Composting at Unimelb Community Garden

A long time ago, an Australian friend I met in Peru told me about home composting. By my previous experience with windrow composting, I could not imagine how an odorous and high-volume process could be performed at a home’s garden. In Australia, garden waste is sent to composting facilities, but food waste is encouraged by authorities to be composted at home.

The University of Melbourne Community Garden composts the food waste donated by some students and offices in composting bins. The composting bins are bottomless barrels in which food waste and coffee chaff (sometimes dried leafs) are added daily in similar proportion until the composting bin is full. Then, the composting mix is left resting for about one month.

Food Waste

Compost

Not much technical data has been retrieved from this process, but here are some facts about it:

1 – The process works. However, it does not reach enough temperature to destroy wild herbs seeds and thus, not all vegetable pathogen is killed. However, this situation can be improved by turning the compost, so the upper part goes to the centre of the barrel. The Community Garden uses a tool that facilitates this operation.

2 – Coffee chaff is mixed with food waste in similar proportions (weight) because a proper composting has a carbon: nitrogen relationship between 20:1 – 30:1. Food waste contains a very low C: N relationship which is why it needs to be mixed with a carbon-rich substrate as coffee chalk to get to the proper C: N relationship. 

3 – The process releases unpleasant odours. People who have worked doing composting before, like me, might not sense the odours, but the ones who are not accustomed to the scents of this process may be very sensitive. Odours are released when opening the lid for feeding and especially when turning the compost. The carbon source reduces the odours, so make sure you count with the carbon-rich substrate when composting at home.

4 – You do not obtain mature compost after one month. After one month, the compost is still young and may be added to the soil, so it degrades in it. The problem here is that because of the low aeration, high moisture and low carbon, compost may not be ready yet and the process might have to continue for more weeks. Mature compost requires more than one month, but after one month you may be wanting to use the composting bin for a new batch.