I agree, more sun helps ensure better flower production as long as it is not extremely harsh summer sun that all hydrangeas cannot handle. You start having severe issues with no direct sun or so. For the PGs, perhaps consider April as a fluctuating flower bud developing date where, in some years, the shrub is developing flower buds by then and in other years, it may develop flower buds slightly later? Panicles and smooth hydrangeas develop the buds somewhere mid spring but depending on variety some may develop flower buds later too. There may be a remote chance that they can develop flower buds and still bloom unusually late but, I saw that happen only in areas with a long growing season in Georgia. Hope the deer do not try to "test" your fence. ;o)

My tree hydrangeas are reliable bloomers. My yard is shady and I have one in bloom in a very shady spot. They even did well last year, when even my forsythia failed. My blue, shrub hydrangeas are quite variable. This year, I'm getting quite a show.

I'm outside of Portland, now 6A.

I have a similar issue with my shrub hydrangeas (pink/blue head). I think they are macrophylla and one is called Endless Summer.

They simply don't bloom enough and have stayed relatively small. One of them is in its third year, the other the second year, and a third I transplanted from a woody place.

I fertilized with Holly-tone as prescribed in early spring but they barely do anything. Is there something I can do to stimulate more growth but especially bloom?

They get plenty of sun, the first two perhaps a bit too much - the leaves may scorch a bit in the afternoon sun.

Which of the 6 varieties of the Endless Summer Collection? When I lived in Atlanta, wildly fluctuating temperatures tended to kill the flower buds of winter tender Big Leaf Hydrangeas. It may be necessary to protect the shrubs by watering deeply the night before, maintaining 3 to 4 inches of organic mulch and covering with sheets/frost cloth/burlap or by winter protecting from your city's average date of first frost through your average date of last frost. Also consider fertilizing by or after your city's average date of last frost. And applying the last fertilizer application 3 months before your average date of first frost, not later. Since they can develop flower buds as far back as last summer/fall, I assume you rarely prune and wait to remove leafless stems by the end of May or so, not before. These shrubs will first have new stem growth from the crown/base of the stems by themselves and a very long time later, the leafless live stems break dormancy, leaf out and bloom so premature pruning can cut off some potential blooms as the stems appear dead but may be alive..