Interesting question from Janet:
I have an open bin of worm castings under my flow through bin. I discovered my cat has been using it as a litter box. I am wondering is the urine harmful to the castings or can it still be used in the garden? Also, is it bad to let stored castings dry out? Does this affect the microbial life?
I hope you don’t mind that your email made me laugh a bit! I definitely feel your pain – our old cat Monty (who passed on last August) was peeing everywhere during his final months. I didn’t have any low-lying castings bins at the time, but I guarantee he would have “fertilized” them if I did! lol
Getting back to your question…
I would say that it probably depends on the amount of urine, and whether or not there are…uhhh…other deposits in there as well.
If the material soaked up the urine and it’s not wet, I think it would be totally fine. The microbes in the castings would likely help to convert the urea in the urine to plant-usable forms of nitrogen.
If you end up with muddy castings and/or there is feces in there – it might be better to dump under some bushes rather than using for prized ornamentals or food plants. My guess is the urine could have a fairly high salt content, so having too much would likely harm more sensitive plants. And the feces can of course have pathogens in it.
As for drying – I’d avoid letting the castings dry out completely. i.e. they should never get crispy or dusty. This will likely harm the microbial life.
Aim for somewhere between this level of dryness and “muddy”.
In other words – not really moist to the touch, and fairly crumbly.
Hope that makes sense!