This is the flower of Trachelium caeruleum which blooms most of the summer through November.
The flowers are tiny in dense clusters shaped like umbels
The common name is Throat Wort because a medicine is made from it to treat some kind of throat problems.
The flowers are quite profuse and beautiful.
Trachelium grows to about 18″ – 24″ tall. At Dawn Gardens it gets no water; I never put emitters on them. They may get some water from emitters of adjacent plants.
The brown seed heads come after the flowers and many times you can have seed heads and flowers at the same time.
This plant blooms so profusely that it will produce new flowers under the seed heads whether the flowers are dead headed or not.