Fourth Grade NGSS
Biogeology and Heat Generation

Compost Party (Greens and Browns)


  • Making mixture of greens and browns.
  • Scheduling a "Compost Party"


  • proportion
  • compost
  • greens
  • browns


  • food waste
  • coffee containers (to measure out proportion)
  • manue
  • wood chips
  • flyer to go home
  • food waste


All living organisms have a Carbon to Nitrogen (C:N) ratio for their tissues.  For microorganisms, carbon is the basic building block of life and is a source of energy, but nitrogen is also necessary for such things as proteins, genetic material, and cell structure.

Decomposition of organic materials in your compost pile is greatly increased when you create the proper balance between the carbonaceous materials (called BROWN because they are dry) and the nitrogen-rich materials (called GREEN because they are more fresh and moist). This balance is referred to as the Carbon-Nitrogen ratio, and shown as C:N.

Microorganisms that digest compost need about 30 parts of carbon for every part of nitrogen they consume. That's a balanced diet for them. If there's too much nitrogen, the microorganisms can't use it all and the excess is lost in the form of smelly ammonia gas. Nitrogen loss due to excess nitrogen in the pile (a low C:N ratio) can be over 60%. At a C:N ratio of 30 or 35 to 1, only one half of one percent of the nitrogen will be lost. That's why you don't want too much nitrogen (fresh manure, for example) in your compost: the nitrogen will be lost in the air in the form of ammonia gas, and nitrogen is too valuable for plants to allow it to escape into the atmosphere.

  1. A maximum of 35% of the carbon in fresh organic material will be converted into soil humus IF there is sufficient nitrogen present.
  2. A minimum of 65% of the carbon in fresh organic material will be given off to the atmosphere as carbon dioxide due to microbial respiration.
  3. The humus formed from the decomposition of fresh organic material will contain approximately 50% carbon and 5% nitrogen. In other words, the C:N ratio of the humus is 10:1.
  4. Most fresh plant material contains 40% carbon. The C:N ratio varies because of differences in nitrogen content, not carbon content. (Note: Dry materials are generally in the range of 40 to 50 percent carbon, and sloppy, wet materials are generally 10 to 20 percent carbon. Therefore, the most important factor in estimating the carbon-to-nitrogen ratio of plant or food waste is how much water is present).

5.    Generally speaking, you can get C:N ratios of 30:1 to 50:1 by adding two parts of a GREEN material to one part of a BROWN material to your bin. A "part" can be defined as a certain quantity of the material, such as two 5-gallon buckets of GREEN and 1 packed bucket of BROWN.

6.    Play with the chart below. For example, food scraps, grass clippings and leaves come close to an average of 30:1. How? Add-up the Carbon side of the ratio for all three materials, i.e. 15, 17, 60, and divide by the number of materials, i.e. three. 92/3 = about 31:1.

GREEN (Nitrogen)

BROWN (Carbon)

Aged Chicken Manure    7:1
Fresh manures are way to hot and can burn your plants and roots!

Leaves   60-80:1
One of the most important ingredients for composting, especially shredded or broken down (leaf mulch).

Food Scraps   17:1
Vegetable Scraps   25:1

Straw, Hay   90:1
The best way to use is to shred for faster breakdown.

Coffee Grounds   25:1

Sawdust   500:1
Commercially produced compost is high in sawdust or shredded bark chips. Use very sparingly!

Grass Clippings - Fresh   17:1
Dry clippings would be higher in Carbon. Therefore, use as carbon source if necessary.

Woody chips & twigs   700:1
Be sparing. Best use is small material at bottom of bin or pile.

Fresh Weeds   20:1
Make sure you don't compost weeds with seeds, unless you insure that your pile gets hot - over 140F/60C.

Shredded Newspaper   175:1
Has no nutrient content. Best used in vermicomposting. Always shred and soak in water for fast breakdown.

Fruit Wastes   25-40:1

Nut shells   35:1

Rotted Manure   20:1
maycontain undigested seeds that can sprout

Pine Needles   80:1
Use sparingly. Very acidic, waxy; breaks down slowly.

Humus (soil)   10:1
This is nature's natural ratio. Use sparingly in pile. Best used to "seal" the pile by putting a 1-2 inch layer on top.

Corn Stalks   60:1
Shred or cut up in small pieces for fast break down.

Seaweed   19:1
General Garden Waste   30:1

Peat Moss   58:1
Has no nutrient value, mostly filler.



1.  Above information is just for teachers who want to understand more the complex nature of making good compost.  Remember compost is just one component to make enriched soil.  Soil is rocks plus organic matter.  Compost is organic matter.

2.  Schedule a compost party.  Send parents a notice of what you are doing (flyer).  This helps increase their awareness of what experiment their students will be participating. 

Types of food waste needed:          
:  rotten or old lettuce, vegetables (raw or cooked), onion peels or other vegetable parts that were to be thrown away
Fruit:  peels or cores (example, banana peels, apple cores).  Whole fruit is ok but should be cut into smaller pieces. 
:  egg shells, bread (parts of sandwich without meat)

Do NOT  BRING:  (we cannot use these for this specific experiment)

    Do not bring MILK Products (cheese, yogurt, etc)
   Do not bring  Meat (chicken, fish, beef, etc) (egg shells are ok but no eggs themselves
Do not bring  garden clippings




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