Best ways to raise compost temperature

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.    

  1. 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.

An image of a man mixing composter in a green johanna with the aerator stick

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.

Benefits of the Green Johanna’s jacket

  As the temperature outside plummets so the compost in your bin might cool down, but by maintaining good composting techniques you can keep your compost ‘cooking’ even in the coldest winter periods.

In the case of the Green Johanna, adding the insulating jacket also helps.

The Johanna pictured below in January in Leeds kept its compost warm at 40 degrees Celsius while the ground temperature was at zero.

This particular Johanna received all food waste from a family of four, rising to 10 people over the Christmas period. Carbon sources include stored shredded leaves from several trees in the vicinity, as well as Christmas paper waste such as cardboard packaging, compostable wrapping paper and Christmas cards.

The Great Green Systems team tend to keep the jackets on our Green Johannas for most of the year, not just in winter, as we’re based in the chilly north of England.      

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.

 The jacket is made from foamed 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’s made for Great Green Systems by a specialist foam manufacturer in Northamptonshire.

When fitting the jacket, it’s important to ensure that the bottom section doesn’t cover the vents at the sides of the Johanna’s base as these are necessary for airflow.  

The jacket should be installed with the two upper sections pulled down so they overlap the section underneath by about 5 cm. Doing this means the ventilation holes are left clear.

Green Johanna wearing the Insulating Jacket

 Also check throughout autumn and winter 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 jacket can easily be removed if the compost gets too hot (above 70 degrees C) in warm weather. Compost thermometers, which have a stem to reach down into the compost, are a useful aid.    

  • TIP: Give the bin’s contents a boost by adding beneficial bacteria in bokashi bran or a layer of soil or mature compost. You can also add coffee grounds or chicken manure to add a hit of nitrogen to your mix.  

Johanna planner for winter:

  • In freezing weather limit ventilation through the Green Johanna lid’s ventilation system – twist the lid towards the minimum setting.
  • Wood chips are a great addition, creating airflow and adding plenty of fungi to the bin.
  • Keep adding to the bin – ideally about three times a week – to maintain the composting process. The Johanna’s generous 330 litre capacity means the compost mass acts as an insulating factor. 
  • Chop items up. Smaller items provide a larger surface area for more microbes to work on. 
  • Aerate regularly – about twice a week – to ensure the aerobic microbes breaking down the waste get enough air.  Without air, the contents will turn anaerobic and start to smell.   
  • Check moisture levels – by doing the squeeze test; grab handfuls of the bin’s contents and squeeze. One or two drops of liquid should appear. The ideal consistency is like a wrung-out bath sponge.

Why should I compost?

‘I don’t garden so why should I compost?’ This was what a friend said to me recently.

Where to start to answer this question?

Composting is an obvious activity for gardeners – you make your own top-quality plant food by recycling your organic waste.

 Like my friend, I too am no gardener.  I started growing a few things during the pandemic and finally realised when I saw the transforming effect of plants why gardeners do what they do.   

But the point I tried to make in answering my friend was that it wasn’t for the sake of plants that I started composting but for the sake of the soil itself.

A health soil sign that reads 'Healthy soil is the beating heart of organic growing - full of life and support life'.

 When I learned a few years ago what magical powers compost has in rebuilding the poor, degraded earth of the Earth, I realised that composting was a no-brainer.

The health of our soils is fundamental to life as we know it, but according to the charity Garden Organic, half the planet’s topsoil has been lost in the last 150 years.

And yet there’s something we can all do about it! Home composting might seem a small act on an individual level but multiplied by millions it’s huge.    

Climate crisis ally

For instance, did you know that one of compost’s superpowers is to help soil capture carbon in the atmosphere and pull it down into the ground? Along with oceans and forests, soil is an important carbon storage medium. And yet we’ve been letting the organic ingredients for compost rot in landfill for years, emitting greenhouse gases instead of capturing them. It makes no sense to throw nutrients away as rubbish when we can easily separate them to speed up the natural breakdown process.

 According to WRAP, the waste reduction charity, a home composting bin can divert approximately 150 kg per household per year of organic waste from landfill or treatment centres.

Save our soils

The minimum we can all do is to ensure that soil is not left bare. Bare soil is vulnerable to erosion, weeds and carbon loss.

  • Cover soil with mulch and just leave it. Chuck it on in layers of around 5cms. You can cover borders, around shrubs, trees and bushes. Worms will come up and take the compost back down into the earth where it will improve the soil structure.
  • Compost also helps worms to thrive, and they need all the help they can get, under onslaught as they are from chemical sprays, artificial grass and the paving-over of gardens.    
  • Give your lawn a boost by spreading compost thinly over it. Worms will pull it down into the soil, which will boost soil quality and by extension the grass.

Benefits for us

Michael Kennard (pictured) the founder of the food waste collection service Compost Club, has studied soil biology and is keen to spread the word about how soil is the foundation of our health. If we destroy it, it’s to our detriment.

‘Everything is a reflection of the soil,’ he says. ‘If the plants have that natural cycle going on, they’re really healthy. When we eat those plants, that’s what informs our gut health.’

Other benefits that compost provides include:  

  • preventing erosion
  • improving drainage
  • encouraging worm activity. Studies have shown that the simple act of introducing worms to degraded soil in poor regions of the world has increased plant yields by 280%.
  • preventing flooding. As more and more gardens are paved over there is less and less earth to absorb heavy rainfall. In order to slow down runoff and encourage water infiltration into soil, swap paving for plants and mulch, or ensure paving is permeable. In his book The Science of Gardening, Dr Stu Farrimond says that covering soil with mulches in late autumn protects it from pummelling winter rainfall (each bullet-like drop travels up to 20mph).

Benefits for plants;

Used on plants, compost holds on to important nutrients, improving the plant’s quality while also protecting it from pests and diseases.

 As compost breaks down further, it releases important nutrients into the soil, including the main nutrients that plants need: nitrogen, phosphorous, and potassium. Compost also increases the number and variety of beneficial bacteria and fungi in the soil, which helps plants to grow.

The ability of compost to absorb water is important as it’s able to slowly release water to grass and plants so they need watering less frequently. This is obviously vital in hot weather and droughts. Studies on compost’s water-retaining abilities have shown that for every 1% of organic matter content, soil can hold 16,500 gallons of plant-available water per acre of soil down to one foot deep.

Compost also helps water to get to plant roots more effectively by reducing crust forming on soil, so water can get into the soil more easily, and by helping to disperse water laterally from where it hits the ground, which means it will evaporate less quickly.

But I don’t have time to compost

Composting can be as time-consuming as you want to make it. If you’re pushed for time, go for cold composting.  If you want to invest a bit more time and effort, try hot composting, which means a wider variety of food waste can be added to the bin and compost produced faster.  

Or use bokashi bins, which ferment food waste thanks to the addition of beneficial bacteria in the form of a bran or spray. Once it has been left to ferment for a couple of weeks, this pre-compost mixture can then be added to a composter.

People whose local council operates a food waste collection might think, Well the council composts my food waste, so I don’t have to. But many people take the view that if they are already separating food waste to leave out for the council to collect, they might as well compost this valuable resource themselves at home for the benefit of their own garden or allotment.

 By 2026 all councils throughout the UK will have to comply with regulations requiring them to operate separate food waste collections.  

There are around 15 million gardens in the UK. We call them ‘our’ gardens but of course that portion of the earth isn’t really ours – we’re merely its custodians for a while.

Once you see the difference you can make to that tiny patch of the planet, without much effort, you can’t help but become a compost convert.

Julie

Spare Parts