Raw baby artichokes, which have a nutty crispness similar to that of celery root, complement the mild, tender white asparagus in this hearty salad.
Cover farro with 3 inches of water in a large saucepan; bring to a boil. Reduce heat to medium; cook until farro is tender but still slightly chewy, about 25 minutes.
Combine lemon zest and juice, oil, onion, 2 teaspoons salt, and 1/4 teaspoon pepper in a large bowl. Drain farro and immediately toss with dressing. Let cool completely.
Meanwhile, squeeze remaining 2 lemon halves into a large bowl of water; add rinds. Working with 1 artichoke at a time, remove all tough outer leaves. With a serrated knife, cut off top 1/2 inch; with a paring knife, trim and peel stem. Very thinly slice lengthwise. (Transfer to lemon water as you work to prevent discoloration.)
Drain artichokes; pat dry with paper towels. Toss with farro, asparagus, mint, and dill. Serve with feta, drizzled with oil and garnished with more mint and dill.