Lv 45
Ferroseed does evolve in Ferrothorn at level 40.
Ferroseed evolves at level 45
You train it to level 40
Level 40 ;-)
In Pokémon White, Ferroseed will evolve at Level 40.
Ferroseed evolves at level 40
It evolves by leveling up. Ferroseed evolves into Ferrothorn at level 40.
Ferroseed will evolve into Ferrothorn.
Train it to level 40.
In Chargestone Cave you find Ferroseed and evolve it at level 40 to a Ferrothorn.
Ferroseed evolves into Ferrothorn at level 40.
Through leveling up; Ferroseed will evolve into Ferrothorn at level 40.