Mellow Compost Lab

Preparation & Maintenance

Essential initial and routine activities during the Active and Cooling phases to enhance the quality and speed up the finished compost to maturity.

Here, we discuss two different steps (setup and regular maintenance)  in the compost cycle.

  1. The first one is the preparation of waste (top-ups)  in the Active phase prior to adding it to the compost bin.

  2. The second is a recurring maintenance  step that involves (1) measurement (recording) and (2) stirring/mixing when & where appropriate.


A proper preparation of the waste mix is critical  to the success of the composting cycle and the resulting quality of compost. This is done every week or fortnight depending on the season; so in the warm season; when there is more garden waste in addition to the kitchen waste, we undertake waste preparation about once a week; in cooler seasons this could be on a fortnightly basis or longer. Holiday trips or prolonged weather conditions can also alter these periods.

Waste mix tends to take place towards the end of all the garden activities (in particular in warmer season); when all the garden waste is assembled. For the kitchen waste, I also do a quick check to see if other non-organic material made their way to the kitchen bin by mistake. Then I remove these. At home we have two bins side by side; one for compost waste and the other for everything else. But mistakes happen.

  • To prepare the mix, we use a wheelbarrow as the main container where all the ingredients go in. For large volumes of waste, we work in batches using the wheelbarrow a few times (or sometimes we use the second wheelbarrow).

  • First we need to prepare the green and brown material to the right size: Where possible, we shred these to “bite” size, roughly 4x4 cmmax, the smaller the better.  For this we use mainly garden shears, pruning clippers and secateurs. In some instances, we also use a  power shredder for larger volumes (typically for hedge trims). We have also used a lawn mower when the material is dry and does not contain thick stems (or these are first removed and cut with hand tools).  

  • We throw  in green and brown material in some proportion based on the target Carbon: Nitrogen (C:N) ratio (~30). Then we add  water and any of the optional extras. We mix with a garden fork, ensuring all ingredients are  well mixed. Contact between green and brown material encourages the bacterial and chemical reactions for a quicker and better compost. Some fine material such as grass or coffee ground need to be well mixed to avoid lumps. The calculations for the C:N ratios were done in the early years to get proportions right and after that experience and approximation took place. From time to time, we get back to the C:N table as a refresh of the values. The visual and smell checks also enable to tell us whether we are within the desired C:N ratio range.

  • We also often add other elements (optional extras), typically a handful/cup of soil, coffee ground, chopped sticks and twigs and compost sieved residues (SR). This is optional and depends on availability and needs. The soil and coffee grounds encourage bacteria and worms to come in (worms love coffee grounds). Sticks, twigs and SR  help create air pockets in the pile. In particular when grass is added in significant proportion in the mix, these play a key role: Grass is dense. Air (oxygen) is vital to the success of the decomposition process. Also remember as we pile these, there is a natural compaction, it reduces the air pockets (hence the need to aerate and mix on a regular basis).

  • We use our standard size buckets to pour  the waste material  from the wheelbarrow to the designated compost bin. For a measurement perspective, we shake all the material in the buckets so that it settles well and then level it up to ensure consistency in the measurements (pression and volume, the filled up buckets are levelled with a ruler).

  • This activity may take an hour to a couple of hours depending on the volume of material available. This could be as simple as just a couple of kitchen waste buckets (in cold season) to a few 40L containers of grass, garden trims & rejects and shredded shrubs and hedges.

Maintenance Activities

Measurements:  One the first activity in the compost related activities is measurements across all the bins (depth of the bin material for volume calculations and temperature). We first hand rake the top level of the bin to level it  as much possible then take 3 to 4 readings at different places and average them. We use the depth measurement to calculate the volume of compost in a bin using the geometry and dimensions of the bin.



Stirring & aerating the bin: An important routine task to perform regularly during the first three phases of the cycle:  The bin is stirred regularly to aerate the pile (oxygen) and help green and brown parts to be in contact for further composting. It is not required to add water to the pile (as  we don’t live in a hot region). But if the temperature has been hot inside the bin for a while, a visual examination of the pile (dry'ish) would require some watering. Also, a quick check on visuals and smells is key for green/brown balance.

  • For stir mix, we use three different tools: (1) Compost mix & aerator; (2) garden fork and (3) a long (4ft) metal rod. The most important tool is the aerator (image below); it is a purpose built long metal stick with a corkscrew-like end and is very important in aerating a bin.

  • We normally select between 4 and 8 (geometrically spaced) spots on the surface of a compost bin and insert the aerator and pull back. This pulls the bottom part of the compost and creates air pockets when pulling back. For small bins, we select 4 areas; normally centre + 3 areas; and for the custom built larger bin (E), we poke the screw the aerator in 8 different areas (in 2 rows of 4 layout).

  • The garden fork helps to bring material from the edges and side of the bin towards the middle. The thick metal rod is inserted  and then rotated insitu to leave air holes all the way to the bottom. Sometimes, additional coffee ground (and water) is added to the vertical holes (Active period only).

Further measurements: Once all the activities of mixing, stirring and aerating the bin is complete, and any top-up  added to the pile, we take a further depth measurement: this will serve to assess the level of compaction (when  topping up a volume of waste) and also the decay rate  against next reading.

Temperature: There are at least two conditions when a bin is not stirred or mixed.  The first one is the hot condition: That is the bin is still heating up and has not completed its thermodynamic stage. We do not want to disturb the intense microbial activities. We measure temperature and volume as a matter of course; and any bin whose temperature is greater than 30℃ is left alone for a week. However, any operating bin is mixed if it has not been stirred/mixed for about three weeks. The second condition is frost. We can see prolonged periods of sub-zero temperatures in Leeds. During these periods we simply do not touch the compost bins.


We measure the temperature at different points inside the bin (called PoI for Point of Interests). Because we top-ups waste volumes at different periods of times and then mix; the compost bin will have compost areas under different stages; the bottom part would have past the thermophilic stage and start to drop in temperature; whereas the most recently waste added top-up  (say within the last week or so) will still be in thermophilic stage. The temperature is taken at the centre of the more recent volume added. At the next round, the recently added material will be mixed with the rest of the pile before the new top-up and the cycle continues.

Below is an example of a compost bin at three consecutive periods where top-ups were added. Note from one period to another, the top level drops off (due to decomposition).


PH: Towards the end of the cooling phase, when the bin is nearly ready, home-made wood-ash or lime could be added to the pile. It helps neutralise the PH and adds potassium to the compost.  A good part of our kitchen waste is citrus and related fruits. We look at the IW distribution for that particular bin and if a higher than average proportion is kitchen waste, the two additives help balance the PH.