Mountain Ash, also known as Sorbus americana, is a form of ash created by burning the wood from a Rowan tree, which possesses the ability to protect against the supernatural.
Henri Argent had a collection of mountain ash kept in his house, which he used to ward of supernatural creatures such a werewolves when his first wife and four children were killed by the beast of Gevaudan. He created a circle of ash to protect himself and Marie-Jeanne Valet from her brother, The Beast of Gevaudan. They later forged a pike made of mountain ash, steel, her blood and wolfsbane on the night of the full moon, which Marie used to kill Sebastian Valet
When Eichen was built, the doctors at the mental correctional facility had mountain ash wood in the walls of the supernatural wing to keep the supernatural creatures trapped. However the ash was burned away by the hellhounds Cerberus in late 2012.
Sometime before her imprisonment in Eichen and eventual death, Lorraine made sure the boathouse in the Martin family lake house are all lined with Mountain Ash to protect it from supernatural threats.
At some point prior to the start of the series, Alan Deaton used Mountain Ash to fortify the defenses of his animal clinic by replacing his baseboards and the gate between the reception area and the exam room with rowan wood.
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Sometime after Melissa became aware of his werewolf secret in Season 2, Scott had Deaton installed mountain ash into the floorboards. Melissa kept mountain ash in case of an emergency.
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Teen Wolf: The Movie[]
Mr. Harris created a huge circle of mountain ash surrounding the lacrosse stadium to trap the McCall pack as part of his plan with the Nogitsune.
