If you're talking about the tree that blocks the other Route. You'll need the Squirtbottle. Then go back and spray the tree and it would turn out to be Sudowoodo. I don't think it is that tough to beat or to catch. Make sure you have some Great Balls at least and some water Pokemon with weak Water type moves and it'll eventually get low health.
beat goldenrod gym and then go to the flower shop and get the squirtbottle and thn spray it on the sudowoodo and you can battle it.
breed sudowoodo dufis :P
Breed a sudowoodo holding a certain incense
sudowoodo
Sudowoodo
The Pokemon bocking your way is a Sudowoodo. To battle the Sudowoodo, you must use the Squirt Bottle on it.
if you know the sudowoodo blocking the way u have to battle it and catch it
sudowoodo and smeargle
I don't think you can battle Gardenia in Pokemon HeartGold.
In Pokémon HeartGold and SoulSilver, you first have to defeat Whitney (the Goldenrod Gym Leader) in a Gym Battle. Next head to the Flower Shop in Goldenrod City and talk to the lady there. She'll give you a SquirtBottle. Take it to the Sudowoodo and use the SquirtBottle on it. It'll challenge you to a battle. Defeat it or catch it and it'll be gone.
Sudowoodo can be found after you defeat the elite four. Sudowoodo is located at south-eastern area of the Battle Frontier.
at the battle frontier there is only smeragle 40-50 and a sudowoodo on 50 actually sudowoodo is lvl 40 at the battle frontier