Saving Waste Like Money: Meeting Microbes in the Compost

Then there is the dark, vital organic matter that makes up the heart of the soil. It comprises hundreds of millions of organic molecules, each possessing its own hue and ability to absorb and reflect light. When these differently coloured molecules mix together, no light is reflected back, which is why the mixture ultimately appears black. Far from being merely the material foundation for life, these organic compounds, when bound with inorganic soil particles, create a stable network of pores capable of holding both moisture and oxygen beneath the surface.To improve the soil, one must start by increasing its organic content.

With this small patch of barren earth in the yard, I finally had a compelling reason to take composting seriously.

I. Starting with everyday household waste

For composting, I’ve collected coffee grounds and simply piled them up at home. I’ve built compost bins in the fields with the non collective, and once, I even went out in the middle of the night to scoop up a large bag of leaves a street cleaner had swept to the roadside, tipping them into the bin.

Over the past two years, during brief stays in other places, I’ve taken part in various community composting projects. From traditional farmyard manure piled with animal droppings in villages, to professional tumbling composters on urban balconies, and to composting at different scales and with diverse materials in eco-villages and farms, I’ve encountered and learned from a wide array of methods.

Now, I’m starting with the everyday rhythms of my own home.

Since I began composting, I’ve been hoarding the organic ‘waste’ from my home with the same careful diligence as if I were saving money. Every kitchen scrap, every leftover meal, every piece of fruit gifted to me that begins to turn before I can finish it… I used to feel a pang of guilt and uncertainty when faced with such surplus. Now I treat it all as treasure, knowing that in the end, it will all become something precious for the soil.

At home, I use Bokashi composting: I add kitchen scraps daily and cover them with a layer of EM microbial powder. (Note: EM refers to Effective Microorganisms, an active culture typically formulated from a blend of Bacillus, photosynthetic bacteria, lactic acid bacteria, yeasts, and actinomycetes, combined with organic carriers such as rice bran or fishmeal. It works by suppressing harmful microbes, particularly pathogens and spoilage bacteria.)

My trusty composting companion is a well-worn pair of heavy-duty kitchen shears. While prepping vegetables, I make a habit of snipping scraps into smaller pieces before dropping them into my daily Bokashi bucket. I also keep a separate bin for used napkins. The end result? My home is dotted with various makeshift containers for ‘waste’ – a tub for coffee grounds, a mug for tea leaves, peanut shells waiting to be blitzed in the food processor. I set aside coffee grounds still wrapped in their pour-over filter papers, laying them out on the balcony to dry; I keep them out of the Bokashi bucket simply because they take up too much space. This approach to composting might seem a touch meticulous, but much like cooking, there’s no single right way or definitive failure. Everyone develops their own rhythm.

During the peak of summer, that 15-litre bucket at home fills up remarkably fast. The leachate needs to be drained daily; it’s not uncommon for a single watermelon to yield a litre or two. Once the Bokashi bucket reaches capacity, I pop over to a local café to collect a couple of bags of used coffee grounds. I lug them back to the small courtyard of my studio and layer them into an insulated box for hot composting.

My hot composting bin is a converted second-hand food-grade insulated box with a capacity of roughly 60 litres. I started my first batch on 10 May, and over the past ten months, I’ve begun a seventh. I keep detailed records of temperature fluctuations and turning routines for every batch. Where I initially struggled to nail down the conditions needed to raise the temperature, I’ve now grown fairly adept at it.

Hot composting traditionally emphasises the carbon-to-nitrogen ratio. Yet my mix usually boils down to roughly equal parts coffee grounds and my Bokashi kitchen scraps, topped off with a bag of shredded paper towels – no heavy feeders like fish offal. When you get the moisture and aeration right, the carbon-to-nitrogen ratio tends to become the least of your worries.

More importantly, I’ve begun to view composting through the eyes of microbes, considering what constitutes easily digestible food for them and what conditions offer a comfortable habitat.

Within a hot compost pile, a bustling array of bacteria and fungi thrive. Some operate at moderate temperatures (25–45°C), while others prefer the heat (45–70°C). Among the mesophiles, you’ll find varieties that sprout fine, white, hair-like mycelium, and thermophilic actinomycetes appear as tiny, speckled patches of grey-white. Yet the vast majority of these microbes remain invisible to the naked eye. They feverishly break down the food residues that our own bodies could not process. In this act of digestion, we and the microbes finally meet.

At the very least, the vegetables I’ve sown, nourished by this compost, are thriving. My primary aim for now remains to cycle the organic waste from my daily life back into the soil.

Had I not started composting in my everyday life, I doubt I would have truly grasped that making compost, much like keeping a jar of kimchi or a sourdough starter, demands daily, sustained attention. Sorting paper towels into their own pile, snipping kitchen scraps as I go—these manual routines have become second nature when I’m at home. Some might see it as a chore, but I find joy in it. These habits have also spared me the hassle of taking the bins out; now, the actual rubbish bin in the house goes weeks without filling up.

It was also because I began growing vegetables a few years ago that I started reading into care ethics and ecofeminism. Academic discourse uses theory to explain the world, while the body navigates life through concrete action. When Tronto and Fisher wrote on care ethics in 1990, they defined care as “a species activity that includes everything we do to maintain, sustain, and repair our ‘world’ so that we can live in it as well as possible. This world encompasses our bodies, ourselves, and our environment, and we strive to weave all of it into a complex, life-sustaining network.” In the process of caring, we invest emotion and form affective bonds with those we look after. Yet care is often dismissed as reproductive labour within the domestic sphere rather than productive work, and thus goes unvalued.

And tending the soil, however, is the most fundamental form of production. In the chapter “Soil’s Time” from *Matters of Care*, Bellacasa writes: “Learning about the life within the soil through looking and touching also reveals how intimacy and care forge a connection with the soil’s dark, otherworldly realm.” Composting is no different. Hands immersed in humus, intimately touching and turning the mix—it is both a way of breaking down leftovers and of producing nourishment for the earth.

Maintaining a hot compost pile is no easy task. In summer, pouring out fermenting, sour-smelling bokashi compost in 40°C heat and mixing it thoroughly by hand with coffee grounds is hardly a task everyone would be keen to tackle.

At first, I found it a bit daunting to begin, but after spending time with the process, I gradually grew accustomed to the smell of the compost. I do not find the fermentation odour of Bokashi compost unpleasant. Once the peak heat passes and the material transforms, the scent that emerges is complex and richly fertile, carrying a subtle freshness that evokes the solid, warm feel of earth.

Once the heat of the compost has subsided slightly, I turn it with bare hands, crushing any larger chunks as I go. By this stage, most of the food waste has already broken down. A few items, such as corn cobs or pomelo skins, may still retain their shape, but they can be easily crumbled or torn apart by hand. This is hardly a necessary step; I simply enjoy the way the material feels under my fingers.

After turning the pile, my hands retain the scent of the compost, dark organic matter lodges in my nails, and my clothes bear its marks. Through this process, I have gradually come to understand the habits of thermophilic microorganisms. There is no fixed ratio to follow; I must simply monitor the temperature and moisture regularly, turn the pile, and adjust as needed. Perhaps because I turn the pile so frequently, working alongside the microbes to generate that heat, my hands have gradually developed an instinct for the conditions required to sustain it. It is a subtle sensitivity, akin to the early stages of mastering a craft. In this intimate relationship of care, the microorganisms within the compost are also changing and shaping my body.

A while back, I took a box of compost to an exhibition by the non collective. The kitchen scraps I had been saving at home had by then transformed into a loose, sweet-smelling humus. We spread it across the floor of the klee klee & friends shop at Shanghai’s Parkside, inviting visitors to turn it over by hand and feel, through touch, the compost broken down by microorganisms. Over the course of the exhibition, we also ran a composting workshop, guiding participants through the process of making hot compost.

Another friend, designer Houzi, who lives nearby, picked up a bucket too. We soon began swapping kitchen scraps for fertiliser. Not long ago, when I started a fresh batch, she brought her home Bokashi bucket over. Before heading out, I had her take a bag of fully decomposed compost to fertilise the blueberries she grows in pots at home.

On this occasion, however, the divider in Houzi’s bucket had gone wrong, causing poor drainage. The fermented result was a sticky, foul-smelling sludge of solids and liquids.

Composting can be like that. If the nutrient-rich liquid isn’t drained in time, it produces a foul odour that turns many people off. But it hardly counts as a failure; these organic materials will ultimately become nutrients for the soil anyway. I mixed what she’d brought with coffee grounds, paper towels, and wood shavings, adjusted the moisture to the right level, and added it all to the compost bin. A few days later, the temperature inside the bin climbed to 65°C, and the smell shifted to the earthy scent of active decomposition.

Another friend in Shanghai has recently moved to a studio with a courtyard, and I managed to win her over to composting too. Of the two rose bushes in her yard, the one regularly fed with Bokashi leachate is clearly growing and flowering much more vigorously.

Composting has forged a physical connection between eating and growing. It feels like a highly tangible bodily practice, even on the extremely limited patch of urban earth we have. This practice of composting has also made me reconsider the origins of our food, the soil beneath it, and the process of its production. For those of us living in the city, how can we eat better, and how can we grow better?

In the studio courtyard, dark compost was worked into the reddish-brown clay. Slowly, the soil began to loosen, its colour shifted, and moisture no longer drained away so quickly. Last summer, luffa, okra, chillies, and dragon fruit thrived in the ground (the tomatoes, however, failed to survive Hangzhou’s scorching heat), and cauliflower and peas were sown in autumn.

I dilute the Bokashi leachate with water before applying it, while the fully decomposed output from hot composting is scattered directly on the surface as fertiliser. When sowing peas in autumn, I noticed that areas where compost had been mixed in during the summer loosened with just a light dig, whereas spots without it remained as hard as rammed earth.

At this moment, with a large bin of sieved compost at my side, I feel incredibly wealthy, my heart brimming with anticipation for spring.

[2] Tronto, Joan C. 1998. “An Ethic of Care.” Generations: Journal of the American Society on Aging, vol. 22, no. 3, pp. 15–20.

[3] Bellacasa, María Puig. 2017. Matters of Care: Speculative Ethics in More than Human Worlds. Minneapolis: University of Minnesota Press.