In bowl, stir together yogurt, dill, mint, chives, juice, garlic, and salt. Let stand 15 minutes or refrigerate up to 12 hours.
Before serving, stir in cucumber. Season with salt and black pepper. Top with dill sprig. Serve with assorted vegetables. Cover and refrigerate leftovers; stir well before serving.
Suspend small colander over bowl. Lime colander with three layers cotton cheesecloth or a paper coffee filter. Spoon in yogurt. (Use yogurt without gums, gelatin, or fillers to ensure whey and curd separate.) Cover with plastic wrap; refrigerate at least 24 hours. Discard liquid. Makes about 3 cups (24, 2 tablespoon servings).