David Kenny asks if he can make garden compost from the contents of his cat litter tray. The general consensus (including advice from local councils) is that the best thing to do with the contents of a cat litter tray is to bag it up securely and dump it in the landfill bin. Most cat litter is clay-based, so even if the solids were removed and flushed away, the contaminated clay would not be a suitable compost bin addition. Animal manure from carnivores such as cats and dogs is bad for garden soil, full stop.
Only grass and vegetable eating animals, such as poultry, rabbits, guinea pigs and farm animals provide us with anything that is good for the garden. It can be bagged up or stacked up and covered with plastic, and will take six months or more to rot right down (at which it point it will be pongfree and safe around plants.)
Alternatively, smaller quantities of manure from herbivores (including paper or straw bedding from pets’ cages) can be added straight to compost bins, where it will rot down with everything else and add valuable nitrogen to the final mixture.