Composting: It seems like a simple enough concept. Throw kitchen scraps and yard waste into a pile, wait for it to decompose, and eventually harvest a rich, organic fertilizer to feed your garden. But as with just about anything from billiards to bagpipes, once you scratch the surface on the subject of composting you discover a whole complex world of conflicting opinions and advice on the right way to go about doing things. Some of the materials available in books or online almost make the act of composting seem like a full-time venture.
The truth is, anyone can compost, and it doesn't have to be a complicated affair. In an attempt to simplify things for the beginner composter, here I'll explore some of the questions I've stumbled upon in my own composting journey.
One of the first things an aspiring composter needs to consider is where to keep the heap and how to contain it. There are dozens of fancy compost bins and tumblers on the market, which can easily trick impressionable gardeners like myself into believing successful composting demands a serious cash investment. Luckily, this isn't the case. Buying expensive composting accessories is fine if you have the means, but constructing a functional compost container need not be expensive or time-consuming. Many gardeners have tremendous success with simple designs of scrap wood and chicken wire or other inexpensive materials. For those concerned about critters, more secure compost containers can be made by simply punching holes in a trashcan or plastic bin.
Ultimately, all you really need as far as containers go is something that allows for sufficient air and water circulation and a design that makes it relatively easy for you to turn the heap from time to time and retrieve finished compost as needed. Commercial composters are often designed to make these tasks simpler and more convenient -- tumblers, for example, make turning the pile a breeze -- but they certainly aren't necessary. If you're restricted by funds or prefer a DIY approach to gardening, there's nothing wrong with keeping it simple.
Size Does Matter
Composting guides often emphasize temperature; the collective metabolic activity of microbes digesting organic matter can generate a tremendous amount of heat, and under the right circumstances, a compost heap can reach temperatures in excess of 150F -- the kind of heat you can warm your hands over. High temperatures expedite the decomposition process and kill off pathogens and seeds from any weeds you've tossed in.
If you've been composting for a month or so and haven't noticed any significant temperature change, it might be a matter of size. A critical mass is required for things in the compost heap to start really heating up. A composting guide by the University of Illinois Extension recommends a minimum size of 3 cubic feet.
If, like me, you happen to be an urban gardener with limited space, this minimum requirement might not be an option. But fellow micro-farmers needn't despair: for those constrained by lack of space, cold composting -- also known as the Add-As-You-Go method -- is a good option. This approach can be done on a smaller scale and involves adding materials as they become available and allowing them to decompose gradually, scooping finished compost from the bottom (Note: if you're really strapped for space, you might want to try vermicomposting, also known as worm bins, which are often small enough to fit under the kitchen sink).
Cold composting usually takes significantly longer to achieve desired results than hot composting and can result in smellier conditions. Lower temperatures also mean you have to be more careful about what you add, as weeds, plant diseases, and pests that would be neutralized in a hot compost batch may persist in a cold pile and wreck havoc the following growing season. Still, with patience, proper air and water circulation, occasional turning, and a good balance of browns and greens, the stuff you throw in heap will break down and eventually become the rich, nutrient-loaded compost your garden craves.
Leaves: The Only Thing Worth Composting?
Not long ago I stumbled upon a TEDx Talk titled “Everything You Know About Composting is Wrong.” In this video, celebrated garden columnist Mike McGrath calls the pervasive idea that gardeners should compost their kitchen scraps “the Big Lie of composting.” Mr. McGrath makes the argument that shredded leaves and coffee grounds are the only items composters should concern themselves with. Says McGrath,“Every agricultural study ever done says that two inches of yard waste compost made with this incredible, nutrient-dense energy harnessed by trees through their leaves is all any plant needs to be fed and protected from disease for an entire season.” He goes on to explain that kitchen scraps are virtually useless to the compost heap, saying, “Your kitchen garbage is cold, meaning it has no nitrogen [...] It is only the leaves that become the compost.” The one exception, according to McGrath, is coffee grounds, which add moisture and nitrogen and speed the composting process tremendously.
Since Mr. McGrath has a much longer history of garden expertise than I do, I naturally took his advice at face value and promptly gathered up the leaves I had sitting in my yard since the previous fall, shredded them, and applied them to my garden beds as a mulch. But the claim that my kitchen scraps are of no nutritional value didn't sit right with me. After all, like leaves, these items are plant-based materials that absorbed energy and nutrients during the growing season, so why shouldn't they be able to make some valuable contributions? Moreover, every other source of information about composting I'd ever found identifies leaves, twigs, sawdust, and newspapers, as carbon-rich “brown” materials while the “green” materials that comprise kitchen scraps are an essential source of nitrogen. Now suddenly I was being told that those greens are actually devoid of nitrogen?
I became even more suspicious when McGrath explains to one fan in an article for Gardens Alive, “Kitchen scraps and other ‘wet greens’ mostly just feed the microorganisms that fuel the process.” Having recently read up on the soil food web, I knew that feeding those microorganisms is a big deal, not something so easily dismissed. In fact, increasing microbe populations in the soil is one major benefit of using compost. And really, it's what all organic fertilizers do: feed microbes which in turn feed plants. Whether it's brown or green, the stuff that goes into the compost heap must be decomposed by microorganisms before its nutrients are available to plants. It's a principle that applies as much to dead leaves as it does to banana peels.
Here are some nitty-gritty sciency details about leaf compost. Despite Mr. McGrath's claim to the contrary, there are, in fact, agricultural studies that advise supplementing leaf mulch with additional fertilizers. The main contribution of leaf litter -- and other common “brown” materials used in the garden or compost heap -- comes in the form of carbon, not nitrogen. According to an article by researchers at Rutgers University which examines the effects of applications of municipal leaves (i.e. those leaves we rake to the curb every fall) to various crops, raw leaves have an average carbon-nitrogen ratio (C:N) of 50:1, which is considered a relatively low nitrogen content. A fact sheet by Colorado State University Extension explains how a C:N of 20:1 or higher can result in a nitrogen deficiency in the soil. Both articles recommend supplementing an application of low-nitrogen materials (e.g., leaves) with a nitrogen-rich fertilizer.
According to Jeff Lowenfels and Wayne Lewis, authors of the soil food web bible Teaming with Microbes, the ideal average C:N for successful compost is ranges between 25:1 and 30:1. This doesn't mean that high-carbon materials should be excluded, only that they need to be balanced with high nitrogen materials (if you're confused about which materials are nitrogen-rich “greens” and which are carbon-rich “browns,” check out this handy list by eartheasy.com). When we delve even deeper into the mechanics of the soil food web, we learn that green materials support bacteria populations while brown materials support fungi populations -- and further, that bacterially dominated soils are ideal to support the growth of annual plants while perennial plants prefer fungally dominated soils. In plain English, this means that certain plants -- perennials, trees, shrubs -- will be happier with compost that's got more brown than green, while others -- vegetables, annual flowers -- want compost with more of the green stuff.
McGrath's main premise, that leaves should be treated as compost gold rather than an autumn chore, is not without merit. By all means, treasure those leaves! They are a valuable source of brown materials that can otherwise be difficult for the home composter to come by. But my casual perusal of the web -- with sources ranging from hobbyist blogs to university studies -- found zero support for the claim that kitchen scraps contribute nothing to the compost pile. Nor does personal experience suggest, as Mr. McGrath does, that food waste tossed in the compost heap will be the same, uncomposted food waste three months later.
Is There Such Thing As Too Much Coffee?
There is a lot of conflicting advice out there regarding the use of spent coffee grounds in the garden or compost heap. Because coffee is acidic as a drink, it's long been assumed that the grounds are acidic as well, and therefore potentially dangerous to all but the most acid-loving of plants. New evidence, however, suggests that coffee's acidic element is washed away (into your mug) during brewing, and spent grounds are actually close to neutral in pH. Some sources suggest applying spent coffee grounds directly to the soil, but the recommended quantity and frequency of applications varies widely from one source to another. To complicate things further, some authors raise concerns about the possible impact of caffeine on plants and the tendency of coffee grounds to dry out and repel water. A fact sheet by Oregon State University even contends that, contrary to everything gardeners have been led to believe about coffee grounds, grounds applied directly to the soil can actually deplete nitrogen levels, rather than supplementing them, due to the way nitrogen is used by microorganisms during decomposition.
Composting coffee grounds appears to be safer and less complicated than applying them directly to the garden. In the compost heap, the high nitrogen content of spent coffee grounds (around 2 percent by volume) is a significant asset to the composting process. Once again, suggestions on how much to add vary, but the general consensus seems to be that coffee grounds can safely account for up to 25 to 30 percent of the total mass. Despite their color, coffee grounds should be treated as nitrogen-rich greens (filters, however, are considered browns).
Finally, there is overwhelming anecdotal evidence that earthworms -- those beloved compost companions with magical poop -- are crazy about coffee. Having seen the speed with which the worms in my compost bin grew from nearly indistinguishable slivers into fat, vigorous adults, I'm inclined to believe the hype.
Newsprint, Bleaches, and Salmonella, Oh My!
If you're one of the exactly 37 people left in the country who still subscribes to a daily print newspaper, you may have been excited to learn that newspapers can serve as a valuable brown material in the compost heap; you may have been subsequently disappointed when you were told that the ink used in these newspapers contains toxic chemicals and should be excluded from the heap. Then maybe you heard that the ink used in most newspapers today is soy-based rather than petroleum-based, and therefore biodegradable and perfectly safe. And then, as luck would have it, some naysayer came along to contend that these soy-based inks still contain toxic chemicals and have no place in organic gardening.
The truth is this: soy-based inks do contain trace amounts of toxic compounds, but the levels are low enough that they're not considered a risk, either to soil ecology or human health. This is true of both colored or black-and-white print. Glossy magazines have higher concentrations of unwanted chemicals and are better off relegated to the recycling bin.
Diehard organic gardeners -- those who won't compost scraps from produce that wasn't organically grown -- will probably opt out of using newspaper in the compost heap. But ultimately, there's little evidence to suggest that composted newspaper inks do any damage to the garden. The same, incidentally, is true of bleach found in coffee filters and paper towels, a similarly contentious topic. As an article by TheCompostGardener.com puts it, “Compost organisms are easily up to the task of breaking down any tiny amounts of bleach residue that may be on the filters.” To put that in perspective, whatever residues are present in newspaper inks or coffee filters are more benign than chemicals used in MiracleGro fertilizers, which decimate microbe populations in the soil. Moreover, as Grist.org's Ask Umbra points out, for city dwellers like yours truly, whatever toxins might remain in these inks and bleaches are “a drop in the contamination bucket.”
Eggshells are another somewhat controversial item in the world of composting. Like newspapers and coffee filters, eggshells are a near-universal item on lists of compostable materials. They are lauded as being rich in calcium and acting as a natural remedy for blossom-end rot and slug and snail infestations. Some gardeners complain that eggshells in the compost create smelly conditions, attract animals, and take too long to break down, problems which can be mitigated by crushing eggshells into small pieces or using a food processor to turn them to powder. The real fear surrounding eggshells, however, is the possibility of salmonella contamination. Some growers fear that composting eggshells risks transferring salmonella bacteria to the garden beds where they will be absorbed by produce, eventually sickening unsuspecting humans come harvest time.
The chances of composted eggshells causing illness in humans is very remote. For one thing, hatcheries in the United States are subject to numerous inspections and safe handling standards that help reduce the likelihood that eggs will contain salmonella at all. Moreover, as Food Safety News reported in 2013, studies have found very little support for the idea that produce can become contaminated by absorbing pathogens via root uptake -- so on the off-chance that you do toss in some contaminated eggshells in the garden, it's unlikely that those salmonella bacteria will somehow infect your tomatoes the following season.
If all else fails, high temperatures in a hot compost heap make pathogens like salmonella a non-issue. If you're cold composting and the idea of salmonella contamination still makes you uneasy, rinsing the shells thoroughly in warm water should remove any lingering bacteria. Alternatively, you can try heating shells in the oven for around 20 minutes -- this will also reduce any egg-related odors and make the shells easier to crush.
The plethora of advice out there on the “proper” way to go about composting can be paralyzing for the uninitiated, or for anyone like me who wants to get things right on the first try. But really, composting isn't as complicated as it's made out to be. Yes, certain elements -- such as adequate air and water circulation -- are crucial. And yes, certain practices can result in compost that's smellier or slower to break down or more attractive to unwanted critters. But ultimately, organic stuff rots. If it didn't, the world would be buried in organic matter. So don't let the confusion get to you: throw that stuff into a pile and whip up a batch of free, fantastic fertilizer.
COMPOSTING CHAOS: SORTING THROUGH THE MYTHS AND MISCONCEPTIONS by UrbanSculpt Staff Writer Leslie McIntyre is licensed under a Creative Commons Attribution 4.0 International License.
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