This cultivar which is a hybrid of H. nigrescens was originated by Ken Herrema of Michigan and registered on his behalf by Peter Ruh in 2000. The giant size plant grows to about 30 inches in height with a spread of 72 inches. Its upright mound of blue-green foliage turns to medium green later in the season. The leaves are slightly wavy, slightly corrugated and deeply lobed at the base with a distinct tip. Its lavender flowers bloom in July.

According to The Hostapedia by Mark Zilis (2009), "Whenever I've seen this plant in Peter Ruh's collection, one word comes to mind: elegant...it more closely resembles Hosta fluctuans in overall appearance.

An article about H. 'Allegan Fog' by Warren I. Pollock in The Hosta Journal (2002 Vol. 33 No. 2) states that, "This hosta is an introduction of Ken Herrema of Englerth Nursery in Hopkins, Michigan. 'Allegan Fog' is named after Allegan County where this nursery is located. Other hostas from this nursery, started by the late Larry Englerth, also have Allegan in their names. In 2000, Peter Ruh...registered three hostas for Ken Herrema: 'Allegan Fog', 'Allegan Emperor' and 'Allegan Gent'."