The first way to tell if your arugula is terrible is by its color. When it loses its green color, it loses a significant portion of its nutritional value. Then, if it looks wilted or brown, it’s too old. It might also smell bitter or sour, and it may even be too tough to cut or eat.
The best way to tell if arugula has gone wrong is to look for signs that it’s gone bad. It will become slimy, mushy, or turn brown. If it has lost its color and smell, it’s time to discard it.