20 YEARS!?!?!?! No blooms at all? Is it planted out of zone? What variety of hydrangea is this? Do you know the name?

Is it a macrophylla hydrangea? Your zone is cold enough that the buds may be freezing--or late-spring warm-up periods alternating with late-freezes may be taking those buds. I'm assuming you are about in Zone 6. Macrophylla hydrangeas often don't bloom well in Zone 6--I no longer even try to get them to bloom. My neighbor must have about 6-8 of them--they have never bloomed in the 6-8 years she has had them. We are in Zone 6 also.

What I do instead is plant Annabelle hydrangea in semi-shady spots and some paniculata hydrangeas (like Pinky Winky) in sunshiny spots. They are all surefire--you'd have no problem with them not blooming.

Kate