow and horse manure - 15-20
• seaweed - 30
• leaves from leguminous trees such as Alder - 20-30

High Carbon - The Dry Browns

These have a C/N ratio of 30 to about 80. These are the drier browns. The materials in this category are important not only to balance your carbon nitrogen ratios, they are also important in providing your compost the structure it needs to maintain some air and oxygen flow through your compost during its decomposition. The ratios shown are approximate. The materials include:

• dried leaves - 35 - 80
• straw - 75
• hay from non legume crops - 50
• corn cobs and stalks - 75

Very High Carbon - The Dry Browns

These have a C/N ration of over 80 and up to as much as 800. These materials can be useful when dealing with a lot of very high nitrogen wastes. For example, if you were composting a lot of fish waste which has a C/N ratio of about 3 you might balance your compost with sawdust which has a ratio of about 300. These materials can also be important for maintaining air pockets in the compost. The ratios shown are approximate. The materials include:

• shredded cardboard - 300 - 500
• paper - 100 - 800
• toilet paper, paper towel and gift wrap rolls - 200-350
• used paper towels, napkins and kleenex - 100-200
• sawdust - 300
• woodchips - 400

Here is a site with a comprehensive list of ingredients for organic fertilizer. These ingredients will also be excellent additions to your compost.

How to Balance the Compost

To balance your compost you combine greens with browns. A rule of thumb is one part greens to one part browns.

If your brown tend toward the very high C/N ratios you might balance them with extra greens or some of the very high nitrogen items.

The Layer Method versus Just Mixing It Up

Most of the diagrams you'll find of compost piles show neat little layers of greens, browns and soil. Layers may make sense if you build your entire pile in one day and if you are sure you will turn the pile a few times during its life.

However, most of us add compost ingredients to our piles in dribs and drabs every few days. As well, many of us never get around to turning our piles. We just feel guilty that we have not done so. Given this real state of affairs in the average compost pile consider mixing your browns and greens together as you add them.

I take my coffee grounds and kitchen scraps and mix them with some shredded bills (a very satisfying end to those bills I might add) and dump them in. It works for me.

Don't worry. If things seem wrong fiddle with your mix. Add more greens if things are slow and more browns if things are stinky. Relax. Nature will prevail in the long run.

Special Considerations for Some Common and Uncommon Compost Ingredients

Grass Clippings - a great source of nitrogen but can cause some problems

Leaves - a great source of carbon but can cause problems

Meat, fish and dairy products - usually not great for home composters but there is a solution

Weeds gone to seed - how to handle this problem.

Diseased Plants - can any of them be composted.

Difficult Plants - Alleopaths - black walnut, sunflower seed shells, eucalyptuses

Pet Poop - some is okay for the compost but some needs special handling

TNT, explosives, petrochemicals etc. - amazingly these materials can be composted, in fact that is one way that toxic sites are being cleaned up. However, don't do this at home.

Materials contaminated with Picloram, Clopyralid or Animopyralid herbicides - Pretty much everything but these herbicides decomposes safely in your compost. If materials contaminated with these pesticides get into your garden you'll be paying for years.