From Bulbapedia, the community-driven Pokémon encyclopedia.
The Xanadu Nursery (Japanese: ムラサメ植物園 Murasame Botanical Garden) is an anime-exclusive location found in the Kanto region. It is located near Pallet Town.
The nursery is a large greenhouse that is home to various flowers and plants. Among them is a flower that contains Stun Spore. Two of the nursery's employees are Florinda Showers and Potter. Along with Florinda's Gloom, they help to make sure the operations at Xanadu run smoothly.
While training for the Pokémon League in Make Room for Gloom, Ash's mom requested that her son help her run some errands and visit the nursery. Ash and his friends took off, not wanting to help with Delia's plans. Eventually, they ended up at the very place she requested them to be.
Ash told the others that he used to visit the Xanadu Nursery when he was younger, but hadn't visited it in a while.
Kublai Khan's summer capital, both the real life version and the fictional version found in the poem Kubla Khan, were both named Xanadu; both were known for their vast and beautiful gardens.