I'm a bit puzzled by your question. If you're planting rudbeckia now (which variety by the way), you should be dealing with growing plants, not dormant plants. Are you saying your plants die after you transplant them or do you always get them before they've sprouted (very early spring)or very late fall after they've gone dormant (I guess) although my rudbeckia keep their leaves through winter. Maybe other varieties don't. No clue.

Some are annuals, some biennials, some perennials, so it's kind of important to know which ones you've been dealing with. I'm not sure of this, but in my experience and in my zone rudbeckia seem to do better transplanted in spring. The ones I've tried to move in the fall (mainly Goldstrum) never make it through the winter.

Kevin

I was a little surprised to see that Swallowtail Garden Seeds classifies all Rudbeckia seed types as annuals. I know from experience they self-seed but evidently that's how they give the impression they're perennials. I've been yanking seedlings from the neighbor's lawn and they didn't plant Rudbeckia...I did!

The site is sunny, average-good moisture, soil is alkaline but good.

The soil here is acid and where I have Rudbeckia growing, it's nothing more than sand & rocks. They get full sun but they're on their own as far as nutrients & supplemental water. It's just a guess but maybe your soil is too good for them. I find they do best here if they are growing in the worst soil & get no care whatsoever, including water above & beyond what Mother Nature provides. That being said, I noticed they were just as happy this year with plenty of frequent rain as they were last year when we had 4 months of drought from June to October.

I should qualify these comments and state my plants were winter sown from seeds, not grown from nursery stock. Health & endurance-wise, winter sown plants are giant steps ahead of nursery-grown plants.