When I got to Violet City I decided to train past the city gates so I talked to some people and they kept talking about some "wiggly tree" and I said to myself "It's got to be a Sudowoodo" so I walked up clicked it for a capture attempt but it just wiggled so I tried again and again but zero so I came back after beating Falkner and tried having my Chikorita use Flash but nothing so I tried having Chikorita use Cut after besting Bugsy so I ask how do you uproot it?
I do play HGSS, but I think this includes crystal:
You need a SqirtBottle - an item a girl in Goldenrod's flower shop gives you.
Once you have it, say yes to " sprinkle water on tree ".
Sudowoodo should appear for battle.
Hope this helps:)