I have had White Diamonds for 3 years now. It blooms fine. My problem is that it is what I call "no color". I have read several sources about them,as well as the tag that came on it, and they all say they are prized for being white and holding their color longer than other white ones. Well, mine start out white, but VERY quickly change to this strange green color. NOT a lime green like Limelight, not attractive. It just makes the blooms invisible. They are the color of the foliage and stay that way till they turn the papery brown in fall.
My research said they are not affected by soil PH,etc. It is on the east wall of my house so it gets protected from the very hottest evening southern sun .
Hi, corgimom. Hydrangea blooms mature and age after a few weeks. The exact number of weeks depends on the variety. I do not have paniculatas to compare against. The only whites that I have are Annabelle and its blooms turned green already so I do not remember how long they were white. Mme Emile Mouillere is another white that I have but its blooms already browned out due to the huge drought that we have. So I am not sure how long those stay white either. I would expect them to be white for 3-4 weeks though. The information that I found on WD does not highlight holding the color longer. Instead, they mention that it was developed to breed a more compact shrub than its parent, PeeGee. I suspect they used commercial phraseology like "longer than most" when talking about that.
Let me then suggest placing it in another location where it gets less sun. The reason for that is Limelight. Limelight blooms start green and stay green for a while. Planting Limelight in a sunny location makes the green blooms age faster so they turn white quicker than if planted it in more shade. Perhaps planting WD where it gets less sun during the summer will help you. For example, if it gets sun thru 2pm, is there a spot where it can get sun thru 11am-12pm?
Note: I do not recommend transplanting during this drought!