Get to know your carbon wastes for composting success

Carbon is an essential macronutrient in composting. It is found in various forms in organic wastes. Since some forms compost faster than others, knowing which is which will help you compost better.

Organic wastes are sorted as either rich in carbon or nitrogen by convention. Your compost system determines how much of each type can be used together.

Sources of compost carbon

For compost bins and tumblers, carbon-rich wastes make up two-thirds of the waste composite. Not all are there as a nutrient source for compost microbes to feed on. Some of them serve as bulking agents, creating air pockets to supply oxygen. Others absorb water, helping to keep the wastes moist.

Bulking agents are typically woody materials. They contain high levels of carbon but in a form that gives strength and rigidity, to provide structure for air gaps. This carbon takes a long time to break down, and plays a relatively inert role. In fact, these woody parts can be sieved out and reused in the next batch.

Bulking agents are poor water absorbents. So, high-absorbency wastes, e.g. torn cardboard and egg cartons, are handy for retaining moisture while their carbon is slowly used in the composting process.

Garden waste is the usually the main source of nutrient carbon in standard garden compost systems. This carbon is used to keep microbes alive and create new life.

Don’t forget fresh air

Compost microbes need oxygen to live. Air pockets created by bulking agents contain oxygen, but regular aeration by mixing is required to bring in fresh air. Without manual mixing, composting in compost bins and tumblers slows as oxygen runs low and ceases when depleted. Even worse, odours are emitted.

An easy solution

A well-ventilated compost system eliminates the need for manual aeration, and by extension, the need for bulking agents to provide air pockets. Woody materials like wood chips have an alternative use as long-lasting mulch in gardens.

High-absorbency waste is also unnecessary in a well-ventilated system, which is designed to generate a hot and humid environment that suits compost microbes. This is created when composting wastes with high water content like vegetable and fruit scraps.

The carbon in kitchen scraps is generally available for composting, so little is left unused if carried out in the controlled environment of a well-ventilated system like Bioverter. Compared with garden waste, kitchen scraps can be transformed quicker into richer plant nutrition.