One two things , the Goldstrum needs stratified outside just like the Echinacea Purpurea , When doing them (growing for yourself) take a seed head , let dry a few weeks , turn upside down in the ground or large pot that holds moisture well , outside , all winter ,(stratification required)
While dormant or at first sprout in spring , best time to move them ,( Larger plants) old plants)
Deadheading can extend bloom time but not much if any for me ,
Hope this helps
oops I have White Swan , Don't know about Pow Wow But neither of these require stratification or so I hear , I stratify mine (White Swan) Anyway
