Whomping Willow

• Type: Magical Flora
• Location: Hogwarts Grounds
• Owner/Residents: Hogwarts School of Witchcraft and Wizardry
• Key Features: A highly aggressive, sentient tree that attacks any object or person within range of its branches. It possesses a secret mechanism for pacification.

The Whomping Willow is a very large, valuable, and uniquely violent species of magical tree located on the grounds of Hogwarts. Its branches function as limbs and will thrash and “whomp” at any perceived threat that approaches its trunk. The tree's violent behavior is its primary defense mechanism and a deliberate feature intended to guard a secret. The tree was planted on the Hogwarts grounds circa 1971, the same year that the werewolf Remus Lupin began his education at the school. Albus Dumbledore had the tree placed directly over the entrance to a secret tunnel leading from Hogwarts to the Shrieking Shack in the nearby village of Hogsmeade. This was done to provide Lupin with a secure and secluded location for his monthly transformations, protecting him and other students from harm. Each month, Madam Pomfrey would escort Lupin to the tree. Despite its violent nature, the Whomping Willow can be temporarily immobilized. A small, specific knot at the base of its trunk, when pressed with a long stick or branch, causes the entire tree to freeze, allowing safe passage into the tunnel beneath its roots.

The Whomping Willow plays a significant role in several key events throughout the series.

• In Harry Potter and the Chamber of Secrets, Harry Potter and Ron Weasley crash the flying Ford Anglia into the tree upon their late arrival to Hogwarts. The tree retaliates, severely damaging the car, breaking Ron's wand, and ejecting the two boys and their luggage. The incident earns them detention and leads Professor Sprout to bandage the tree's injuries.
• In Harry Potter and the Prisoner of Azkaban, the tree is central to the plot. After being mistaken for the Grim, Sirius Black in his Animagus dog form drags Ron Weasley into the secret passage beneath the tree, breaking Ron's leg in the process. Crookshanks, having befriended Sirius, knew how to press the knot to immobilize the tree, allowing Harry and Hermione Granger to follow. It is within the Shrieking Shack at the end of this passage that the truth about Sirius Black, Peter Pettigrew, and Remus Lupin's past is revealed. Lupin explains the tree's origin and purpose to the trio.
• In Harry Potter and the Deathly Hallows, Harry, Ron, and Hermione use the secret passage under the Whomping Willow to enter the Shrieking Shack during the Battle of Hogwarts. They do so in order to reach Lord Voldemort, who is using the shack as his temporary headquarters. From the tunnel's entrance, they witness Voldemort murder Severus Snape.

• Secret Passage: The primary reason for the tree's existence is to guard a long, earthen tunnel. This passage begins in a hollow beneath the tree's roots and emerges through a trapdoor in the floor of the Shrieking Shack.

• J.K. Rowling revealed that the Whomping Willow was planted to protect Remus Lupin, noting that it was part of a larger effort by Dumbledore to make the school inclusive and safe for a student with lycanthropy. (Pottermore)
• In the film adaptation of Harry Potter and the Prisoner of Azkaban, the tree is depicted as significantly more active and malevolent in its attempts to attack the trio. It captures not only Ron (who is dragged by Sirius) but also grabs Hermione and flings both her and Harry around before they can enter the passage. This is a departure from the book, where only Ron is seized by Sirius. (film)
• Students at Hogwarts apparently used to try and touch the trunk of the tree as a dare. One student, Davey Gudgeon, nearly lost an eye attempting it.