3. May, 2020

Aerating Compost


 Aeration is necessary to provide the composting microbes and larger creatures  with the oxygen necessary to convert the  organic matter into compost  and to achieve the  temperatures necessary for the more  rapid decomposition of hot aerobic composting.

If the material is not aerated  composting will still happen but will take longer, a year or 18 months in some cases, and may become anaerobic.  Aeration by turning the composting material will involve extra work but I believe it is worth it.

If using pallet or New Zealand bins without a front, or where the front panels can be easily removed, the material can  be turned from one bin to the next using a garden fork. However, there are other techniques and bins  which avoid the need to turn the contents and as some of these are applicable to the entry level Dalek bin. 

1.  Building air into the  bin

  • Aeration at the base

Mount the bin or pile on  an old pallet, this will need replacing as it rots but is easily checked when the bin is emptied, or build a base out of good quality wood about 3-6 inches off the ground to allow access of air into the base. The slats need to be spaced to allow entry of air but sufficiently close together to prevent the entry of rats and other vermin. 

  • Aeration via the base layer

Start the composting by creating a base layer of twigs or small branches from pruning shrubs, brassica stalks etc  as a base level to allow air to flow up into the compost. This base layer  will not rot down as quickly as the rest of the material and may make it difficult to empty the bin using the hatch but if this is a problem a Dalek type composter can be knocked over or lifted of the compost when harvesting.

  • Aeration with sticks

Some add more twigs and scatter them throughout the pile to assist in aeration but this approach is only  applicable if the contents are not to be turned  as the sticks make it difficult to makes it more difficult to turn the pile using a fork.  Another source suggests that if building a heap or pile, rather than filling a bin,  long sticks could be laid horizontally to crisscross the heap at different levels with hand holds protruding from the pile.  As the heap matures the ends of the  of the sticks can be turned, lifted and shaken to help aerate the pile .

  • Aeration  by browns and bulking agent

At home with a small garden and a steady supply of food waste (nitrogen rich greens) you may opt for a system whereby a kitchen caddy of material is added to the bin every few days with cardboard or shredded computer paper as the main source of browns. If this is the case air spaces  can be built into the heap by adding egg boxes, the cardboard tubes from  toilet and kitchen newspaper   and crumpled corrugated cardboard. The addition of a bulking agent.  such as woodchip. absorbs water from the food waste and helps maintain the air spaces.

 Hotbin advise that in their bin the correct use of a buking agent, such as partially composted woodchip, will provide and maintain  sufficient air spaces for the bin to work effectively. This passive aeration occurs  where rising hot air pulls cold air into the  heap.

2.    Aeration systems

Some of the more expensive bins, such as the Aerobin 400,  have a central aeration system which is said to do away with the need to turn the compost. Home composters can create their own aeration tube by   drilling holes in plastic downpipe and placing this in the centre of the bin as soon sufficient  material has been added to keep it vertical added. 

3.    No-turn pallet bin

It is possible  to make  compost in a traditional bin using a good combination of green and brown layers without turning and still reach a temperature approaching 80°C.  Shewell-Cooper described one such a system in 1972 and more details are given at http://www.carryoncomposting.com/443725799

4.    Turning the contents

  • Hot Composting

In order  to create finished compost in a short time and to kill seeds  and perennial weeds hot composting is required with  the contents of the bin being turned regularly during the initial  stages.   This can be at fixed times or every time the bin temperature drops below 40°C (or about 100° F)

Hand turning using a garden fork (bin) or pitchfork (heap)  can be used to  home compost in a heap,  New Zealand box or pallet bin particularly if the material is being transferred to an empty adjacent bin. It is easiest to move the material from one bin to another.

  • Windrows
  •  In a large garden  windrows may be used to compost. Shredded mixed garden waste, such as grass cuttings, pruning and leaves.  The windrows are turned on a regular basis to aerate the  content with the outer layers binge moved to form the core of the new windrow  with the material from the centre of the established windrow being placed round it.
  • Cool Composting

If using the slower  cool compost approach adding a mixture of brown and green materials to the bin weekly as they become available requires less effort but may not kill weeds. Under this type of composting the organic material at the bottom of the bin is ready for use after about a year while the top layers always consist of relative fresh waste. The material is often not turned, and harvesting is through a  hatch at the bottom of the bin. Some  composters, usually those with several bins, do turn the  do aerate  the material by lifting the bin off the compost and refilling it.  

Alternatively, a compost aerator tool can be used. This usually  consist of a metal rod handle with some hinged metal arms with  teeth on the end. This is plunged into the compost and   the teeth will open out as it is pulled out and create air  pockets inside the compost. A second type have a large corkscrew on the end which is turned into the compost. There are photos on the above webpage  

  • Compost Tumblers

 If using a compost tumbler, the material is turned and aerated by turning the whole drum  it also helps to control the moisture content of the material  to prevent the compaction that may occur in wet material. The effectiveness of this type of compost bin at aerating the material varies with the shape of the bin, the shape of any internal bars to break up lumps, the moisture content and  the weight of the bin when filled to working capacity. 

Further information can be found at http://www.carryoncomposting.com/443725799