male plants of Viburnum davidii

I bought 4 Viburnum davidii plants last year and I was assured that one of them was male. Unfortunately, I don’t think that is the case as I didn’t get any blue berries. The plants didn’t flower very abundently – the flowers were small and seemed closed. They are in good soil/dappled shade and seem to be doing well.My question is how do I ensure that I get a male plant and is 1 male to 4 female a good enough ratio to get berries?