u know how bulbasaur is supposed to learn leech seed at level 13. mine never learned it. can someone help me please.

Bulbasaur learn Leech Seed at L7. It's Vine Whip that happens at 13.

The growth schedule that Bulbasaur uses starts out gaining levels very fast. It only needs 236 EXP for level 7, and 314 for level 8. If it has 235, then gains 79 in a single battle, then it skips directly to level 8 without ever touching 7, and as a result it will never learn Leech Seed. The only way to get the move back involves importing it into a Stadium 2 team that can beat the E5, but you'll need to progress a lot further in the game to get Pokemon capable of doing that, and by that time you probably won't want Leech Seed anyway.

I always wondered why bulbasaurs grow so fast..