Mellow Compost Lab

   Bin Cycle Phases   

A bin cycle is a four phase life-cycle to decompose organic waste into finished compost 

For our home composting, each bin cycle is made up of four phases: Active, Cooling, Maturing and Empty. A cycle sees  a compost bin filled up with input waste and goes through all the conversion and decomposition stages to completion.  Every time we start a new compost bin we call it a new cycle and assign it a new (unique) number (incremental). The Mellow compost lab has so far completed 56 bin cycles.


This is the start (first phase) of the cycle, a top-up period where we add waste material to the bin. This often happens on a weekly basis (or about) weather and other events permitting. The waste material added to the pile needs to be prepared, that is green and brown material shredded to small size and mixed. The green/waste material is combined with an aim of a C:N ratio as close to 30:1 as possible, Fill-up waste content is measured in bucket size and added. Stirring and mixing is an essential part of this phase, to aerate the pile, encourage green and brown material to mix; Stirring is not performed during frost season or if the waste pile is hot.

Using long term averages (12 years and 56 bin cycles completed at the time of writing); the active period lasts ~3.5 months  and  ~2.1 x bin size  worth of waste is added over this period (as the waste pile reduces over time).  The Active period could be much longer (in winter) if there is not enough waste material to meet the minimum ~2x bin size. It can also be shorter if there is a peak supply of waste (summer) and the 2x bin size is met rapidly.  As a heuristic rule, we keep the active phase for at least  3 months and sometimes the input waste ratio exceeds 2x bin size. If after both conditions of period and volume have been met, the bin is still not full, we might continue filling up to maximum if we know we won’t need the compost in the next couple of months. 

In Compost Science & Engineering, the Active phase initial period comprises two sub-phases: mesophilic and thermophilic. The first one is the initial activation phase (temperature normally ramps up) and thermophilic phase where temperature can reach 65℃. Both sub-phases last about a fortnight maximum depending on volume added, green/brown ratio & type, size of material (shredded)  and container type.


In this phase, no more organic waste is added (no more fill-ups). The temperature would have dropped across the bin (to the ambient/outdoor temperature), worms are the main residents actively working. When stirring the bin, one can easily see the number of worms working. One test that the cooling period is coming to an end is when the number of worms diminishes; which means their work is finished (and they went elsewhere to find new food). Stirring and mixing is still an essential part of this phase, ensuring that any last part of green or brown not yet decomposed are in contact. Normally visual tests are used to see crumbled and nice/soft brown compost (and no smell except earthy ones). At the end of this period, the compost could be emptied and is deemed “ready to use”

Periods: Long Term averages


The maturing phase is optional ( additional), to allow further decomposition for a more refined compost. It is not necessary for the compost but useful as an enhancer to the quality of compost: It is normally used if/when

  1.  the compost material is not immediately needed,

  2. there is no place or time to empty or store the finished compost (at that point in time) or

  3. the bin space is not needed for awaiting or soon-to-arrive waste material.


Period where the compost bin is waiting its turn to be used again.  In general, we prefer to keep the compost in the maturing phase as long as possible unless for example

  1. it is needed shortly (to be used),

  2. the compost bin is needed for further use or

  3. weather and other conditions suggest it is better to empty because storage is available.

As part of the MCL project, we added this phase in the cycle to study capacity planning and occupancy rates.