How to compost in a cardboard box at home

There’s a smell emanating from my kitchen.

The days are marching toward Tokyo’s unrelenting, mold-inducing summer, but I’m not concerned: This odor is earthy, rich and fragrant.

I’m making compost in a cardboard box, a method that’s become popular in Japan over the past decade. The cardboard box composting system’s draw is that it is both cheap and simple, bad-odor-free and well-suited to small Japanese spaces. I don’t need to buy any special equipment apart from coconut peat and kuntan (rice husk ash), both of which are readily available from gardening centers. Nor do I need a special place to set my box up, though sunlight and ventilation are important for success.

One reason I’m interested in composting is to cut down on food waste that has a tendency to quickly fester and smell during summer.

Rich soil: The author’s composting project just before stirring in the day’s food scraps | JANE KITAGAWA

Cutting down on landfill methane emissions — a potent, smelly greenhouse gas — by producing less garbage is an added perk.

COVID-19, said to be exacerbated by the loss of animal habitat due to climate change, has also been a wake-up call. Despite a plethora of online shopping options in Japan, I’ve long thought about microgardening, and figured a ready supply of compost might be the impetus for me to start.

Although Tokyo-based urban gardening advocate and educator Jon Walsh hasn’t yet tried this composting method, he did give me some general tips.

“The basic rule is if you feel comfortable adding something to your compost, do it! Once you start composting, you’ll be really surprised how much material you are not throwing away,” Walsh says. “Scraps from your salads, fruit and vegetable peels. It’s wonderful. Compared to Disneyland, this is real magic.”

My compost, which I covered in an old IKEA children’s towel, becomes an anthropomorphic pet of sorts. Three weeks in, I’m enjoying the easy rituals of feeding my microbe monster its daily diet of food scraps — fruit and vegetable matter, fish and bones, and tempura oil; meat is the one type of food waste this method can’t process. New food gets added to a funnel I dig in the center of the mix, which keeps the box from decomposing, and the kuntan absorbs moisture, so there aren’t any leaks. I’m still wary of attracting insects, but my grade-schooler, who hasn’t otherwise shown much interest, likely wouldn’t mind.

I learn the hard way that I need to chop up my scraps into small pieces — a corn husk I mistakenly add must get picked out, and two overly large kabocha chunks stubbornly refuse to decompose — to generate the heat that kick-starts the composting process and helps kill off any disease-causing organisms. This is where my manual food processor comes in handy.

“Heat drives the bacterial activity, so the hotter the temperatures get, the faster the bacteria work to break down the compost material,” says Walsh, adding that I should check and stir the compost on a daily basis.

He also urges me to begin planning my microgardening journey. As I keep generating compost, I’ll certainly need an outlet for it.

But Walsh’s best advice is the most simple. It’s also failproof: “Just try it and see what works.”

Cardboard box composting

Materials:

1 large cardboard box

Spare corrugated cardboard for reinforcing the box floor

Duct or masking tape

Coco peat (coconut ash)

Kuntan (rice husk ash)

Small hand shovel or scoop to stir the compost

Base or stool for the box to sit on

An old T-shirt, towel or cloth to cover the box

Method:

• Tape and secure the bottom and sides of your box against moisture and unwanted insects
• Line your box floor with corrugated cardboard. Place the box on a raised ledge.
• Add coco peat and kuntan to the box until it’s about ⅔ to ¾ full. Make sure the coco peat to kuntan is a 3-to-2 ratio.
• Stir the mixture using your shovel.
• Dig a hole in the center of the mixture. Add up to 500 grams of food scraps per day into the hole and then cover with topsoil.
• Close and cover your box.
• Repeat steps 4 to 6 daily. The compost should be ready in approximately three to four weeks

(Source: JT)