Perhaps Spiraea thunbergii.

Here is a link that might be useful: Spiraea thunbergii

I second S thunbergii, narrow long leaves and flowers point very much to that species

(it flowers early in the season, after Forsythia?)

looks somewhat starved
hates root competition according to my "The-best-nursery-catalog" by some German tree person

Thanks, I'm sure that is what it is. I see where it has been called baby's breath. This one just came up where it is.