Can I still hot compost through winter?

The Green Johanna is well equipped for winter – it was designed in Sweden to withstand temperatures of -20 degrees C.  

But even so, what are the best ways to keep hot composting through the coldest months?

 It’s good to remember that hot composting is basically a set of techniques that enables you to achieve higher temperatures and faster decomposition than traditional composting methods, usually referred to as cold composting.

The Johanna’s design helps the compost to achieve those higher temperatures thanks to several features. The adjustable ventilation system includes vents in the base plate to allow air to flow upwards into the container.  The twist lock lid also allows the upper vents to be opened or closed depending on conditions.  In the coldest weather when you want to retain heat, turn the ventilation setting to minimum.

The round shape ensures there are no cold corners so heat is spread evenly through the compost, and the tapered design means that compost sinks towards the centre of the unit and not to its sides, allowing air to circulate and oxygenate the compost.

  The enclosed design also helps to retain heat (most garden composters feature an open or loose-fitting base). The container’s walls are thicker than most other composters and at 10kg the Johanna weighs in at 2-3 times the weight of most bins.

Use of the Johanna’s Insulating Jacket also gives you more control over the compost temperature, providing insulation to keep compost warm but removeable if the compost gets too hot (above 70 degrees C) as the composting micro-organisms will then die off and the process will stall. Compost thermometers, which have a long stem to reach down into the compost, are available from garden centres and online.   

  In winter if external temperatures fall lower than 5 degrees C, we recommend that the jacket should be added, even if you are cold composting, to prevent the composting process stalling.

 The jacket is made from foam polyethylene – a lightweight, water-resistant material that is tough but flexible and designed to fit snugly to prevent cold air from circulating round the Johanna. It also helps to provide added protection against rodents. When fitting the jacket, it’s important to ensure that the bottom section does not cover the vents at the sides of the Johanna’s base as these are necessary for airflow.

Using the jacket is a matter of choice – some Johanna owners never use it and still get good results; others keep it on all year round. Last year the GGS team experimented with leaving the jacket on all year following positive feedback from a number of customers who had done this.  Our main finding was that leaving the jacket on, (and using hot composting techniques) raised compost temperatures into the 30-to-60-degrees C range even in the coldest winter periods, as our photos show.

A Great Green Systems Johanna and jacket in January this year when the ground temperature was at zero, below.

But inside the Johanna the compost kept warm at 40 degrees C.

Don’t worry that using the jacket will make the Johanna too hot for worms, as one customer suggested. This is not a problem because worms can easily enter and leave the composter through the small holes in the base plate. At temperatures approaching 30 degrees Celsius they will move where it is cooler, usually the bottom of the bin where the compost is maturing, or they can leave the bin entirely.

As the micro-organisms break down the waste, they generate heat. As the temperature in the compost fluctuates, the types of micro-organisms present also change.

In winter especially, don’t forget your good composting habits:

  • Feed the bin regularly.
  • Balance carbon/nitrogen levels – a ratio of half nitrogen (food waste) to half carbon (autumn leaves, shredded paper, torn cardboard, twigs, branches). Autumn clippings can be stored to add throughout winter.
  • Aerate regularly – use your aerator stick regularly as normal, but also aerate deeper into the pile on a weekly basis with a garden fork or manure fork, which is lighter.
  • Chop items up to increase surface area. This will also make turning the compost much easier.   Use a chipper-shredder for your garden waste if you have one (or hire one).
  • Check moisture levels – if you squeeze handfuls of compost you should only see one or two drops of liquid.  The ideal consistency is like a wrung-out bath sponge.

There are many factors that affect composting outcomes – these can include location, climate, household diet and the user’s level of involvement. We hear many different stories from all over the country in different situations and locations.   

For many people composting is a fascinating subject that can become a hobby.

Adam Johannes – known to his customers and followers as Compost Guy – says he really enjoys the active hands-on involvement of aerating his Johanna. His children join him in his Saturday morning routine of ripping up cardboard so he has a ready supply of carbon content for when he needs it.

Anthea Rossouw, who has been teaching composting using Johannas for decades, both in this country and her native South Africa, says she loves to see people who started out knowing nothing becoming evangelical about their new interest.

A new customer who took up composting recently on retirement admits cheerfully that she has become ‘obsessed’.

In a Garden Organic webinar, a master composter said that while composting slows down in winter, their experience is that the Johanna keeps going. With a bit of love and attention, that’s our experience too.

Let it snow – but carry on composting

 Snow is on the ground at Great Green Systems HQ right now – providing a timely reminder not to leave your little green friend out in the cold. (I’m thinking of your compost bin but perhaps you have other little green friends).

Follow our cold weather tips and keeeep composting! (with apologies to Strictly Come Dancing…)

Green Johanna

  • Check that the vents at the bottom of the Johanna are not blocked by leaves or debris (or snow!) Air is taken in at ground level so keep this area clear so that air can enter freely. The incoming air goes up past the four ventilation plates on the inside of the base plate, past the maturing compost layer up into the decomposing compost where it provides oxygen for the composting micro-organisms.
  • Also check that the Johanna’s Insulating Jacket doesn’t cover the ventilation holes. The jacket should be installed with the two upper sections pulled down so they overlap the section underneath by about 5 cms. Doing this leaves the ventilation holes clear.
  • In freezing weather limit ventilation through the lid’s ventilation system – twist the lid towards the minimum setting (in summer it should be fully open on the maximum setting).
  • The pre-Christmas period is a good time for getting some great carbon sources ready. Ordering presents or appliances online means they might arrive packed in lovely, corrugated cardboard, which is fantastic for adding airflow to the bin.
  • Now you’ll be glad you stored those leaves. Keep them in lidded containers to keep them dry. If you have loads, keep a large composter, such as the Graf Thermo King 900L, specifically for leaf mulch and take some leaves from the top as carbon sources for the Johanna. Dead leaves are great for absorbing moisture in waste with a high water content, such as bokashi bin contents or fruit waste.
  • If you see tree surgeons at work locally, it’s worth asking if you could take some woodchips or they might deliver them to you for free. Wood chips are good for creating airflow and adding plenty of fungi to the bin.
  • Give the bin’s contents a boost by adding bokashi bran, ground coffee granules or a layer of soil or mature compost.  
  • If you’re setting your Johanna up in winter, don’t be tempted to rush and omit the foundation layer of around 15 -20cms of woody garden waste. Some people ask us if they really have to do this, and the answer is yes. From the beginning, it helps to create airflow from the bottom up through the composter as well as adding structure for drainage. Then add two bucketsful of soil or mature compost to add a healthy amount of micro-organisms right from the start.  

Bokashi bins

  • If you’ve kept your bokashi bins fermenting in a shaded spot outside in the summer, move them indoors. Bokashi bins shouldn’t be exposed to extreme temperatures, which might mean micro-organisms overheating or freezing depending on the season.  When the bin is full and needs to be left to ferment for two to three weeks, if you want it out of the way store it in a garage or shed as long as it won’t freeze.  


  • Wormeries should also be placed where they won’t be exposed to extremes of temperatures. Depending on your location, move an outdoors wormery to a sheltered area or if it is to stay outside, cover with a tarpaulin.  Keep worms warm with plenty of bedding and a hessian blanket.

Green Cone

  •  Stock up on accelerator powder – you will need more than usual to boost the process now that there is less sun to provide energy for the solar-powered unit.  
  • Even if you have more food waste than usual over the Christmas period, make sure you never allow food waste to come higher than the Cone’s underground basket. Food waste must never be above ground level inside the Cone itself.

Remember your usual best composting practices, whatever the weather:

  • Regular feeding: Keep adding to the bin to maintain the composting process. The generous 330 litre size of the Green Johanna means the mass of contents acts as an insulating factor.  If your household is small and struggles to add enough content in winter with the lack of gardening clippings, accept food waste from neighbours, as some of our customers do.
  • Chop items up. Smaller items provide a larger surface area for more microbes to work on.  This means higher temperatures and faster breakdown.
  • Ensure a good balance – adding a caddy of food waste (rich in nitrogen) followed by a caddy of carbon-rich materials (dead leaves, shredded paper and cardboard, twigs, branches, woodchips) is a good habit to get into.
  • Check moisture levels – especially if you’ve added a lot of dry autumn leaves (carbon) which could make the mix dry. Composting contents should have a moisture level of around 50 per cent, with the consistency of a wrung-out bath sponge. Add rainwater from a water butt (in a watering can with a fine rose) if the materials are becoming too dry. Don’t just check the top layer, get handfuls from lower down the bin too. Check by using a moisture meter or by doing the squeeze test – wearing gloves, take large handfuls of compost in both hands and squeeze – only a drop or two of liquid should emerge. If there are no drops, the compost is too dry and needs watering.
  • Regular aeration – it’s important to keep adding air to the bin as the aerobic microbes breaking down the waste need air to breathe. Without air, the contents will turn anaerobic and start to smell.   

Don’t forget to pay attention – getting into the habit of knowing what’s happening in the bin enables you to take corrective measures to prevent problems. 

Spare Parts