Yes and no.
If you do not complete the storyline of Pokémon Black and White, you will not be able to get Turtwig.
You may be thinking, "I could just trade Turtwig over from Pokémon Diamond, Pearl, or Platinum". No. The games won't allow Pokémon from other games to enter that single game. Of course, you can trade between the two games (Black and White).
After you complete the main storyline (after you beat the Elite Four and a couple of other people… I'm not gonna spoil it), a lot of other Pokémon will appear. The main place to find new Pokémon is in the new routes, White Forest (Pokémon White - Wild Pokémon) or Black City (Pokémon Black - Trainer Battles), and "Swarm Pokémon", which you can find out the route on the electric bulletin boards.
If you were talking about the anime, then no.
You cannot capture Turtwig in Pokémon Black 2 so the only way to get it in Black 2 is via trading.
You can't catch a turtwig, you can only get it through a pokemon dream world event
A girl torterra and a boy same Pokemon/type.
Turtwig (grass) Chimchar (fire) Piplup (water)
You either have to trade with someone who has one or transfer it in from a Gen IV game.
NO
You tansfer it from earlier generation games
The only ways to get Torterra or even its first form of Turtwig in Pokémon Black and White is through transferring it from a previous game, trading for it or via a cheating device.
You cannot capture Turtwig in Pokémon Black 2 so the only way to get it in Black 2 is via trading.
Turtwig is a Grass type pokemon.
You can not get a Turtwig egg in Pokemon Platinum. But if you breed a Turtwig with a Ditto, then it is possible.
You can't catch a turtwig, you can only get it through a pokemon dream world event
A girl torterra and a boy same Pokemon/type.
well, you cant actually catch turtwig in Pokemon black because it is one of the uncathchable Pokemon because it is Pokemon diamond and pearls starter for the grass type.the only possible way is to use poke transfer[located near marvelous bridge] on your Pokemon black game if you still have your instruction booklet, that helps.
Breeding Turtwig with another compatible Pokemon.
at the begining of the game the profeser will give you three Pokemon and you have to pick one and those three Pokemon are turtwig chimchar and piplup and if you want turtwig pick turtwig.
Yes you can. Turtwig is a starter pokemon, just like Pokemon Diamond or Pearl.