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Practical guide
Vermicomposting
Guide contents
01Getting started5▸
02Choosing your model5▸
03Daily care4▸
04Solving a problem4▸
05Living with your wormery6▸
Other topics in the guide
Bad smells in your wormery: causes and solutions
A wormery that is working well smells of almost nothing — at most a faint woodland smell, which is precisely what makes it such a good companion indoors. If you notice a strong or unpleasant odour, however, it is a signal to take seriously: not a lost cause, but an imbalance to correct quickly.
Where does the smell come from?
Your worms and the micro-organisms that live alongside them need oxygen to break down waste cleanly: this is aerobic decomposition, which is virtually odourless. When air no longer circulates enough — compacted bedding, too much moisture, too much waste added in one go —, some areas of the wormery switch to anaerobic decomposition: other micro-organisms take over in the absence of oxygen, and they are the ones producing the foul-smelling gases you notice. In the vast majority of cases, the cause is simple: you have fed your worms faster than they can digest, and the surplus has fermented before they had time to deal with it.
How to fix it
If a strong smell is coming from your wormery, here is what to do: remove the surplus undigested waste from the active tray, then add a good amount of paper or cardboard — this dries out the environment, brings carbon back in and helps air circulate better. Then stop feeding your worms for at least a week: long enough for them to catch up and digest what is left. All that remains is to be patient; the smell usually disappears within a few days to a week.
Willy's tipGently stirring once a week is generally enough to prevent this kind of imbalance, by stopping the waste from compacting and forming air-starved pockets — we explain how in our guide Should you stir your wormery?
Prevention is better than cure: the right routine
The best way to avoid this problem is never to feed your worms faster than they can digest: it is better to add a little waste every day or every week than a full bucket all at once. Also make sure you always keep the balance between nitrogen-rich waste and carbon-rich materials (paper, cardboard) — we explain this routine in our guide What do earthworms eat?
More than a nuisance: a real risk for your worms
A bad smell is not just unpleasant for you: an environment that stays starved of oxygen puts your worms in real danger. Anaerobic micro-organisms do not just produce unpleasant odours, they also release toxic substances, such as ammonia, which can quickly kill your worms if the situation persists. That is one more good reason to act at the first signs, rather than waiting for the smell to go away on its own.
In summary
A faint woodland smell is perfectly normal; a strong odour almost always signals too much waste or poor aeration. Remove the surplus, add cardboard, leave it for a few days: in the vast majority of cases, everything quickly returns to normal — and your worms will thank you for acting fast.
