The Role of the Bulking Agent (woodchip/mulch)

The Role of the Bulking Agent (woodchip/mulch)

All you need to know about adding a bulking agent on your HOTBIN

The role of a wood-chip bulking agent (mulch) is to create structure, air spaces and gaps to improve airflow throughout the waste inside the HOTBIN composter. It will also compost down in time, but you may find larger chips visible in your final compost. Wood can absorb moisture and does not change shape thus maintaining good airflow inside the unit.

The HOTBIN requires bulking agent or equivalent garden wood chips, to keep the bin well aerated and the bacteria fed with oxygen. The structure of the bulking agent is such that it creates air pockets in the waste allowing oxygen to flow around the heap to keep the bacteria composting aerobically and efficiently and also helping to keep their anaerobic cousins at bay!

You can purchase your own wood chips from a nearby store, or make your own by cutting up pruned woody waste or twiggy plant material from your garden when needed.

How much is enough

As a rough guideline we recommend that you add an additional fifth of bulking agent to whatever quantity of waste you are adding. So if you add 5 handfuls of veg peelings into the HOTBIN, be sure to add 1 handful of bulking agent.

IF you are adding lots of wet material such as grass which can become matted, you may want to add a little more.

IF you are adding lots of dry woody material you may wish to add less or none as this material already has bulk to it.

NOTE: Every HOTBIN is different due to the types of waste being added, but the ratios advised are a good starting point.

Adding bulking agent

After adding one fifth Bulking Agent use the rake provided to lightly stir it into the top layer of fresh waste. Doing this helps to evenly incorporate the chippings throughout the heap resulting in a more consistent airflow.

What is the best particle size for bulking agents?

Small to medium irregular particles increases the surface area and will compost down to form part of the final compost. Large pieces may be visible when it comes to harvest you bin, if that is the case you can always throw them in at the top and cycle them through for another 90 days. Larger particles create big gaps and very small particles (fines) tend to compress filling gaps, fines will be lost and just blend in with your compost. Note if your bulking agent is to fine and dusty this can have the opposite affect and inhibit airflow.

What is the correct water content of bulking agents?

Bulking agent should ideally be dry. Just remember that the role of the bulking agent is to maintain good airflow inside the HOTBIN.


More on bulking agent, starting and feeding your HOTBIN on HOTBIN User Guide

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