Remember Col. Bill Kilgore in Apocalypse Now—“I love the smell of napalm in the morning”? Well me I love the smell of compost in the morning. It’s a sweet, ephemeral fragrance, similar to a chanterelle or a Woods blewitt mushroom, and it reliably makes me happy.
Recently I’ve been doing some reading to learn more about one of my favorite processes and to refine my techniques. City compost has some extra challenges. It can’t waste space and it can’t stink, so you have to pay attention to detail. I use three bins, one as a sort of preprocessor, for woody and weedy stuff that I don’t want to put directly on the pile, and two as the working composters. Within that restricted system, I’m trying for maximum completeness, so that I don’t have weed seeds surviving to sprout in my soil and so that all possible nutrients are available to my plants, and maximum speed, so that I can produce as much as possible as fast as possible in a limited space.
Compost making has three main variables: content, temperature, and aeration. Those are the boundaries within which a host of bacteria and invertebrates turn a bit of this and a lot of that into the fragrant, crumbly material that improves soil structure, provides the big three of nitrogen, phosphorus, and potassium, boosts plants’ immune systems, and supplies important micronutrients such as manganese, copper, iron and zinc. Besides all that, it gives a free and honorable resting place for your kitchen scraps, fallen leaves, dead houseplants, and shredded financial papers.
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| No more compost--Claudius is rank enough already |
Composting is a natural process—leaves fall off the trees, browsing deer add their droppings, rain falls, mice tunnel through the resulting moist layers of carbonaceous and nitrogen-rich stuff—and next spring you’ve got another layer of humus to keep the cycle going. Humans have been concentrating that system for agricultural use for thousands of years and writing about it for nearly that long. Shakespeare has Hamlet tell his mother to stay away from the wicked Claudius by saying not to “spread the compost on the weeds/to make them ranker.” Gertrude didn’t do so well at taking that metaphorical advice; I have troubles with it myself in the literal domain. I sometimes wonder if I am composting for the sake of the buttercups more than for the squash.
H.H. Thomas, in the lovely little British guide from 1913, Garden Work for Every Day, does not specifically address compost making, but he does talk about the hotbeds, which use the same principle:
“Leaves alone will make quite a good hotbed, they are more lasting in heat than stable litter, but are not so violent. Undoubtedly the best thing is a mixture of the two. When making a hotbed see that it is trodden very firmly, or the heat will be very violent at first, but will quickly be spent. Instead of forming a large heap and then treading it, let the litter be put on in layers and trodden frequently and well. … Do not use the bed until the violence of the heat has subsided.”
Thomas worked for years in the Baron de Rothschild’s French gardens and of the Royal Gardens of Windsor before turning to writing and editing, so he should know. And his warnings about the violence of the heat are well taken. I recently learned, courtesy of University of Illinois Extension’s excellent series of articles, that three main sets of bacteria are responsible for composting decomposition, each operating in a different temperature range. They are the bridge between the basic compost ingredients—carbon and nitrogen—and the humus that results from their work. As they oxidize this organic material, creating the bacterial equivalent of heavy breathing, the pile heats up. Psychrophilic (psychro is from the Greek word for “chilly”) bacteria start the process. When their work gets the pile up to around 70 degrees F, mesophilic bacteria take over and pump things up to around 100 degrees.
When I headed out this morning, frost was on the grass but a little stir made the compost bin steam—Mesophilia in action. This is also the temperature preferred by Actinomycetes, which it turns out are the ones I have to thank for that smell I like so much. They are “a higher form bacteria similar to fungi and molds,” says Illinois Extension, so the fragrance similarity isn’t surprising. They also get credit for working through my shredded paper and woody Jerusalem artichoke stalks because they can handle the cellulose that is beyond the scope of most of their less-complex relatives.
As the pile gets hotter, the mesophiliacs migrate toward the cooler outer edges where the temperature is more to their liking; in summer this strategy works well since the ambient temperature is likely to be enough to keep them happy, In winter it’s not so successful, one of the reasons winter piles decompose more slowly and less completely. Without major messy effort, I can’t completely mix in the material from the outer edges of my enclosed bins, so the outer reaches tend to lag well behind the inner core.
In the hotter inner regions, thermophilic bacteria pick up the tempo, heating up to as much as 160 F. These are the “live fast, die young, leave a beautiful corpse” members of the composting world. They break materials down rapidly and thoroughly, they kill off weed seeds and pathogens, and they generally burn out after a few days, after which the temperatures drop again and the mesophilic bacteria return to the field.
The thermophilic bacteria are the reason that big municipal composting facilities—with much greater mass and with mechanical systems for moisturizing and aerating, can handle lots of the animal products, pizza boxes, and woody plants that can overwhelm home systems. But having said that, I’ll happily admit that I ignore the warnings against composting cheese, milk, fats, meat scraps, etc., in home systems. They are all organic materials and they rot just fine. The problems they can cause are twofold: smell and varmints. Rotting meat smells a lot worse to us and a lot better to rats, raccoons, and skunks than rotting lettuce does. A determined rat will chew right through a heavy-duty plastic compost bin, and raccoons are skilled lid removers (I once saw one unscrew a gallon glass container). So you do need to be careful. My cats and big silly dog seem to be enough keep away the local rodent population; probably they are so well fed in my neighborhood that they don’t need to take extra risks. But the smell can be an issue. One summer I got carried away with salmon scraps in the compost bin, and the stench was appalling for a few days. But generally there are no repercussions as long as you bury the scraps deep, provide nitrogen for quick bacterial action, and keep the bin mixture aerated.
A far more common source of bad smells in compost is lack of oxygen. If oxygen levels fall below 5 percent, the aerobic bacteria die off and the anaerobic ones move in. This is bad for several reasons. Anaerobic decomposition is much, much slower (and slimier); the nitrogen it produces is often in forms plants can’t use; and it stinks: guess what compounds named cadaverine, and putrescine smell like? You can buy a flashy compost twirler for aeration, but I get by fine by poking in air holes with a piece of rebar.
Another issue for city people tends to be a reliable nitrogen source. You want a ratio of about 30-1 carbon to nitrogen in your starting pile; decomposition will use up carbon and produce nitrogen, resulting, if all goes well, in the ideal 8-1 ratio of the finished product. The carbon is easy—leaves, shredded paper, hay and straw, dry stalks of this and that are all good sources. But avid gardeners can get pretty emotional about their nitrogen. I remember my mother-
in-law, who was definitely not a country girl, practically caressing the buckets of aged cow manure we used to bring from the farm to her splendid Seattle camellias and rhododendrons. “This stuff is gold,” she would say.
In my long composting career I’ve used all sorts of things. Horse manure, our standby during my childhood, has a number of problems. Horses are inefficient digesters, one of the things that makes feeding them so expensive, so their manure tends to be rife with sproutable weed seeds. And since they eat lots of hay, the chances of getting a batch that has been contaminated with broadleaf herbicides is greater than with many other animal manures. On the other hand, the smell isn’t offensive, at least not to me, and that’s a plus in urban neighborhoods. Cow manure is sloppy and a bit stinkier, but it’s good stuff, especially if the animals have been bedded in straw. For a really good manure
source and a really terrible smell, there’s fermented turkey droppings. When I lived in Glen Ellen, California, we used to get it by the truckload from a nearby farm. That stuff created a horrific, miasmic reek that filled the air and clung to clothes and skin. Luckily I was living on up on a ridgetop, hundreds yards from the nearest neighbor. The tomatoes we grew with it were the best I’ve ever had.
Chicken manure is a local favorite in my poultry-obsessed neighborhood. Fresh chicken manure is
very high in nitrogen, too hot to handle for direct application to plants, but able to get right to work on the straw or wood chips that often comprise the bedding. It can smell pretty bad on its own, but it’s not so offensive when mixed. The chicken/wood chip mixture I’m using now from my nice neighbor Kate across the alley is working much better than the horse/straw combo I tried last year. That stuff just sat around month after month; I know it was slowly, slowly breaking down, but I don’t have the space for the patience required.
Another less than successful experience was llama dung (some aficionados call them llama berries, but I’m not going there). Llamas are browsers, more like goats and camels than like cows, and their manure is correspondingly more concentrated and less seedy than that of cows and horses. It barely smells at all. My problem was getting it moist enough to make a home for the bacteria. I’m guessing that their evolution up on the arid
altiplano makes them efficient retainers of all available water. The clumps sat for months unaffected by the moisture in the rest of the pile. I had to soak them in buckets of water, and that’s just too much work. Eventually I loaded up the remainder of my pile of dung plus straw and used it to mulch my raspberries for the winter. I’m figuring a bunch of rain and some freezes and thaws will eventually make it give up its integrity and head back into the carbon cycle.
Coffee grounds are the new compost savior around here, where there’s almost literally an espresso stand on every corner. The Buzz Inn stand in my neighborhood puts out its daily blend of espresso disks, coffee grounds and filters, lettuce, eggshells, and the odd orange peel and tomato slice in kitchen garbage bags. It is a first-rate composting material—good nitrogen ratio/decent amounts of phosphorus and potassium/good water retention—it’s got it all. You can also put it right on the garden as mulch, but then your yard smells like stale coffee. So I put most of it in the bins. I do, however, mix it with
the fallen leaves I leave for mulch around the ornamentals and with the sawdust I used to acidify the blueberries. On its own, sawdust will pull nitrogen that’s already in the soil to aid its own decomposition, and that’s counterproductive. I’m hoping that it can grab the nitrogen from the coffee grounds instead.
I’ll admit that I’m sometimes feel just a little embarrassed about the intensity—not to say violence—of my connection with my compost piles, so I was delighted to find the following quote from Bette Midler, aka The Compost Queen.
My whole life has been spent waiting for an epiphany, a manifestation of God's presence, the kind of transcendent, magical experience that lets you see your place in the big picture. And that is what I had with my first compost heap.
Further Reading
http://web.extension.illinois.edu/homecompost/science.html
http://www.sunset.com/garden/earth-friendly/starbucks-coffee-compost-test-00400000016986/
