I've been running a Green Johanna for years, with the insulating jacket on it through the coldest months. It is the bin I point people at when they want to compost the food that most bins can't handle.
This is everything I know about getting one working properly. Setup, feeding, the jacket, and the mistakes that stop it heating up.
What the Green Johanna actually is
It is a hot composter. It holds heat in rather than letting it escape, so the material inside breaks down far faster than in an ordinary bin.
A standard plastic dalek bin sits at under 20°C and takes a year or more. A Green Johanna that is fed properly gets to 40 to 60°C and gives you compost in four to six months.
The part that matters most to people is what goes in it. Cooked food, meat, fish and dairy all go in, mixed with garden waste. Ordinary bins can't take any of that safely.
It was designed in Sweden and is made in the UK.
Who it suits
It is built for a household of around five people with a garden. That is the sweet spot.
It suits you if you are putting cooked leftovers in the general bin and feel bad about it. It suits you if you gave up on composting because of rats, or because nothing ever happened. It suits you if you want a decent volume of compost back at the end.
I will be straight about who it does not suit. If you have no garden, or only a paved yard, this is the wrong bin. If you produce very little waste, it will struggle to get going, because a 330 litre bin needs a reasonable amount of material in it to hold heat. And if you want something you fill and forget, this is not it. The Johanna needs feeding properly and a stir every time you use it. Not much work, but it is not nothing.
If you have no garden at all and just want food waste to disappear, look at a Green Cone instead. It buries into the ground and breaks food down into the soil. You get no compost back from it, and it takes no garden waste, but it is far less work.
What makes it different
The ventilation. Air is drawn in through vents in the base plate, rises up through the material and leaves through adjustable vents in the lid. It is a patented airflow system and the effect is like a chimney. That moving air feeds the bacteria that need oxygen, and those are the ones that don't smell. Compost that has run out of air is what smells.
The base plate. The holes in it are 4.5mm across. Big enough for worms and drainage, small enough to deter rats and mice. I want to be careful with this one, because no compost bin anywhere is genuinely rat-proof and I won't tell you otherwise. What the Johanna does is remove the easy way in, which is more than most bins manage. It only works if the bin is sitting flat on the ground with no gap under the rim, and if you keep the base hatches screwed shut when you are not harvesting. If you have serious rat pressure where you live, put paving slabs or wire mesh underneath as well.
The cone shape. The bin tapers inwards, so as material breaks down it sinks towards the middle rather than clinging to the sides. The middle is the hottest part. No cold corners where things sit undigested.
The modular build. It is four separate rings that screw together. If one gets damaged you replace that ring rather than the whole bin, which is a large part of why these last ten years and more.
Green Johanna specifications
- Capacity: 330 litres
- Height: around 94cm, and you want roughly a metre square of space so you can get around it
- Material: 100 per cent recycled plastic, UV-stabilised so it doesn't go brittle in the sun
- Guarantee: five years
- Designed in Sweden, made in the UK
- Aerator stick included
Setting it up
When to start
Spring or summer if you can. A bin started in warm weather gets going in a couple of weeks. One started in December will sit there doing very little until things warm up, and you will assume you have done something wrong.
Where to put it
Somewhere shady and sheltered. Not full sun, which dries the contents out, and not somewhere exposed and windy, which cools it down.
It needs to sit on soil or grass. Liquid needs to drain away and worms need to get up through the base plate. You can put it on a hard surface if you allow for drainage, but the liquid that comes out will stain stone or decking, and you lose the worms.
Pick the spot carefully, because once the bin is full you are not moving it. Not without emptying it first.
Assembly
Four modular rings marked A to D that screw together, plus the base plate. Around thirty to forty-five minutes with a Phillips screwdriver. The letters and alignment arrows are printed large, so line them up as you go.
The base layer, which most people skip
Before any food goes in, put down 10 to 20cm of coarse material at the very bottom. Twigs, small branches, woodchip.
This is the step people miss and it is the most common reason a new Johanna fails. Without it the base vents block, air stops moving, the bin goes airless and it starts to stink. Then people think the bin is faulty when it is just suffocating.
What to put in a Green Johanna
You need a mix of greens and browns. Greens are the wet, nitrogen-rich things. Browns are the dry, carbon-rich things.
Greens: vegetable peelings, cooked food, cooked meat and fish, dairy, tea and coffee grounds, grass clippings.
Browns: shredded paper, cardboard with the tape off, chopped twigs, dry leaves, woodchip.
The rule that matters more than any ratio is this. Every time you put food in, cover it with a layer of browns. That soaks up the moisture and caps the smell. Over time you are aiming for roughly equal amounts of the two.
Then stir the top with the aerator stick. Every time, not now and then. Once a month, give it a deeper stir.
The thing that catches everyone out is running out of browns. Food waste is constant, browns are seasonal. Stockpile autumn leaves in sacks, keep shredded paper and cardboard next to the bin, and keep a bag of woodchip handy. I have written about where to find them in my guide to greens and browns.
What to leave out
Bones are best kept out. They won't break down, so you end up picking them back out of the finished compost. Raw meat and raw fish are worth avoiding too. Large amounts of cooking oil or fat, nut shells, seafood shells like oyster and crab, and avocado stones will all survive a full cycle and come out the other end looking much as they went in.
Never add dog or cat mess, or used cat litter. Bedding from vegetarian pets like rabbits and guinea pigs is fine.
The Green Johanna Winter Jacket
The jacket is foam polyethylene and comes in four pieces, three around the body and one for the lid. It keeps the core warm so composting carries on through the cold instead of stalling.
Fit it when average outdoor temperatures are consistently below 5°C. In most of the UK that is November through to March.
The important bit is knowing when to take it off. If the inside of the bin gets above about 70°C, it becomes too hot for the worms and microbes doing your composting to survive. So the trigger is temperature, not the calendar. If you garden somewhere cold, you may well leave the jacket on for most of the year without any trouble. If you are somewhere warmer, or the bin is running very hot in July, take it off.
A compost thermometer is genuinely worth the money here. It turns guesswork into a number.
Mine is a faff to fit. I am not going to pretend otherwise. But from November onwards it is the difference between a bin that works and a bin that sits frozen until spring.
You can buy the jacket on its own, or as a bundle with the bin if you are buying both.
The first year is slower
Four to six months is what a running bin does. A brand new one takes longer, usually six to eight months, because the microbial life is still establishing.
This catches people out and it is worth saying plainly. If you are three months in and it is not finished, nothing is wrong.
Getting the compost out
There are two sliding hatches at the base. You harvest from the bottom while carrying on feeding the top.
Being honest about this bit: the hatches are small and digging finished compost out through them is awkward work. If you want to empty a lot at once, it is easier to unscrew the top rings and lift them off to get at the pile properly.
What comes out is a dark, crumbly soil improver. Sieve it if you want it fine, and expect to pick out the odd eggshell or bit of nut shell. Spread it on beds and borders, dig it into vegetable ground, or mix it with soil for containers.
Green Johanna troubleshooting
It smells of ammonia
Too much nitrogen. You have added a lot of food or grass without enough browns. Add shredded paper, cardboard or woodchip and mix it through properly.
It smells rotten, like sewage
Different problem. The contents have compacted and run out of air. Get the stick or a fork in and open it up, then add coarse browns like woodchip and twigs to hold the structure open.
Nothing is happening and the bin is cold
Three things to check, in order.
Is it dry? Squeeze a handful. It should feel like a wrung-out sponge. If it crumbles, add water.
Is it all browns? A bin full of dry leaves and twigs has nothing for the microbes to eat. Add food waste or grass clippings.
Is it just cold outside? Below 5°C everything slows. That is what the jacket is for.
Flies
Fresh food is sitting exposed on the surface. Always finish with a layer of browns, soil or finished compost to cap it, and check the lid is closed properly.
Ants
Ants mean it is too dry. Add water and mix.
Something is getting in
Check the base plate is fitted properly and the bin is sitting flat. Uneven ground leaves a gap under the rim, which is the way in. Keep the sliding hatches screwed shut. A slab or some wire mesh underneath adds another layer if you need it.
The hatches keep dropping open
Usually a sign the bin is overfull at the bottom. Harvest some out and screw them shut.
Common questions
Is the aerator stick any good?
It does the job, but it is plastic and it can be hard work pushing it into dense material. Plenty of people, me included, end up using a metal aerator or a garden fork instead. Handle it gently.
Do I need a compost accelerator?
Not if your mix is right. Bokashi is the one genuinely worth knowing about. Pre-treating food waste in a Bokashi bin part-ferments it, so it breaks down quicker once it reaches the Johanna and can give the bin a real lift. If you are already running a Bokashi bin indoors, the Johanna is the natural place for the output.
Can I use compostable bags?
Only ones marked home compostable, never ordinary plastic. Rip them open with the stick as you put them in, or they sit there as sealed parcels and block the airflow.
What if a section gets damaged?
Replacement rings are available, so you swap the damaged section rather than buying a whole new bin.
How does it compare to a HOTBIN?
The HOTBIN runs hotter and faster, 30 to 90 days rather than four to six months, and it handles bones better because of the temperatures it holds. It also needs woodchip bulking agent every time you feed it, which is a running cost. The Johanna is bigger, more forgiving if you are not precise, and cheaper to run. If you want speed, HOTBIN. If you want capacity and low fuss, Johanna. I run both.
Further reading
- Green Johanna 330L Hot Composter
- Green Johanna and Winter Jacket bundle
- Greens and browns: a proper guide for hot composters
- What to do with autumn leaves in your garden
- All hot composters
I'm Adam, the founder of Compost Guy. I'm passionate about empowering people to embrace composting! Whether you're a seasoned composter or just starting your journey, I'm here to help.
