To evolve your grotle into torterra, just level it up to Lv. 32.
Get that?
LEVEL32
lv:32
He evolves at level 32 in Pokemon platinum
Grotle evolves into a Torterra at level 32.
Grotle evolves at level 32
I think a Grotle evolves around lv. 35. I never really trained a Grotle, but I know it's evolution level is the same as the other starters. Or around that.
Turtwig evolves into Grotle at level 18, then Grotle evolves into Torterra at level 32.
Turtwig evolves at level 18 into Grotle. Then Grotle evolves at level 32 into Torterra.
Turtwig evolves INTO Grotle at Level 18Grotle evloves INTO Torterra at Level 32
Level 33 and up on Pokemon battle arena
grotle learns mega drain at level 27
Level 18 = Grotle Level 32 = Torterra