Your Compost Ingredients
What to Compost

Your compost ingredients come mostly from the garbage side of your life. The recipe for compost success doesn't start out pretty but with a little knowledge you can make a truly remarkable substance for your garden and eliminate up to 60% or more of your garbage.

Here's a preview of what is coming up in the land of compost ingredients.

What to Compost ... Once Living Now ... Yuck ...

For me, and I suspect many of you, my compost ingredients are bits of shameful debris, reminders of life's little failures. Today for example I found a box of cereal that was best before a year and a half ago and four cans of tomato soup that have a date of 2004 stamped onto them. It's November 2011. My son's cold has morphed into an ever increasing mound of used kleenex. My dog absolutely refuses to eat any of the bag of treats I bought for her several months ago.

The back of the fridge has become more a cold storage for compost ingredients than a place to store food fit to eat. It's too late for the wiener and pork chop that somehow escaped my notice. The lettuce is dried up, the cucumber is a liquid slop, and there are endless little containers filled with bits and pieces of leftovers - testament to food failures gone by.

And..... out in the garden dead weeds still stand and my willow trees are finally parting with a few of their leaves.

It is tempting to clear the slate, clean the whole mess up and send it away. To toss the kitchen disasters in the trash, to flush foul liquids down the drain and bag the weeds and leaves for the town to deal with, in short to move the whole issue off my plate and on to the landfill and sewage system.

...But we all know that all this stuff really belongs in our compost, don't we...these are all great compost ingredients.

The Carbon Nitrogen Ratio - A Working Definition

On this planet, all living things, and all things that were once alive, have both carbon and nitrogen as part of their bodies. All of these once living things are potential compost ingredients and are the food for the legions of organisms waiting to turn those materials into the humus rich compost you want for your garden.

When figuring out what to compost it is useful to know the approximate carbon nitrogen ratio of the various compost ingredients. The Carbon Nitrogen Ratio, or C/N ratio, is simply a measure of the proportion of carbon to nitrogen in a particular substance. For example, used coffee grounds have a C/N ratio of about 20, or 20 parts carbon to 1 part 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. Materials with ratios over 30 are considered high carbon and are often called browns for compost.

Nitrogen is the microbes protein. All proteins contain nitrogen and the microbes put together these proteins to allow themselves to grow and reproduce. Materials with a C/N ratio of 30 or less are considered high nitrogen and are often called greens for compost.

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

Using C/N Ratios to Make a Balanced Compost

When I think about what I'm going to compost I find it useful to put the various compost ingredients into one of four different categories:

  • Very High Nitrogen - C/N less than 10 - Hot Greens
  • High Nitrogen - C/N between 10 and 30 - Greens
  • High Carbon - C/N between 30 and 80 - Browns
  • Very High Carbon - C/N over 80 - Dry Browns
You'll find an explanation of these categories below along with examples of materials that fit each group.

The greens tend to be heavier and to collapse in the compost while the browns are dry, lighter and often retain their structure longer in the pile and so maintain air pockets through the material. so you do want to have a mix of both in your compost.

Now, you can do the math. You can take each of your ingredients and calculate the amount of carbon and nitrogen that each will contribute. From that you can then calculate a recipe that will take you close to the ideal compost starting point of a C/N ratio of 25-35.

However, most people, including me, wing it. A decent mix to start is 1 part greens to 1-2 parts browns. This will give you the carbon and nitrogen balance and should help keep the air in the compost.

Common Compost Ingredients and Their C/N Ratios

Following are lists of common compost ingredients and their C/N ratios. I generally recommend composting absolutely everything that can be composted. However, you do need to avoid materials contaminated with one or other of several very persistent herbicides.

Most herbicides and pesticides breakdown easily in the composting process, however, those with residues of picloram, clopyralid or aminopyralid herbicide do not. They remain active even after going through the digestive system of a cow or horse and can remain active enough for a decade or so to affect very sensitive crops such as peas, beans and other legumes.

Those items listed in red are ones you want to check out before adding them to your compost. More details about these persistent herbicides can be found here.

Very High Nitrogen - The Hot Greens A Compost Accelerator

Materials with a C/N ratio under 10 are considered very high in nitrogen. These can also be used as a compost accelerator or activator. Nitrogen tends to heat the compost up and moves bacterial growth and reproduction into high gear. Here are examples of these materials and their approximate C/N ratio.

  • urine - less than 1
  • seed meals - 6-7
  • bone meal - 6
  • blood meal - 3
  • fish wastes - 3
  • dry dog or cat food - 6-10
  • many manures - poultry, pig 6-10
You might want to add one of these materials if your compost doesn't seem to be breaking down.

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 green is not about the color but about the nitrogen level. Many greens, such as coffee grounds for example, are actually brown in color. Most of the material from your kitchen is going to come from this category.

The ratios shown are approximate. Materials in red need to be checked to make sure they are not contaminated with persistent herbicides. 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 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. Materials in red need to be checked to make sure they are not contaminated with persistent herbicides.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:

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

Putting It All Together - Layers or Mixed

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.

For More Information...

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

Leaves - a great source of carbon but can cause problems

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

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.

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