Solomon has employed at least a few people to find a mutated fern for him. The plant is fantastic for synthesizing radiationmedicine. While he doesn't explicitly mention sending anyone else, he has sent at least one other person to the Forest Grove Marsh, but they did not return with ferns in hand.
The quest is a simple fetch assignment. Mutated ferns are reliably found at the Forest Grove Marsh. Harvesting and bringing one back to Solomon is worth 100 caps (the player can haggle up to 200 caps).
↑The Sole Survivor: "Looking for a job, if you got one." Solomon: "Yeah, I got something. Looking for a Mutated Fern if you find any.I hear some grows out near Forest Grove Marsh. Natural radiation sucker. Be great for cooking RadX or RadAway." The Sole Survivor: "What did you need again?" Solomon: "Mutated Fern. Hear it's dynamite for making radiation meds. You interested?" (Solomon's dialogue)