The new and distinct hybrid of Hardy Geranium plant named Geranium ‘；Boom Chocolatta’； with large, rounded, deeply-cleft, palmately-lobed foliage having dark bronze color. Numerous, densely-branched, erect, stems display blue-purple flowers above the foliage beginning early summer for about three weeks. The new plant is vigorous and produces large, upright, winter-hardy mounds.
