Bokashi composting: A beginners guide to slimming down your black bin waste

“Can I put my grandchildren’s nappies on my heap?”

One of my favourite talks to give to gardening clubs and groups* is on bokashi composting. Mostly this is because there’s always some curveball of a question at the end, like the one above, which blows away all your preconceptions about people’s understanding of the subject. Well yes, “night soil” (a euphemistic term for human faeces) has been a component of home composting in the past, and still is in some parts of the world, particularly China, but this is not recommended for the home gardener, unless you follow a specific regime as laid out in the bible on the subject, The Humanure Handbook. 

But, as rubbish collections across the country begin to switch from weekly to fortnightly as a cost-cutting measure, it’s easy to see why people are desperate to find any way possible to reduce the load on their black bin. The average UK family bins 13lbs of food (that’s nearly 5.9kg) every week. It’s doubtless true that some of this waste can be eliminated by smarter shopping, using up leftovers and being more aware of the difference between sell by and use by dates, but composting also has a big role to play in slimming down our black sacks. 

The range of foods we can put in our garden compost bins is traditionally fairly narrow: meat, dairy and cooked foods are out, because they attract rodents; some people don’t like to add citrus or onions for fear worms won’t like it; tea bags aren’t put in because people find they don’t degrade fully due to the presence of plastic (I use loose leaf tea instead…)

There’s no single answer to this range of issues, but one of solution that can help is bokashi composting (particularly if your council, like mine, doesn’t offer a food waste collection service). Mention this to the audiences at most gardening clubs and you’ll get blank looks, but this is a technique that is gaining ground in the UK. The principle is this: food waste (meat, dairy, and cooked food included) are fermented using Effective Microorganisms or EMs, beneficial microorganisms that are delivered via an inoculated bran that you sprinkle over the surface of the food as you pack it into a lidded bucket. Unlike regular composting, the process is anaerobic, so you want to exclude as much air as possible by squishing the waste down as much as possible when topping up, and keep the lid on tightly. 

Once one bucket is filled, you put it to one side and start filling the second (they are generally sold in pairs). The only task to do in between times is draining off the leachate produced by the fermenting food, which you can draw off from the tap at the bottom and either pour into drains to help keep them clear and smell-free, or use heavily diluted in water as plant food. (Alys Fowler told me about one bokashi guru who was so confident in the quality of his process that he’d drink the bokashi liquid, but I wouldn’t recommend this). 

You know if you’ve been successful, because after two weeks or so, the food in the first bucket will be covered in white mould, and will be ready for emptying. It may not look that much different, and it certainly won’t look like the final product from your regular compost bin, but it’s ready for the next stage of the process. It should smell more pickled than rotten. I have really tested this theory with some batches, putting in everything from raw fish skins to the rinds of stinky cheeses, and even they haven’t made a stink. If the mould is green, this is a good indication that things have gone wrong and you need to start again – too much air getting in, or not adding enough bokashi bran are the usual reasons for failure.

This is where things get a little tricky. Fermented waste can be dug into the ground, or added to compost heaps or wormeries. In my experience it’s best not to add really thick layers of bokashi waste to bins or worm trays, and certainly don’t dump a whole bin’s worth in at one go: I don’t know whether it’s the lack of air, the acidity or something else, but it seems to break down better when added in small clumps. And if you have a dog, take care if digging into the soil: this stuff is manna to my lurcher, and he has been known to dig the stuff up and eat it. It didn’t do him any harm, but if you have composted cooked chicken bones, say, it may result in an expensive visit to the vet. 

My other way of dealing with bokashi waste is my own invention, and is useful if you have run out of room in your composter and/or wormeries, or have the aforementioned issue with greedy dogs. I take a large container – old kitchen bin, builder’s bucket or similar – and a load of “spent” compost from grow bags or containers, and add this in layers, sandwiching the bokashi waste in between until I reach the top. This gets covered over so the dog can’t get in, and left behind the shed for a few weeks or even months. By the time I am ready to do some container planting, or mulch my veg beds, the “spent” compost will be revitalised and the bokashi will be fully incorporated.

One final tip: the biggest flaw to bokashi composting kit (and water butts, and wormeries) is the tap at the bottom. If you are not extremely careful – and to be honest, even if you are – you often find that the tap stops turning or starts leaking. After several extensive searches for a cure, I think I have found it, thanks to a suggestion from fellow blogger Andrew O’Brien. PTFE tape (aka teflon tape in some parts of the world – available from all good hardware stores) is used by plumbers to make a waterproof seal threads on pipes  – just apply some to the threads on the tap mechanism and you’ll fix the leak problem. There’s a useful YouTube video showing how to apply it properly (including why to wind it on clockwise): worth watching as it’s rather fiddly!

I’d love to hear whether you’ve tried bokashi composting, and whether you have any top bokashi tips. Add your comments below.

*If you’re interested in booking me to do a talk for your gardening club, let me know via the contact page.