Three things are essential to the composting process: moisture, temperature, and oxygen. The microorganisms present in composting systems thrive on oxygen, and worms breathe through their skins, so there must be sufficient oxygen in their habitat to sustain them. If you’ve ever seen worms out on the sidewalk during a downpour, this is why - their normal underground habitat has become saturated with water and they can no longer breathe there.
If you detect a foul odour when feeding your worms, your wormery could be too wet and not getting enough oxygen.
Aerobic vs. Anaerobic Bacteria
Aerobic bacteria require a lot of oxygen and moisture to survive, and they do not give off a bad odour. This is the kind of bacteria that should be prevalent in your vermicomposter – they help worms break down food and thrive in the same conditions that worms enjoy. If your vermicomposter gets too wet and does not have enough oxygen in it, anaerobic bacteria will take over. These are the bacteria that give off a terrible odour. If you notice that your bin smells bad or is too wet, it means the anaerobic bacteria have moved in and set up a home. For information on how to correct a smelly or waterlogged bin, see Wormery Moisture
Adding Oxygen to Your Wormery
In order to increase the oxygen in your wormery, add materials that promote aeration and drainage. These can include pumice, coconut coir, and small chunks of cardboard or paper egg cartons.
You can also “stir” your composted material, food, and bedding with a gardening hand fork or your fingers to loosen up clumps and increase airflow.
You can stir your compost with a hand fork to increase aeration.
A third option to increase airflow in your wormery is to separate the trays for a short period of time. You can do this by lifting them up and placing thin sticks or paint stirrers between them. Don’t do this for more than a few hours, though, because you don’t want your system getting too dry.