[AmityvilleHams]

Cat grass and soil are both unacceptable substrate choices. They can harbor parasites, put you at risk of fungus etc as souffle mentioned, and they hold far too much moisture. Hamsters need lower humidity in the cage. Even organic soil also has unsafe ingredients - fertilizers, even organic ones, are just one tiny example of things that are completely unsuitable for hamster use. Just in case, live plants in general should never be placed inside a hamster enclosure either. These also end up adding moisture to the environment and provide all sorts of potential issues of their own.

You'd unfortunately need a deep clean to get rid of all the unsafe substrates but a pure paper substrate(no baking soda, odor control additives, etc) would be a good choice for the entire cage. Hemp is another great option, but be careful of the brand as some hemp substrates will have unsafe additives such as citronella. Aubiose would be an excellent choice though as it is pure hemp!

I know there have been people saying soil is fine especially with popular hamster youtubers even recommending it, but it is just not safe and really needs to be removed completely from any hamster enclosures that have it. A high quality pure coconut fiber can be a suitable alternative - if and only if given in very small amounts in a container in a cage with excellent ventilation as well as not being kept too dry or too moist.