Plums are wonderful at this time of the year. You can use any variety, but blood plums will give a beautiful ruby colour to the salad.
Note Farro is a whole-wheat grain. It's available from select grocers and health-food shops; if it's unavailable, substitute another grain, such as spelt or freekah. Baby amaranth is available from select greengrocers. If it's unavailable, substitute another baby herb.