no you can't, im sorry
You can't get to Johto region in Pokemon Diamond/ Pearl, but you start there in Heartgold/ Soulsilver.
You can only have Pokemon from Hoenn to Jhoto ONLY if you trade them.
JHOTO
You can go to a potion of the Jhoto Region in the Jhoto Safari Zone,after you beat the Elite Four and Champion.You can encounter Jhoto Pokemon in the Jhoto Pokemon.And Oddish aren't in that part of the Safari Zone to annoy you.However....try using HM's on the tree's...
NO. You cannot. It was rumored and things like this are always rumored. You CANNOT go to jhoto or hoenn or Kanto. You are stuck in SINNOH. Though Pokemon Heart Gold and Soul Silver will be located in jhoto and will be available on the Nintendo DS.
No. Johto is not an available region in Pokemon FireRed. You can only explore the region of Kanto and the nine islands surrounding it. Currently, only Pokemon Gold, Silver and Crystal are games which explore Johto.
I personally believe its Lugia.
'in the norhtern mtns.
you have to complete the sinnoh dex then go to the pal park,in the grass!
14. 8 in the Jhoto region & 8 in the Kanto region
Complete the national Dex with Jhoto region Pokemon wait a few Seconds,Minutes,Hours,days, or weeks then select the three jhoto starter Pokemon
This website shows all sinnoh Pokemon, all though diamond has some kanto, jhoto and hoenn region Pokemon thrown in for good measure however tese are not shown on this website http://Pokemon.marriland.com/diamond_pearl/pokedex