The Sacred Sprout (also called the Sacred Bud) is a magical plant introduced in Season 4.
The Sacred Sprout acts as both the source of magic to Diana, Major Fairy of Nature, as well as the source of the Earth's wild natural energy. With it, Diana commands total control over the planet's natural life (mainly the plant and animal life). Also, according to legends passed down by a tribe of people native to Amazonia, destroying the Sacred Bud can result in Diana's demise but doing so may very well cause the planet's nature to die alongside her.
As such a crucial item to Diana, the Sacred Sprout is hidden within the Nymph Waterfalls which are located within the deepest part of Amazonia, Diana's kingdom, where she and her followers, the Amazon Fairies, may guard it from those harboring malicious intent.