A Short Course on how to make compost, and why

"Composting" is a man-made process that uses nature's own biological processes to reduce large amount of organic material to a small amount of usable "compost", the result of the process. The resulting compost continues to decompose until we are eventually left with "humus", the end result of decomposition.

Making compost requires just four things, carbon, nitrogen, air and water. Carbon is supplied by 'brown' materials (dried leaves, dried grass, straw, woody plant trimmings, shredded paper),while nitrogen is supplied by 'green' materials (fresh grass trimmings, fresh kitchen waste, wilted weeds, etc.). Water is required by the decomposition chemistry, and air is required by the micro-organisms that do all the work.

While compost is relatively low in nutrients, what is available is released slowly, making compost a long-lasting fertilizer and soil conditioner. The compost not only yields its nutrients to your plants, it also feeds the living organisms in your soils that help, or are sometimes required, for healthy plants.

Compost may be made simply by making a pile of yard and kitchen waste. It will decompose slowly, and in a year's time give you usable compost. This is easy, but slow, and may not have any effect on weeds or disease organisms in the materials.

Rapid compost takes a bit more work, but has the advantages of generating high heat levels within the pile that kill many weed seed and most disease organisms. Some weed and disease species may not be killed, but most are.

The other advantages of rapid composting are that large amounts of compost may be made throughout the gardening season in as little as 2 to 3 weeks, and you get exercise turning the pile. Contrary to popular belief, a well tended compost pile does not stink (that is a sign that you are out of balance somewhere), but rather has a pleasant, earthy smell.

So, the question is - how do we make a balanced compost pile?

Brown to green ratio - In the compost pile, the carbo to nitrogen ratio should be 30:1. Because the bulk and moisture content of brown and green materials, we can simply use equal volumes of each and come pretty close the correct ratio.

Size - Materials should be chopped into 1/2" to 1 1/2" pieces.

• Larger sizes have less surface to volume and require longer to decompose
• Smaller than that might lead to matting of the materials. Matting reduces the amount of air and will cause anaerobic bacteria to take over (think sewage smells).

Moisture content -

• A compost pile should be about as wet as a wrung-out sponge; damp, but not sopping wet.
• Over watering the pile also reduces the amount of. air in the pile and will produce the same objectionable smell
• Underwatering slows or stops the bacteria from doing their job.

Keeping the heat on -

• Compost piles will begin to heat up in 24 to 48 hours, and the temperature will rise to 160 degrees with a couple more days.
• This heat is evidenced by the steam that escapes when the pile is turned.
• Not turning the pile often enough may let the heat build up to a point where the micro-organisms are killed, and the cycle will have to start over.
• Composting in a bin, possibly with a lid, help retain the heat on cool days.
• A compost thermometer (like this one, also shown non our 'Tools and Books' page) helps you gauge your compost pile's health

Turning the pile -

• Turning the pile so the outsides of the pile are moved to the center, and the center moved to the outside helps control the build up of heat.
• Turning makes sure that all the materials are eventually exposed to the high heat needed to kill weed seeds.
• Bins with removable slats make moving or turn the pile easier.
• I also like the tumbler-type composters since here is no shoveling involved; you crank the handle and the materials are mixed.
• The more often you turn the pile, the faster the process goes.

How fast does it happen? -

• If you turn the pile every day, compost will be ready in as little as two weeks,
• Turning every other day takes three weeks.
• Never turn it and it takes a year.
• Once you start your pile, do not add more materials to it. Doing so only makes it take longer to finish. Start a new pile instead (it will be done about the same time, anyway).

Materials you should avoid include soil (just makes it heavy, dense, and no fun to turn), wood ashes (they are alkaline, and our soil is alreay that way), meat-eaters' manure (possible diseases), and greasey food left-overs.

So what can go wrong?

• If the pile doesn't heat up withon a day, it is too wet, too dry, or lacking green material.
• If it too wet, spread it to dry or add dry material to absorb some of the moisture.
• If it is too dry, water it until it is evenly moist (some turning here is beneficial to even moisture).
• If neither of these is the case, add more green, nitrogen bearing materials, like lawn clipping or animal manures (NOT from meat-eating animals as it may contain diseases).
• If the pile smell of ammonia, there is too much green material and you are losing valuable nitrogem.. Add brown materials like saw dust, shredded paper, etc.
• If you get that sewage smell, the materials have matted together, or are too wet.

So why should you go to all this trouble?

• You are turning 'waste' that would go the landfill in to valuable amendments
• By making your own fertilizer, you save money and the oil and energy needed to make commercial chemical fertilizers
• You can make compost in 2 weeks
• You destroy many weeds and disease organisms

Need to know more? Here are some other publications about composting you may find handy...

USDA National Agricultural Library, Alternative Farming Systems Information Center - Compost and Composting This site has links to some great resource material.

NC State University's Center for Environmental Farming Systems - Composting on Organic Farms

UC Extension's Making and Using Compost in Organic Agriculture

North Carolina Cooperative Extension's list of composting resources