The nature needs to be something that doesn't hate dry Pokeblocks. Mild, Modest, Quiet, Rash are the best options as they love dry blocks. You don't want to use the low level berries such as Chesto, Oran, Lum, Bluk, and Weaper. They are the right color, but the level is so low that they won't help. Wiki, Kelpsy, Hondew, Cornn are all better choices. If you can spare a Pomtre berry, it's the best choice. As long as you don't use a bad nature or low level berries, it will evolve.