Chaste Tree died all the way back to the ground for me here here in 6a. Maybe the radiant heat from the parking lot creates a microclimate for the Vitex at the bank? My soil must not have been acidic enough because it's flowers were more pink than blue. Maybe a half zone can make a difference?

"Under ideal conditions, (Vitex agnus-castus) is hardy to −23 °C (−9 °F) USDA Zone 6. In colder zones, the plant tends to die back to the ground, but as it flowers on new wood, flowering is not affected on vigorous growth in the following season. Cold and wet weather results in dieback and losses. The plant grows well on loamy, neutral to alkaline soil."

Flower color of a chaste tree is not affected by soil pH.

Well thats good to know thanks gardengal. I collected Vitex seeds from a blue flowered plant in Texas, and when the shrub finally bloomed it had pink flowers. I just assumed it was the same ph/color issue that plagues Hydrangea growers. I was 5b but now I'm 6a. I gave up on growing Vitex unfortunately, because it's fragrance is so intoxicating.

I wonder if these are more common in the Midwest? They grow fine around here and I see them very occasionally but not as much as you'd expect...more often in old neighborhoods. I wonder if an old timer like @sam_md knows whether they were once more popular.

Thanks for everyones replies to my question!

I now have another question & included some photos of the original tree I started a rooted cutting from about month ago and when photographing the tree yesterday I found one small seedling that I think is from the Chaste Tree that has serrated leaves.

I understand that the parent plant will not produce seedlings that grow into a special cultivar and that must be done by cuttings.

I wonder where these serrated leaves came from because online I am told that the parent plant for Blue Diddly is Chaste tree (Vitex agnus-castus) and has smooth, lance-shaped leaflets within its palmately compound, hand-shaped leaves, not serrated leaves.

Anyone have any input? I'm only guessing that the mature Chaste Tree is Blue Diddley, maybe I'm wrong about that...also it was covered in gorgeous blue-ish lavender flowers but no photo of that.