you can't. you have to get gloom and give it a sun stone.
Catch a Gloom, then give it a Sunstone.
you can't catch it. evolve it from the Pokemon after oddish with a leaf Stone
You can't catch Rotom in heartgold.
you cant catch him in heartgold you can only get him in soulsilver
In HeartGold you can catch Kyogre.
Raise an oddish to evolve to gloom, or catch a gloom in the safari zone, then evolve it with a sun stone. You should get bellossom.
You can only catch Vulpix in SoulSilver, not in HeartGold. You can catch it on route 36 and route 37.
In pokemon Heartgold
No
you cant catch it it is rare
Bellossom is a Grass type pokemon.
You can catch Lombre in Pokemon HeartGold in the Safari Zone at a waterside area once you receive the National Pokedex.