This is another humidity issue. The type of mold that grows on Cat Grass, usually seen at the bottom of the blades close to the roots, is completely harmless. One often sees this type of mold on organic produce – and you can just rinse it off under the tap, then allow the plant to get some fresh air and all will be well.
Occasionally, if not noticed right away, the mold can turn from white or gray to black. This black mold is harder to rinse off, and it can start to smell bad. When this happens it’s best to just dispose of the affected pots.