I planted three ‘Blue Muffin’ viburnums (Viburnum dentatum) four years ago because I wanted berries for birds, but they have never produced any berries here in Pa. (Zone 6b). I planted them in front of a ‘Chicago Lustre’ viburnum (another cultivar of viburnum dentatum) because multiple sources said they would cross-pollinate. The Blue Muffins always are finished flowering by the time the Chicago Lustre flowers, however. Thus, no cross-pollination and no berries on the Blue Muffins. The two Chicago Lustre’s that I have in my yard both produce berries every year, however, and I’m puzzled as to what’s cross-pollinating with them. I have other native viburnums in my yard, but no other cultivars of dentatum. So does anyone have success with getting Blue Muffins to produce berries? What can I do to duplicate your success?