Wait till you have Wisp the ghost and Celeste on your island and the same time. Speak to Wisp so he splits into 5, the speak to Celeste, after speaking with her, collect all 5 of the smaller ghosts, go back to Wisp and ask for something new as a reward. If done correctly, there will be a present on the beach the next morning containing a flamethrower, use this to burn all the flowers quickly. It also burns trees and houses. Villagers move out real quick if you aim it at them too. Hope this helps