Cross posted in the tree forum since it's unclear as to what to classify this...we consider it a tree but I often see it referred to as a shrub.

We planted a Seven Sons Flower about 4 years ago. It's about 8-10' now and very healthy in every way EXCEPT we haven't had the beautiful display of pink calyx. We do have alkaline soil and they do like acid but since it looks healthy in every other way, I'd think we would have seen a full display of pink calyx. Last year I did see about 3 of them and thought that would be the year. Sadly that was it. Does this tree take years to have this happen or is there something else going on? If it was struggling, I'd think it needed something, but it actually looks healthier than most that I have seen in the pictures online.

I have a European Mountain Ash that for the 1st two years I had flowering and then for the next 4 nothing. It looked extremely healthy but nothing. Then this year it flowered beautifully and now has the berries. This tree too prefers acid soil (yes, I know I'm pushing my limits but there are so few trees that I like that like alkaline soil). Could my Seven Sons Flower just need more time?