Free flowering, with large pink, double sterile florets, that darken with age to red, or violet or multicoloured on acid soils.  It originated from an open-pollination in 1998 of a unnamed selection of Hydrangea macrophylla, as the female, or seed, parent with an unknown selection of Hydrangea macrophylla, as the male, or pollen, parent. The cultivar ‘Shamrock’ was discovered and selected by the Inventor as a single plant within the progeny of the stated open-pollination in a controlled environment in Varengeville Sur Mer,France.

USPatent PP16223, January 31, 2006

Gardens found in 28 pre 2000 surveys DA   MS?

Gardens found in the 10 surveyed in 2010: DA DIN ESV NAN

UK  Plant Finder 2012: Not listed. (waysidegardencentre.com) 2009