Strong ammonia smell drifting across the garden

[Dr Mike Oxgreen]

My HotBin is running very nicely at 60 to 70°C.

The only problem is the smell it's making: a rather pungent ammonia smell that drifts across part of our garden, and I'm worried that our next door neighbours will complain when they work out where the smell is coming from!

I've had the HotBin about 18 months. I don't remember having this problem in the early days. Does the odour filter bag in the lid need replacing after a certain time? If so, what does it contain - could I use a bagful of aquarium zeolite, which absorbs ammonia?

The other option would be to cool it down a bit; is there a way of controlling the temperature so that it doesn't run quite as hot, and would that reduce the amount of ammonia being released?

I do compost quite a lot of nitrogen-rich grass clippings, which is a major part of the reason why it runs so hot, and probably the reason for the ammonia. I'd like to continue recycling those nutrients, but I really am worried the neighbours will complain sooner or later. Grateful for any advice!

[EnlightenedElm]

Hi there,

We're pleased to hear that your HOTBIN is running at the top end of the hot composting temperature zone.

Unfortunately, a strong ammonia smell is quite a common occurrence when people compost a large quantity of grass in any compost bin in one go. Are you adding any other types of waste in with your grass cuttings at all?

You also question whether the bio-filter may need replacing and the fortunate answer is that the HOTBIN's bio-filter should not need replacing at all. On this occasion, the likely reason for the detection of the strong ammonia odour is that your HOTBIN's filter has temporarily been overloaded by the large volume of grass which has recently been added to the unit. The ammonia can be more detectable on some occasions, depending on the amount of grass added, whether any other types of waste are added with the grass and whether there is any breeze outside the unit to help disperse the odour.

For those users who do experience an ammonia bio-filter overload, please be assured that the filter should be able to recover and begin filtered out the ammonia within a couple of days.

You can reduce the HOTBIN's internal temperature by reducing the amount of grass cuttings you add into the HOTBIN on a single occasion. Could you store some of the grass cuttings after mowing the lawn and add them in a couple of days after the first lot?

[Dr Mike Oxgreen]

Yep - I do spread the clippings out after mowing - it allows them to dry out, which helps prevent excessive moisture. The top layer of clippings becomes quite desiccated in the sun and wind. I then add the clippings in stages over the course of a few days. I also add food waste, plus other gardening waste like shrub prunings etc. And compostable cat litter, some of which has been weed on - I guess that will increase the ammonia issue, but the litter also helps absorb moisture. The cat litter only partly composts, but gives the material a nice crumbly texture.

I have tried tearing up corrugated cardboard in the past, but boy is it hard work!

The problem is purely because I'm composting such nitrogen-rich material.

I noticed on the HotBin web site a suggestion to place a bag of zeolite-based cat litter on top of the vent on the lid. I might try that.

[EnlightenedElm]

Yes, the odour is unfortunately because of the volume of nitrogen rich material you are adding. Can I ask whether you add shredded paper or torn cardboard into the HOTBIN each time you add fresh waste as well as some woody material?

We are not sure where on the HOTBIN website you found a suggestion for the zeolite-based cat litter - we would strongly advise against trying this. The reason for this is that if you place anything over the valve you could cause restricted airflow within the unit and create further problems. It is best to try and treat the cause of the odour rather than the effects!