I have multiple groups of cat grass for decoration. They're about 6 months old and some of the leaves died, making it less appealing. Since there are a lot of them, what would be the best way to get rid of them quickly? I don't want to cut them one by one.
Assuming you mean what is usually meant by "cat grass" (grass intended for indoor cats to nibble on:) Start new "cat grass" (typically oats) - pull up the old, dying stuff, put the new stuff in its place (compost the old.)
It is a grain with a "less than 1 year" lifecycle. Trying to keep it alive for a long time, it will inevitably look bad.