Standing Around the Compost Pile

We are writing this in early July, but the weather has finally turned into the old-fashioned dog days: hot, wet, and humid. Our garden at the Craven Research Center is developing—late but pretty well. Tomatoes, snap beans, eggplants, bell peppers, and okra are looking good. 

In August, it is hard to talk about working in the garden. It’s just too hot! We at the Craven Center are planning to build a composting structure sometime after the weather cools off. Composting fits well with our current ideas of recycling; you can recycle the plant remains and much of the kitchen scraps instead of asking the city to dump it all in a deep hole. Try to hang in with me while I talk about the principles of composting, which are a bit dull but offer a much better approach to overly simple instructions. Friends, there isn’t any proper way to compost; it all depends on your situation and the time you are willing to devote to it.

Composting is much more than recycling. It is not quite, and much more valuable than, natural fertilizer, involving a series of processes in the decomposition of organic material, from dead tomato vines or leftover gumbo down to the remainder of a few inorganic elements. Of course, the beginning and end results are not quite what we want, but compost is more of a process than a simple material.

ANNE: I do have a little experience with composting. Our last house came with an established compost pile, perfect for us amateurs. I took care of contributing the kitchen scraps, while my husband Michael was in charge of adding the yard scraps. I’m only learning now how unimaginative I was with my kitchen scraps! I set aside fruit and vegetable bits for the compost pile, but leftover gumbo? When I asked Leon if anything was off-limits, he said glass and metal, adding that even chicken bones will decompose pretty well. This might be old news to most of you, but for this novice it was eye-opening.

LEON: Now I will get a little technical about the actual composting process. The soil in your yard contains thousands of kinds of microorganisms: bacteria, fungi, and other tiny creatures. Some are very useful in composting, while others are just there. I won’t bother you with scientific names; it is easier to just call the different groups by letters of the alphabet. Group A works on the easily decomposed material such as sugars and starches. When they run out of food material in the pile, they starve to death and group B starts on the next, more easily consumed material, plus the bodies of the poor, dead group A critters. This sounds gruesome, but this sort of semi-cannibalism is important to the final compost. After group B runs out of food, they die and group C begins to work on new material, plus the bodies of A and B. If you let the process continue to the end point, the remains will consist of a few inorganic elements that the plants can use for growth.

This decomposition process continues with the various groups of organisms working at the same time but in different parts of the pile. Broadly speaking, good loose compost is composed mainly of the microbial remains in all stages of the decomposition process. The actual fertilizer value of good compost is rather low; it usually contains about 1.8% nitrogen on a dry weight basis. The phosphorus and potash contents will vary but are also generally low. The reason for this is simple. Microorganisms use the plant and animal materials to obtain the energy and nutrients for their body tissues. This is the key point about composting.

I need to mention the carbon/nitrogen (C/N) ratio. It isn’t really an accurate term, but those are the elements being used. Carbon refers to the carbon in carbohydrates such as sugars, starches, and cellulose. The carbohydrates are the source of energy that microorganisms use to build their body parts; carbon alone would be of no value. But the little critters also need nitrogen compounds to build amino acids and proteins. Again, elemental nitrogen is a gas that is of little value to plants. Putting all of this together, we can calculate that the body parts of microorganisms consist of about ten or twenty parts carbon for each nitrogen element (1.8% nitrogen on a dry weight basis).

Now we can get to the more applied information. The carbohydrate content of grasses and similar plants is too high for the C/N ratio that is suitable for microbial growth; however, a pile consisting of mostly kitchen scraps will probably have nitrogen levels that are too high. The microorganisms can use the nitrogen, but the excess will go off as ammonia, and that doesn’t smell very good. Maybe I should add that the sulfur content of garbage is often also high, and sulfur gas compounds smell so bad that the neighbors will complain. The basic principle here is that you should try to have a good C/N ratio for the compost: too little nitrogen slows down the composting process, while too much produces ammonia. You also need to know that the microorganisms that produce good compost need oxygen and a little water. The center of your compost pile will get very hot and will use the oxygen too fast, so you will need to stir it occasionally.

So here is my model for building a good compost pit. It probably won’t fit your needs but you now know enough about the process to make your own decisions. Select a rather shady spot in your backyard and plan on having two compost piles, A and B, with a wall dividing them. You may want to build a wall around three sides of the compost site, just for appearances. The wall will be made from any material you choose and should be around three feet high. For my example, piles A and B should be around three feet wide by five feet in length. Now, dig the soil in each pile to a shallow depth—maybe six or eight inches. Start the compost by putting the material—primarily the old vines and plant material that you take out of the garden when a crop is finished—in pile A, adding a little nitrogen fertilizer (like kitchen scraps) if you have a lot of grass, and covering it with soil from pile B if it smells of ammonia or sulfur. You might add a little phosphate fertilizer; it will help sometimes.

Keep the pile damp but not too wet and wait a few weeks before digging into the center to see if it is too hot. Under warm conditions it may reach as high as 170ºF but will probably be lower. While a temperature of around 130ºF will kill most weed seeds, it will only kill those in the center of the pile. As a rule, don’t put weeds that have gone to seed in your compost.

Now for the important question: how do you know when the compost is ready to use? The best answer is to use it when you need it. A good guideline is that the compost is ready when you see earthworms growing in it. Worms are of little value in creating compost but are a good sign that you have done your job well. When the compost is ready in pile A, start using pile B, but put a little compost from A into the base to sort of seed the pile with the proper microorganisms.

We began this account by saying that compost is not quite, but much more valuable than, natural fertilizer. Now I can explain why: microorganisms decompose organic material and release fertilizer. In the decomposition process, they produce a sticky, gum-like substance that binds soil particles together and gives the soil much better structure. You can spread compost on the raised beds or work it into the soil. The improved soil structure will allow better aeration and better drainage.

ANNE: We moved into this home less than a year ago. Here’s hoping that our new neighbors will forgive us if our compost pile’s carbon/nitrogen ratio isn’t perfect at first. We’ll get there.