If your compost bin has cooled down, there are several steps you can take to help raise the temperature by making conditions in the bin ideal for heat-generating micro-organisms.
- Aerate
The aerobic bacteria that get compost hot need oxygen to breathe. Regular aeration – about twice a week – reinvigorates microbial activity.
In the immediate aftermath of turning there will be a dip in temperature but ultimately it will result in a higher bin temperature for a longer time. After a couple of days, you should notice things are heating back up. Aerating the contents will prolong the time that the bin stays at these temperatures. As heat-creating bacteria proliferate they use up more oxygen so regular aeration is needed.
Aeration also helps all the materials to make their way to the heat in the middle and to decompose at an even rate, as well as distributing water and nutrients to all areas. Without air, the contents will turn anaerobic – the breakdown process will slow down and the contents start to smell unpleasant.
The aerator stick that comes with the Green Johanna has retractable blades which release after you have pushed the stick into the compost, helping to stir the materials.
If adding food waste in home compostable bags, use the aerator stick to split the bags open in several places to ensure microbes can easily access the waste. Tearing the bag up means it will also decompose faster.
Tip – For deeper aeration, a manure fork is lighter and easier to handle than a garden fork.
2. Check moisture
The heat a compost pile generates can lead to dry spots. Stirring enables you to check how dry the compost is inside. As you aerate you can check moisture levels to ensure the compost isn’t dry, especially if the bin is in a sunny spot. Bacteria need moisture to move around the compost. But if there’s too much moisture, air will be forced out of the bin. With experience you can tell by looking.
The ideal moisture content is around 50 per cent. You can check by using a moisture meter or by doing the squeeze test – wearing gloves, grab handfuls of the bin’s contents and squeeze. Only one or two drops of liquid should appear. The ideal consistency is like a wrung-out bath sponge.
If compost is too wet there is less air for the microbes – if this is the case, add carbon materials and aerate. If it’s too dry, add water from a small watering can with a fine rose spray and aerate so moisture is spread through the bin.
The presence of a lot of ants is a sign the compost is too dry; a lot of slugs means it’s too wet.
TIP – If you need to water compost that is dry, use rainwater from a water butt if you can – it’s naturally soft and free from minerals and salts and treatment chemicals. This also saves on using tap water. If compost is only slightly dry, add wet materials such as coffee grounds and fresh grass in small amounts.
3. Chop or shred
Items should ideally be 2 to 5cms.Smaller items provide a larger surface area for more microbes to work on. The more micro-organisms at work means faster, hotter composting of waste.
TIP: If you have a lot of dead leaves throw them in an empty dustbin or compost bin and whizz them up with a strimmer. Or you can spread them over your lawn and mow, so you shred the leaves as well as grass, giving you a useful mix of nitrogen and carbon.
4. Provide air pockets
Carbon-rich materials are often called bulking agent. They add structure and substance to the compost; high nitrogen materials can compost very quickly down to very little. They also trap air through the compost, getting oxygen to the aerobic microbes, and absorb excess moisture, which makes them essential to add alongside foods with a high moisture content such as cooked foods and fruit waste.
Cardboard can be torn into strips or squares. Look out for corrugated cardboard in packaging; the holes are great for adding air pockets. Other good sources of air pockets are egg cartons and the tubes from toilet rolls, which can be added whole.
TIP: Wood chips (from untreated wood) are great for adding airflow, providing food for fungi and absorbing moisture from wet foods.
5. Store carbon
It’s well worth the effort to prepare plenty of bulking material ahead of time. If not, you might be tempted to skimp on the carbon that’s needed in the bin if you don’t have it ready to hand.
In home composting, food waste is usually plentiful (providing nitrogen) but carbon takes a bit more preparation. Prepare it in advance and keep it near the compost bin in tied bags or lidded containers – an old dustbin, empty composter, or lidded plastic tubs – so it’s ready when needed.
Doing this in autumn when you have lots of garden waste will keep you going through winter. Don’t let it get wet or it will start to break down.
Many people bag up and store dead leaves in autumn so that they’re readily available throughout the year. Then when you add food waste or grass cuttings to the bin, you can add your carbon at the same time.
Some of our customers get into the habit of having cardboard tearing sessions while watching TV (don’t knock it till you try it!), or they get the kids involved as a family activity, introducing them to the basics of composting.
Always cover fresh waste with a layer of carbon to prevent smells that could attract pests.
TIP: Cardboard is easier to tear into strips when wet.
6. Add soil
A quick way to add more beneficial microbes is to add a bucketful of soil or mature compost. A single teaspoon of soil can contain up to 100 million bacteria and 400 – 800 feet of fungal threads.
TIP: A layer of soil added to the top of the contents of a full bin that’s going to be left to mature will reduce heat loss and conserve water.
7. Try Bokashi
The fermented contents of a Bokashi bin turn into pre-compost – added to a compost bin this acts as an accelerator and speed up decomposition.
Great Green System carried out trials using the contents of a Maze Bokashi Bin that had been left to ferment for three weeks and were then added to a Green Johanna. Temperatures in the Johanna rapidly increased over a few days from around 36 degrees to 66 degrees Celsius (see photos).
Pre-Bokashi – compost temperature at about 36 degrees Celsius.
The fermented contents of a Bokashi bin are added.
Post-Bokashi – compost temperature is raised to about 66 degrees Celsius.
8. Add DIY accelerators
Nitrogen-rich materials that provide a useful boost to the composting process include chicken manure, bird feathers and grass clippings.
Fresh grass will quickly heat up the compost and decompose rapidly, providing ample fuel for microbial activity, but too much will clump and turn slimy so it needs to be added in thin layers.
Other accelerators include nettles or comfrey leaves, fresh or wilted, laid in a thin layer.
9. Ventilation
With a Green Johanna, if the weather is very cold, limit ventilation through the lid’s ventilation system – twist the lid towards the minimum setting to keep heat in the bin.
10. Fit the jacket
Add the Green Johanna’s Insulating Jacket – this provides insulation to retain heat but is easily removed if the compost temperature is getting too high (above 70 degrees Celsius).
The jacket is designed to fit snugly so that cold air can’t circulate round the bin. Follow the instructions so the vents in the base are left exposed and the top jacket sections overlap the one underneath by a few centimetres. This ensures that the vents at the top and bottom of the Johanna are kept free so the ventilation system can work efficiently.
TIP: In autumn and winter ensure the vents at the bottom do not get covered by leaves or snow.
