Well...first you surf at Jubilife city(the dock to the left) to get to canalive city then go across the bridge in the middle. On the other side the gym and a boat will be there. Talk to the man by the boat and say yes to him. You will go to a place called Iron Island. At the end of the island there will be a item, the shiny stone! Pick it up and give it to your roselia and ka-boom! Roserade!
Yes with a shiny stone.
Use a shiny stone
Give it a shiny stone and it shld evolve. .
Find a shiny stone
You have to find a shiny stone (which are found on iron island b3f or on route 228)
Beat the elite 4 and go to route 228 and find some kind of stone.
Using a leaf stone
You either use a leaf stone or wait till it gets to level 36 so it evolves on its own.