The Bare Bones of Composting

Since early December, the compost pile at the back of the vegetable garden has been a frozen cube of organic matter in various stages of decomposition, covered for four months with a thick blanket of snow and ice.  Now, mid-April, twenty miles inland from the midcoast of Maine, warm rains and 60 degree days have started the thaw.  By the first of May, the microbes that do the heavy lifting in decomposition will be hard at work, finishing the job they started last year.

Composting can be rigorous science for those gardeners interested in calculating carbon:nitrogen ratios and keeping a daily log of the compost pile’s temperature, turning the pile when it starts to cool.  Or it can be a more laid back, hit-or-miss activity in which you add to the pile whatever is available and turn the pile whenever you have the time.  I’m of the later school, a laissez-faire type of composter, and so the following advice presents the bare bones of composting.

Piles and Bins

Any productive compost pile must meet certain characteristics.  It should be large enough to retain heat but small enough to allow air and water to penetrate to its center; three feet in all directions seems to satisfy this requirement best, but there are many variations.  It should also be constructed to maximize air and water penetration throughout the pile.  Beyond these features, however, compost piles take many forms.

Tom McIntyre, hard at work moving compost down the line.

Tom McIntyre, hard at work moving compost down the line.

Tom and Jan McIntyre, gardeners on Mt. Desert Island, Maine, have perfected the pallet system of composting.  On the edge of their garden a row of wooden pallets presents a time line in the creation of compost from a mixture of garden weeds, finely chipped woody materials, grass clippings, and seaweed.  On the pallet at one end of the row, the elements of the mixture are still recognizable.  Looking down the row, the contents of the pile become more and more homogeneous until, on the final pallet, a mound of mostly dark crumbly compost sits ready for screening.  When finished compost is removed from the end pallet, each pile is pitchforked one pallet forward.

Screening compost through screen wire.

Screening compost through screen wire.

The compost taken from the end pallet in this system is screened through a one-inch mesh screen.  Anything that does not pass through the screen is returned to one of the piles at the front of the line for further decomposition.

Simple in construction, the McIntyre pallet system ensures frequent turning of each pile as it is moved down the line.  It also provides maximum exposure of each pile’s contents, including the bottom layer of the pile, to air and water.

Tom and Jan are reluctant to include kitchen vegetable scraps in their pallet composting system.  Like Marjorie’s Garden, The McIntyre garden is surrounded by woods where raccoons and skunks abound, so leaving vegetable scraps out in the open would be a sure draw for these nighttime looters.  Vegetable scraps are composted in a closed container.

Elaborate but functional, the Atwater compost bins were built to last several lifetimes.

Elaborate but functional, the Atwater compost bins were built to last several lifetimes.

Nate and Berta Atwater care for a beautiful coastal garden in Little Compton, Rhode Island.  Berta calls their four-bin composting edifice her folly.  I disagree: It is large, but it is also functional.  And it is constructed to last for generations.  Built from redwood timber, each of the four connected bins has removable front panels that are ventilated, as are the side, back, and internal walls.  The roof shades the compost piles, preventing rapid drying, but also reduces the amount of rain falling on the piles, so Nate adds water with the garden hose as needed.

Simple but functional, the wire compost bin maximizes air circulation.

Simple but functional, the wire compost bin maximizes air circulation.

Composting in Marjorie’s Garden is conducted in two simple wire-frame bins, each measuring 3 feet in all dimensions with side panels that separate for easy moving and storage.  They stand side-by-side at the back of the garden.

Mixing Greens and Browns

Decomposition occurs quickly when the pile’s carbon to nitrogen ratio (C:N) is approximately 30:1.  This is accomplished by mixing “browns”, the high-carbon materials (C:N of 50:1) such as straw and dry leaves, in roughly equal amounts with “greens”, the high-nitrogen materials (C:N of 15:1) such as composted livestock manure, seaweed, and grass clippings.  (I know, manures are not green, but they are high in nitrogen.)

Ideally, the gardener has stockpiles of both greens and browns that can be added in alternating six-inch layers until the bin is full.  More realistically, both greens and browns are added to a pile as they become available, a process that provides limited control over the C:N ratio.  To help keep the C:N ration in balance, we keep a supply of dry shredded leaves on hand to boost the carbon level and a supply of composted goat manure to boost the nitrogen level, adding one or the other as needed.  For example, whenever I add a bucket of kitchen vegetable scraps (high in N) to the pile, I cover them with an equal volume of leaves.  If I add a wheel barrow of chopped sunflower stalks (high in C) to the pile, I cover them with composted manure.

Building the Pile

When starting a compost pile for the first time, start by turning over the soil beneath the bin to provide easy access to the pile for earthworms, ground beetles, and microbial agents of decomposition.  Because a compost bin in full sun will easily dry out, slowing down decomposition, locate your bin in a well-drained spot with partial shade.

If possible, start the pile with a 12-inch layer of fluffed straw – not hay, which is full of weed seeds.  The straw, the hollow stems of harvested grain, is stiff enough to resist compaction and will allow air to enter the pile from the bottom.  Follow with six inches of fresh grass clippings, composted livestock manure, vegetable and fruit waste, or seaweed collected from the high tide line.

Continue building the pile with alternating six-inch layers of high N materials followed by high C material.  Chopping bulky ingredients, including garden weeds, seaweed, and vegetable and fruit peelings, increases the surface areas of these ingredients, enabling bacteria and fungi to work more efficiently.  Be sure to water the pile thoroughly as each layer is added.

Success in composting is measured with a compost thermometer.  A well-constructed compost pile heats up as bacteria do their work, reaching a peak between 90 and 150° F, and then starts to cool.  When the pile returns to ambient temperature, it should be turned so that the least decomposed material on the cooler outside of the pile is moved to the middle.  While turning, water the pile to the consistency of a wrung-out sponge.  Within a day or so, the temperature in the middle should start to rise again.

The Laissez-faire Compost Method

Finished compost, Black  Gold to the gardener.

Finished compost, Black Gold to the gardener.

We start out the gardening year with one of the bins half full of garden waste, most of it accumulated in late autumn as we cleaned up the garden beds for winter.  On top of this, over the course of a week or two, we add layers of composted goat manure, green grass clippings, shredded leaves, and seaweed collected above the tide line at a local public beach.  When we’re done, the compost thermometer thrust into the middle of this pile will read above 100 degrees in a few days.

Whenever the kitchen compostables bucket is full, we bury its contents in the supercharged pile.  Garden clippings and weeds (except for perennial weeds such as quackgrass that will survive thermonuclear explosions) get tossed on top.  When the pile’s temperature drops below 90 degrees, we turn the contents into the empty bin, adding grass clippings and/or composted manure in layers.  Again, things get hot quickly.

Back and forth through the summer, the compost pile changes bins.  If we need a little compost, we simply take it from the lower half of the old pile as we change bins, screening it through one-quarter-inch hardware cloth to remove anything that has not fully decomposed.  Coconut shells, corncobs, and pinecones take forever to rot!

I know gardeners who are hooked on composting.  They keep records of the pile’s temperature and know the carbon:nitrogen ratio of every ingredient that goes into the bin.  They have a hose dedicated to watering the pile.  They insulate their piles in winter to keep them cooking longer.  They claim bragging rights to the quickest turnover in converting raw materials to black gold.  I’m pretty sure I could be one of these gardeners if I had more time on my hands.

And I know gardeners who build their compost piles on top of the ground, no bin.  If the kitchen waste on top of the pile is too tempting to skunks, they take the time to turn the pile or at least throw some straw on top.  The pile gets watered when it rains.  They don’t own a compost thermometer.

Most gardeners compost between these two extremes.  The mixture of materials may not be precise, the bin may not be elaborate, but sooner or later, there’s compost.

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About Reeser Manley

I was born in Laramie Wyoming but moved to the southeast at an early age. I was educated through my B.S. in Biology in the Columbus, Georgia area, then crossed the Chattahoochee River to earn my M.S. in Botany at Auburn University. For the next ten years, I worked as Horticultural Manager for the George W. Park Seed Co. in Greenwood, S.C. At 40 years of age, I decided to return to graduate school and in 1994, I earned a Ph.D. in Horticultural Science from Washington State University, Pullman, Washington. Fast forward through 10 years at university (7 at UMaine, Orono) and you find me teaching high school science in Eastport, Maine, the edge of the world, and writing a weekly garden column for the Bangor Daily News. My new book, The New England Gardener's Year, a Month-by-Month Guide for Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, and Upstate New York”, will be published later this year by Cadent Publishing. You can learn more about the book by visiting its Facebook page: http://www.facebook.com/pages/The-New-England-Gardeners-Year/187285218055676.)