In a small bowl, whisk together buttermilk, mayonnaise, sour cream, dill, parsley, garlic, onion powder, salt, and pepper until smooth. Cover and refrigerate for at least 30 minutes to blend flavors.
In a large salad bowl, combine mixed greens, cherry tomatoes, cucumber, carrots, and red onion.
Drizzle desired amount of ranch dressing over salad and toss gently to coat. Serve immediately with extra dressing on the side.
Tips
For a lighter dressing, substitute Greek yogurt for sour cream.
Store leftover dressing in an airtight container in the refrigerator for up to 1 week.
Add other vegetables like bell peppers, radishes, or avocado as desired.