Ferroseed in Pokémon GO is the chosen Pokémon for March's breakthrough research reward. The Thorn Seed Pokémon will be available for the entirety of March before Niantic chooses a new Pokémon for April. As with any Research Breakthrough, you must complete a Research Task seven days in a row. Then you'll be rewarded with Ferroseed, a possible Sinnoh Stone, and 5,000 Stardust.
However, is Ferroseed worth farming? Depends on who you ask.
Ferroseed Pokémon GO: Niantic Labs Reveals March's Breakthrough Pokémon
Ferroseed evolves into Ferrothorn with 50 Candies but the Pokémon is not a main Pokémon in the meta. Players will not use either one in the Ultra League and probably won't even use them for Gym battles. It's basically a Pokedex filler for many.
At least the last research breakthrough Pokémon was a brand new Pokémon everyone wanted. Ferroseed has been out for sometime and it still hasn't found a place on most teams. While the game has plenty of new content every month and a pretty popular Pokémon planned for March's Community Day, the Research Breakthrough Pokémon was a bust.