aerating a compost pile

My Pile: Air Today, Gone Tomorrow

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Sure enough, like washing your car or forgetting your umbrella, hand watering the garden plantings the other day was all it took to prompt a series of early-summer rain squalls to pour much, and much-needed, water upon the backyard and my pile.

This evening after work I tip-toe across the sodden lawn to check in on my pile. Mowing will have to wait until the grass dries out, and with backyard cookouts postponed, the kitchen bucket has been slow to fill with its summertime surplus of watermelon rinds and silky corn husks.

My pile looks like an upturned bowl of brown mush. Though the recent rain has likely soaked down only a few inches through the sodden outer layer, I know that much of what lies underneath is saturated with moisture from another source: Grass clippings. I read in Compost Fundamentals, that grass clippings are more than 80 percent water, and, more worrisome, that a compost heap that is more than 70 percent water can quickly devolve into a stinking, anaerobic mess.

My pile is drowning in grass.

“Aeration is necessary in high temperature aerobic composting for rapid odor-free decomposition,” I further read in Compost Fundamentals, a website managed by the Washington State University Extension. “Aeration is also useful in reducing high initial moisture content in composting materials, which reduces the pore space available for air as well as reducing the structural strength of the material. This permits greater compaction and less interstitial or void space for air in the pile.

“If foul odors of anaerobic and putrefactive conditions exist when the pile is disturbed either by turning or by digging into it for inspection purposes, turn the pile daily until odors disappear. No matter how anaerobic a pile may become, it will recover under a schedule of daily turning that reduces moisture and provides aeration.”

I’ve tossed and tumbled the influx of fresh clippings with clutches of old and dry leaves, but even so, the clippings tend to compact into a suffocating layer, prompting a riot of hothouse bacterial growth that sucks up all the available oxygen.

Tonight my pile needs bailing out. I consider plunging into it with the pitchfork, but that project is too ambitious for the time I have on hand. I decide on a more surgical approach, and have just the tool for it: A seven-foot length of metal rebar I use to give my pile needed gulps of air, more like an emergency tracheotomy than a full-scale resuscitation.

“Some prefer to manage a hot or thermophilic pile for several weeks, then stop turning the pile letting mesophilic organisms take over, which encourages fungi and actinomycetes development. Fungi and actinomycetes are the best decomposers of woody matter, such as sawdust or branches. Actinomycetes gives compost the earthy smell—like that of the forest floor.”

That’s pretty much my goal for tending a backyard compost heap — to have it exist as a fragment, a fragrance, even, of the natural process of decomposition, only speeded up by human hand.

So I grab the rod of iron rebar from its resting place against the back fence and gingerly make my way up atop the log containment walls to give my pile a good poke deep inside.

The length of rebar is my divining rod. Like hand-watering, aerating my pile with the ribbed metal rod gives me a kind of kinetic, x-ray insight. With each successive thrust through the top layering of matted leaves, I not only create passageways for fresh air, but also get fresh feedback about what’s going on inside and out of sight. It’s another tactile, probative, way of staying in touch with my pile.

 

The rod of iron rebar I use to poke my pile is about 7 feet long, and makes a handy tool for aerating it through and through.

The rod of iron rebar I use to poke my pile is about 7 feet long, and makes a handy tool for aerating it through and through.

“To compost well, you must ‘think like a microbe’ and create the best environment to support microbial activity,” I learn from Florida’s Online Composting Center, managed by the University of Florida. “Microbes have similar environmental needs as people: water, air, comfortable temperatures, and food. Because they reproduce so quickly under ideal conditions, microbes may deplete the available oxygen through their activity. Therefore, it is important to aerate your compost.

“You can aerate your compost by turning it. This directly incorporates oxygen into the pile. You can aerate by adding bulky items. Bulky items provide air channels so that oxygen can flow into and through the compost. Bulky items also keep the pile from settling and compacting, which could restrict oxygen flow. Bulky items include oak leaves, pine needles, chipped twigs, and straw. You can aerate by probing the pile with a piece of rebar or an aeration tool. Simply probe the devise in several places in the pile. This will create passageways for air to enter the pile.”

Though I’ve dug out both front and back walls of rotting leaf mold to add cavalcades of fresh green manure to its sloping sides and on top, the epicenter remains out of reach with the pitchfork. Probing my pile with the rebar is like sticking a knife into a loaf of bread baking in the oven. I can tell that my pile is well on the way of becoming a uniform heap of ripening compost, though the rod meets more resistance is it pokes through to the untouched core, the undiscovered country.

The tip of the rod emerges from the mix steaming hot, and surely these thrusts give it much needed air. My probing takes only a minute, the exertion balanced by the trickier task of not slipping off the slick tops of the log walls. As much as it needed the recent rain, I know my pile also needs big gulps of air, and after a couple dozen thrusts from above and at ground level, it’s now riddled with slender shafts of space through which to breathe.

One of the blessings of my pile is that it’s as low maintenance as I want it, or need it, to be. It places few demands on my time, asks nothing of me, and accepts only and all of what I care to give it. And best, the thing it needs most is what’s most valuable and free and easy of all to give: Air.

My Pile: Breath of Fresh Air

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It’s a Sunday, and in advance of the next-up storm, which the forecast says will be a mix of freezing rain and a few inches of snow, I head out to my pile.

It’s done well to slough off its latest covering of white, nearly a foot of wet, heavy snow delivered two days ago. Wide vent holes have opened up across the heap, and once again the top of my pile has sagged deep into itself.

 

My pile sloughs off the latest snowfall, creating vent holes over hot spots within.

But I can’t resist fussing with it further. Using the wide-mouth shovel, I clear the thick caps of snow from each side of the log walls, heaping the snow into the cavities created by the melting from within. I then scoop more snow from the sloped front side, which faces north and is still swathed in deep drifts. I then turn the shovel upside down and slice and dice down through the remains of the crusty snow caverns and new chunks of added snow.

The result is a topping of cottage cheese snow, about six-inches thick, for my pile to work its way up through anew.

Heaping my pile with more snow.

Heaping my pile with more snow, at the risk of dousing the biological process that keeps it burning within.

The log walls cleared of most of the old snow, I grab the rebar rod, clamor atop and punch a couple dozen holes down through the pile. I focus on reaching the “cold” areas where the heat from within hasn’t percolated upward. My goal is to activate as much of the pile as I can to give my pile fresh gulps of air to offset the weight and soddening effect of the water within snow. Sort of like doing acupuncture, only with a half-inch metal bar.

Aside from the shoveling of my driveway and porches and chilly walks along the beach with the dog, such tinkering is my exercise for a winter day. In short order my arms are heavy and burning with the effort of plunging the length of ribbed iron again and again through the resisting layers matted leaves below. The working end of the bar heats up before long, and the jousting releases a faint whiff of rotten egg.

In the aptly titled “Let It Rot! – The Gardener’s Guide to Composting,” Stu Campbell explains:

“To grow and multiply, microorganisms need four things: (1) an energy source, or carbon; (2) a protein source, or nitrogen; (3) oxygen; and (4) moisture.

“Oxygen is required by many of the microorganisms, especially the most efficient bacteria, called aerobes. When not enough oxygen is available, the aerobes cannot survive and the anaerobes take over. Once this happens, decomposition slows by as much as 90 percent.

“The aerobe can do a more complete job of composting than can the anaerobe. As the aerobe and its cohorts break down carbon compounds into carbon dioxide and water, they are also producing a lot of energy. This gives them a distinct advantage, because they can use this energy to grow that much faster themselves and decompose that much more material. At the same time, and no less important, they excrete plant nutrients such as nitrogen, phosphorus, and magnesium, to name just a few.

“Meanwhile, back at the airtight heap, the anaerobes struggle to produce carbon dioxide, water, energy, and nutrients, too – although in much smaller quantities when compared to the aerobe’s performance. They also produce a lot of useless organic acids and amines (ammonia-like substances), and in some cases are toxic to plants. Some of the end products of the anaerobe’s efforts are hydrogen sulfide (which smells like rotten eggs), cadaverine, and putrescine. These last two descriptive names do a great deal to explain the nauseating odor of an anaerobic compost pile. So you see why this book places so much emphasis on keeping the pile well aerated.”

At this point in its life cycle, my pile has all that it needs, save air to keep breathing. There is no timeline for my pile, no order to fill. I could let it slumber in stasis through these days and nights of sub-freezing weather. But where’s the sport in that?

 

My Pile: Breathing Room

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It’s a balmy Sunday in mid-December,  and although the neighbors are busy decking out their homes and yards with holiday lights and decorations, it’s unseasonably warm. With a record high of  near 70 degrees today, I leave my own lights in their boxes in the attic and plan to devote the day to sprucing up the backyard and taking care of outdoor chores.

There’s wood to chop for the fireplace. I roll a few whole logs from the stack of sawed-up maple drying next to my pile. I stand them on end to split into chunks and soon have set aside enough cordwood to burn well into the new year.

Some of the maple logs are too long for the fireplace, or too knotty to bother chopping. But they will make good new replacements for the rotting logs that contain my pile. The two parallel walls of thick old stacked logs also serve as stepping stones for me to clamber up, and several are now too crumbly to safely perch on.

Today I plan to give my pile a good poking, using an 8-ft. length of rebar I snagged a couple years ago from a neighbor’s scrap bin. Standing atop the log walls requires a bit of a balancing act to thrust the bendy section of rusty, ribbed steel down into the heap of leaves.

I roll two new logs into place, improving both the sturdiness of the log steps and giving me new perches to sit on at the feet of my pile. I also like the look, as along the way I’ve also added some rakings of fresh leaves to the top of my pile. There is always tidying up to do in a backyard garden, especially one as active as mine.

Some of the busyness involved in chopping wood and shoring up my pile. Plus, old pumpkins from the neighbors...

Some of the busyness involved in chopping wood and shoring up my pile. Plus, old pumpkins from the neighbors…

My pile is like a sandbox for grown-up play. It offers endless opportunities to make things up in a playful yet industrious way. It reminds me of the forts we baby-boom suburban kids once made in nearby woods or construction sites to fight imaginary cold-war battles.

Which brings me to the rebar I use to poke my pile.

The rusty stick of half-inch steel weighs just a couple pounds, but climbing atop the log walls and thrusting it a couple dozen times into the midst of my pile gives me a good, quick workout. As an aerating tool, it does a fine job of making my pile more porous, for both water and air.

My pile needs to breathe. It may be chockful of dead stuff but it is a living thing, and to sustain the life within it my pile needs air.

“What you are doing when you construct an aerobic (with air) compost heap is creating the right environment for the billions of microorganisms that make the compost happen. Their food is the materials that you put on the heap,” counsels Nicky Scott in “How to Make and Use Compost.”

“A happy heap will have a balance of air and waiter, just like a squeezed-out sponge; the whole surface area is coated in water but there are air spaces in between. If the pile is too dense, squeezing out all the air, then all the beneficial life forms in the compost heap are not going to survive and will be replaced by the ‘bad’ microbes — the anaerobic (without air) ones that are responsible for all the bad odours you get from putrefying substances. This is bad news for your compost and if you put this material on your plants it can be toxic to them. So creating air spaces in the compost is vital.”

Turning, or tumbling, a compost pile is the surefire way to add big gulps of air to the process, but my pile is too big and unwieldy at this point in its life cycle. Using a hand aerator is much like performing CPR — a remedy used after the fact as a short-term fix.

I try to give my pile good lungs from the start, mostly by building it in layers and using plenty of porous material along the way, mostly the hollow reeds of salt marsh grass gathered from the seashore but also armfuls of spent tomato vines and flower stalks from the cutting garden.

Some years the deer allow me to grow sunflowers along the fence bordering the vegetable garden, and come the fall their thick fibrous stalks make excellent ventilation shafts for my pile. The soft centers rot out — think of sugar cane — creating hollow tubes for both air and water to flow.

 

Sunflower stalks, or reedy stems from perennials make good interior highways for air, water and things that creep and crawl.

Sunflower stalks, or reedy stems from perennials make good interior highways for air, water and things that creep and crawl.

Some compost experts advise starting a heap by first sticking a length of perforated PVC pipe in the middle, or a rolled-up tube of wire mesh fence, to serve as a more permanent chimney. I may try that trick someday but for this season will stick with my sticks of sunflower augmented by slender steel.

Jousting with my pile is also instructive.

With a few hard thrusts, back and forth, the rod drives deep into the pile. The rebar ribs make it thrum and give me sensory feedback through the vibrations in my gloved hands.  The rod zings like a tuning fork through a section of dried leaves. It tings like sonar when the blunt end strikes an oyster shell caught up in a collection of seaweed from the beach. What’s that tough but squishy part? The Jack o Lantern tossed in after Halloween?

An old length of rebar makes a good aerator for my pile.

An old length of rebar makes a good aerator for my pile.

I press harder, leaning into the bar of rebar when it meets the resistance of a thick patch of tightly packed mulched leaves. I press on, and when the tip meets hard ground I feel the jarring end note all the way up to my elbows.

Sometimes when I tug the rod back up and out of its tight pathway, jousting with my pile, it wins, and the pole slips through my gloves. I grab tight and pull harder, fearing that one of these days I’m going to stick the shiv of metal right up under my chin.

I jerk the rod free and clear, using its slender wobble like a tightrope walker to keep from teetering off the log wall.

I make a dozen or more thrusts from each side and front and back, varying the angle of entry each time, making a pin cushion of my pile. In my mind’s eye I see each punch hole as a slender tube of air for water to navigate, a superhighway for countless unseen bugs and bacteria to mix and mingle. I’m creating breathing room for my pile.

The piece of rebar also makes a handy thermometer to gauge the temperature of my pile. It's hot to the teuch!

The piece of rebar also makes a handy thermometer to gauge the temperature of my pile. It’s hot to the touch!

The butt end of the rebar glistens with steam. I pull my glove off to confirm: The rod is warm to the touch.

I wonder if the heat is caused by the friction of all my aerobics, so I stick the piece of cooling steel back down into the heart of my pile. I wait a few beats, then draw the end back out to take the temperature of my pile. The bar is hot to the touch. I take it as a good sign that inside my pile is a churning, burning mix of earth, water and air.

It’s smoking hot, my pile.