It is hard to tell. Most say Mid-late. So what does that mean other than, as you say, they will bloom together depending on their age and condition. I would put that around mid July up here. Fernleaf and Roselette bloom around the end of June (as did my tree peonies which bloomed faithfully June 23-25). So if that is 'early' for me, then allowing for about 7-8 weeks blooming time??? The last to bloom is Garden Treasure. Last bloom died a week ago. So June 23 to July 31 is my bloom period. Ergo, Mid July for med-late blooms.
Who knows. And being first year in the garden next spring you never know. Some do fine, some go the full three years to mature enough to bloom. Also I suspect some of that is due to the stupidity of the gardener who insists on over watering every spring desperately wanting to see something growing besides chickweed. I suspect I have partially rotted perfectly good roots that way. I swear I won't water until the end of May next year. Snow isn't gone til the first of April. Hmmmm. Have to go check.
