From Bulbapedia, the community-driven Pokémon encyclopedia.
Potpourri Island (Japanese: ポプリ島 Potpourri Island) is an anime-exclusive location in Kanto. Ash, accompanied by his friends, reached Potpourri Island after defeating Pike Queen Lucy at the Battle Pike and earning the Luck Symbol. It's not too far away from Fuchsia City. There is a town on one side of the island, called Wisteria Town.
This island was shown in Off the Unbeaten Path. Ash with Pikachu, May with Eevee, Brock with Bonsly, Max with Munchlax, Jessie with Meowth dressed as a Sneasel and James with Mime Jr. participated in the Pokémon Orienteering contest which was being held here. James managed to win the contest and earn the prize, which he gave away to Ash and friends, much to the bewilderment of his Team Rocket colleagues Jessie and Meowth.
In the next episode, Ash and his friends traveled to the other side of the island, to Wisteria Town. A Contest was held here and May wanted to enter. Harley entered too, however and he managed to defeat May in the final.
Pokémon seen on Potpourri Island
A potpourri is a mixture of dried plants, usually ones that are associated with pleasant fragrances. They are commonly used as air fresheners for domestic purposes.