I have some Black Eyed Susans (Rudbeckia Goldsturm) and Coneflower (Echinacea purpurea & powwow wild berry) that have been so easy-care, that I haven't really done anything to them for the last 2-3 years except fertilize and water. Which is a good thing, but I think they could be better. I'd like to get some answers on a few things from those who are more experienced. Any advice is welcomed.

When is the best time to cut the flowers back? I've heard this will extend the bloom season. Is that true?

If I want to share these plants, when is the best time to dig/transplant?

Last year I tried collecting the black eyed susan seeds. I shook the brown flower remnants into a paper bag, dried and refrigerated the seeds. I planted in a warm window in early spring in a seedling mix (the same I use for my daylilies). I added a little hydrogen peroxide to my water to prevent damping off, but none of my seeds sprouted. What am I doing wrong?

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

Deadheading helps with Echinacea but I have not noticed much of a difference with Rudbeckia. Echinacea do not really like a lot of fertilizer , most years I only give a bit of bone meal. I would divide or transplant in the Spring , they take longer then others to establish. I almost never plant one after mid July because survival rates are low after that.

I have moved both in August and very early September and had them do fine the next year here in zone 5b. Our first frost is typically around the middle of October. I like to make sure things have time to get rooted and settled in. In Georgia you could maybe push into September easily. I have also moved them in early spring with success,