Mushroom plug spawn, also referred to as dowel spawn, are hardwood dowels inoculated with mushroom mycelium. Mushroom plugs are most commonly used to inoculate hardwood logs and stumps in an outdoor growing environment. In most cases, mushroom plugs are used to grow Shiitake mushrooms, but plug spawn is also a great way to grow other types of mushrooms, such as Reishi, Lion’s Mane, Oysters, and more.