Nope.
well, it does exist...but not particuly how you would expect. its kind of like glitch city, but its got bill in it. ive gone there. but yes, it was a hoax calling it the secret garden. its just a screwed up place with bill in the middle
That's not the secret garden. There actually is a secret garden, but it doesn't have anything interesting. You have to use a glitch to get there.
HOW TO GET TO BILL'S BORINGLY SECRET GARDEN
Requirements:
A Pokemon that knows SURF
A Pokemon that knows FLY or TELEPORT (to get out, because otherwise, there's no way to get back in the regular game!)
Steps:
1. Go to Bill's house at the cove, but don't go in.
2. Go to one place that has SURFable water up from you, and the barrels on the other side (By barrels, I mean the things that keep you from going out of bounds)
3. Walk towards the water, and you should hear the can't go there sound. Keep doing that, and without letting go of the button, press the START button.
4. Save and reset your GameBoy or VBA.
5. Once you start playing again, your character should be facing the water instead of the classic down.
6. Without moving, press START and start SURFing. It should surf down, right onto the barrel!
7. Keep SURFing, and go to the land next to Bill's house. That's Bill's Boringly Secret Garden. To get out, use FLY, TELEPORT, or reset the game.
There. That's my explanation of Bill's Secret Garden.