Prepare the artichokes:
Bring 1 quart water, the vinegar, garlic, and salt to a boil in a 4-quart saucepan over high heat. Add the artichokes and boil until tender (check near the base of the leaves), about 10 minutes. Drain the artichokes (reserve the garlic), and lay them out on a cloth to dry for about 30 minutes. Put them in a 1-quart container or Pyrex measuring cup. Add the garlic, parsley, thyme, and oregano and cover with the olive oil. Let sit for about 1 hour.
Make the salad:
Reserve 1/4 cup of the oil and drain the rest. Discard the garlic and herbs.
Bring a 4-quart saucepan of well-salted water to a boil. Add the farro and cook until al dente, 25 to 30 minutes. Drain and spread on a baking sheet to cool until barely warm.
Combine the farro with the artichokes, the reserved oil, feta, and scallions and toss to combine. Let sit for 10 minutes to let the flavors meld. Toss in the watercress and vinegar. Season to taste with salt and pepper and serve immediately.
Photo: Scott Phillips