First of all, iloveflareon123:
You would have to get a Ditto and breed your Torterra with it to get Seed Bomb.
That's not how breeding works. (Actually I might get what you mean but this could be misinterpreted.) Also it's impossible to get Ditto until the post-game.
Second of all, it does make some difference which Gen 4 game this is, because a tutor exists for it in Platinum, but at the same time, you also can't get it until you reach the Survival Area, which is in the post-game. So, it may be inaccurate to say the only way to get Seed Bomb on it is through breeding, but if you want it before the Elite Four are defeated, you'd have to train an entire new Torterra.
Third, you'd be shocked how many Pokemon that aren't grass types get Seed Bomb, you shouldn't assume that the next one would be a grass type.
It doesn't suck enough that you should immediately exclude consideration of its use. Yes, other than Seed Bomb, Wood Hammer is your only other physical option, but I actually highly encourage it - don't be afraid of it, it's worth the recoil. I don't know why people are so afraid of it.