backyard compost

Backyard composting

The compost center is the soil-building factory of productive backyard ecosystems. It’s where household by-products and low value organic materials are processed into higher value, micro-biologically active humus by teams of bacteria, fungi, nematodes, and earthworms. The ability to produce one’s own compost is of huge significance to the economic performance of backyard food production. Consider the $60 – $140+ price tag per yard of bulk compost delivered to your home, or if bought by the 20-quart bag, the price can be $300 and up for a yard of compost.

Backyard compost bin make from stakes, pieces of pallet & chicken wire

Backyard compost bin made from stakes, pieces of pallet & chicken wire

It’s sometimes argued that at the individual home scale the amount of organic material is too small to compost properly, that it’s unsightly, smelly, and should be done ‘elsewhere’. Since it takes energy in the form of transportation fuel to move organic material from our homes to ‘elsewhere’, and we then have to travel back to ‘elsewhere’ to buy back our organic material in the form of compost, I’ll argue that it’s economically and environmentally prudent to examine ways to compost at home that address these issues. I have no doubt that commercial & municipal scale compost operations are necessary, valuable, and play an important role serving restaurants, businesses, hospitals, institutions, and other gathering places that produce organic wastes appropriate for composting at scales sufficiently large  enough to warrant the expense of transportation.

First, let’s consider the processes of composting. There are inputs to the process, laborers, essential components, and an output. The inputs may be kitchen scraps, plant material from the garden, coffee grounds, grass clippings, hay, straw, animal manure, woodchips, soy ink newspaper, sawdust, cardboard, fallen leaves, hair clippings, nail clippings, lint, and other organic by-products. In the backyard compost system, it’s wise to omit meat  & dairy waste. In this instance backyard piles are indeed generally too small to ensure that they will heat up to sufficiently process these materials without going rancid. Buying boneless cuts of meat and watching expiration dates closely so you eat all that you buy can go a long way to minimize these products in the waste stream.

Inputs are categorized as carbons (or browns), which are materials that have a carbon to nitrogen (C:N) ratio of 30:1 or more such as dry hay, leaves, sawdust, and newsprint and nitrogens (or greens), which are materials that have a C:N ratio of less than 30:1 such as vegetable scraps, chicken manure, and green vegetation. It’s ideal to build a compost pile with a C:N ratio of 30:1. Here’s a table below of some of the most common compost inputs and their C:N ratio. Nature is highly variable and these values are not absolute but do provide a useful guide. It is not of absolute imperative that the ratio of the pile be exactly 30:1. The reductionist perspective of calculating out the C:N ratio to the microgram is unnecessary. Composting rewards good approximation and intuition.

Material

% Carbon

% Nitrogen

C:N Ratio

Alfalfa pellets

40.5

2.7

15.00

Blood Meal

43

13

3.31

Cottonseed Meal

42

6

7.00

Soybean Meal

42

6

7.00

Legume Hay, dry

40

2.25

17.78

Nonlegume Hay, dry

40

1.25

32.00

Fresh manure, cow

15

0.8

18.75

Fresh manure, horse

30

0.75

40.00

Fresh manure, laying hens

15

2.25

6.67

Fresh manure, broiler chickens

25

1.6

15.63

Wheat or oat straw, dry

48

0.5

96.00

Grass clippings, fresh

12.5

1.5

8.33

Fallen leaves

25

0.7

35.71

Newspaper or cardboard, dry

40

0.1

400.00

Woodchips or sawdust

37.5

0.1

375.00

Coffee grounds

25

1

25.00

Vegetable wastes, fresh, leafy

10

1

10.00

Vegetable wastes, starchy

15

1

15.00

Kitchen scraps

15

1.5

10.00

Fruit wastes

8

0.5

16.00

Seaweed, fresh

10

1

10.00

Weeds, fresh

15

2.5

6.00

If I make a pile out of only fresh leafy vegetable waste (C:N = 10). This pile is significantly under the 30:1 target and the pile will tend to be slimy and smelly. If instead I make a pile out of only dry wheat straw, with a C:N ratio of 96:1, I will be significantly over the 30:1 target and the pile will tend to be dry, crumbly, and will break down very slowly, if at all. Now, if I build a pile out of 2 parts fresh leafy vegetable waste and 1 part dry wheat straw (by weight, not volume), the C:N ratio with be about 27:1 which is close enough for a pile to break down rapidly and evenly.

Why do piles with different C:N ratios behave differently? The answer lies primarily with the laborers of the compost factory. The workforce consists of a diverse collection of organisms including bacteria, fungi, nematodes, and earthworms. There are billions of microorganisms in a teaspoon of living soil. These critters are absolutely essential to life on earth. As our understanding of soil has developed, we have learned that it is not simply the presence of the appropriate proportions of elemental nutrients that produces fertile soil, it is the presence of trillions of living micro-organisms living, dying, eating, decaying, cycling materials, and all the while making nutrients available to plants that leads to vital, fertile soils.

Compost thermometer in a backyard pile at 110* F

Compost thermometer in a backyard pile at 110* F

As the micro-laborers go about their lives, they are happy to break down complex organic compounds into their elemental constituents, of which carbon and nitrogen are by far the most plentiful, but these workers have a few basic requirements, namely water and oxygen. When the C:N ratio of a compost pile is less than 30:1, there is a proportionate excess of nitrogen and lack of carbon. This is the stinky, smelly pile. Anaerobic bacteria thrive in this moist, oxygen deprived environment, producing hydrogen, ammonia, organic acids and methane . When the C:N ratio is greater than 30:1, there is not enough nitrogen for the microbes to build their bodies at the rate they would like and populations to not grow large enough the process the material quickly. This results in the dry, crumbly, unproductive pile. The 30:1 ratio provides the optimal balance, providing an environment where there is sufficient fuel & building material for the microbes to do their work as they like and for their to be enough air infiltration into the pile to keep aerobic populations in charge. This balanced pile will smell earthy and generally pleasant.

Just as we would not last long without water and oxygen, soil life also need them. In arid climates it may be necessary to add water to piles at times, but in most temperate climates rainfall provides enough moisture. Oxygen is relatively ubiquitous on the surface of our planet, although as I’ll talk about next in the “what doesn’t work so well” section, we sometimes go to lengths to keep out the elements that are essential to healthy compost.

We have a belief in America that you can’t do something until you buy the something you need to do it. Therefore it’s not a surprising that many people want to buy a composter in order to start composting. Which is understandable, but many “composters” often look like these;

 

Which is a problem because these “composters” don’t work very well at producing compost. In addition they require resources to build and transport when suitable alternatives exist locally, such as reclaimed wood, hay bales, shipping pallets and more. We need to ask about bins we may buy, how well is water going to get in? How well is oxygen going to circulate? There may be a few vents but most have not nearly enough to allow for rain water to percolate freely or for sufficient oxygen flow. As a rule of thumb, if you wouldn’t put your cat or dog in it for say, an hour, you shouldn’t attempt to compost in it either.

The process we call composting has been happening for 500 million years, recycling organic material on the planet for all terrestrial life that has ever existed. It’s therefore not advisable or necessary to use a plastic space capsule to do it.  A pile on the ground will compost. Anything we do beyond that should be done to improve compost outcomes and integrate composting with our human desires for order and a sense of place. We don’t want to sacrifice function for form, because then what’s the point of doing it at all?

Why don’t I compost in a pile on the ground? The dog would eat it, probably get sick, and nearby skunk, raccoon and squirrel populations would usher me down a short, slippery slope to a backyard compost hell-scape. The dog would incur vet bills, the wild animals would eat into the the amount of compost I have left over for my plants, and both would spread the heap around. So I need a solution. I have tried using plastic compost bins and while they provide a place to put food scraps for a year or two, they have not generated a useful compost. At the conclusion of the experiment I was left with the liability of a rather nasty cube of mostly intact vegetable matter enclosed in a plastic shell.  Out of pocket cost: $50. Compost for the garden: 0.

There are other options between the free-for-all hell-scape and the garbage-pod space capsule approaches. In order to consider these, let’s examine the human ecosystem as it relates to compost production and use. We eat every day for the most part and thus most of us generate kitchen scraps and other organics for composting at a small but steady rate. This is a challenge to the optimum construction of a compost pile, which is to build a pile all at once at a minimum size of 1 cubic meter, mixed to approximately our 30:1 C:N ratio. Then we leave the pile to break down, possibly turning and churning the pile. In an optimal pile, total breakdown is around 3-4 weeks, during which time we do not want to add fresh organics, but we are still producing them at the same steady rate.

In the backyard, we want to bring out household organics (which are generally nitrogens) when the household storage bucket is full, which is every few days, it really depends on your household. Then we want to spread them evenly in the bin, adding a layer of carbons and repeating with more nitrogens until we have a full bin. To do this we need a place nearby to store the carbons. This works until the first bin is full. Then we need a second bin to use while the first one composts down. A third bin is the best option; 1 that has finished composting and is used as needed, 1 that is actively breaking down, and 1 that is being built. Bins have been made of shipping pallets, cut apart and re-assembled to the desired form, various wire supported by stakes driven in the ground, hay bales stacked to form the sides and back of a bin with 1 or 2 dropped in front as a “door”, stacks of concrete blocks, and sod from the yard.

Austrian permaculture teacher and practitioner, Sepp Holzer, offers even another approach. No bin is built at all. Instead, two parallel rows of Holzer raised beds are built and organic material is placed in the space between. Holzer’s beds are shaped roughly like windrows of wood and soil. Holzer’s method is to fill the space between the raised beds with compostable material and then grow crops in this space, back-filling down the row a little at a time. As the row becomes full, the oldest material is ready to be removed and used elsewhere in the garden. In this way Holzer gets a yield of vegetables and compost with minimal input of energy or materials.

The earlier mentioned skunks, raccoons, squirrels and other urban scavengers will undoubtedly find your pile eventually. Your personal desire for order will dictate the lengths you take to fence these critters out of your bins. Squirrels frequently visit my bins and while they sometimes leave a corn cob in the yard, they generally keep their activities confined to the bins so I’m willing to trade a little compost for their services of tilling and mixing my compost. Burrowing animals may try to come in from below. If this is a problem, wire screening can be buried 6″ down and 6″ out all around the bins, forming an L that burrowers will be turned back by.

Using design and planning to account for the function of soil and human ecosystems it is possible to produce compost in a way that supports the soil health, efficiently makes use of organic wastes generated by households, manages animal interactions, and creates the foundation for a prosperous backyard garden.

Finished compost in backyard pallet bin

Finished compost in a backyard bin made from shipping pallets