Newly Carolina Cherry Laurel Tree Branches Are Breaking Hanging And Dying

Question From: CALIFORNIA
Q: Why are newly planted prunus caroliniana bright and tight branches with good greenery breaking off and hanging vertically until leaves shortly die and branch either falls off or is gently pulled off. Trees otherwise look healthy (green leaves and upward growth) but are growing scraggly due to branches going away daily.

My guess is extreme heat and  lack of water.
Best Nancy