Possible Clues:

• Mesclun, and a hint to the circled squares
• Simple salad ... and what the starts of the five other longest answers are?
• Salad choice, and a description of the first words of the starred clues' answers
• Words in a salad description
• Packaged produce buy, and a literal description of the ends of 17-, 28-, 39- and 49-Across
• Salad choice, and a literal description of the starts of the answers to starred clues