'Prairie Sun' is a Rudbeckia hirta cultivar. My books say that R. hirta is a biennial, or short-lived perennial. It appears to be best treated as an annual, judging from the way it's cited on internet sites.

Hi - I had it winter over two years ago and it was absolutely wonderful, huge, tall, profilic plants! But, this winter it did not! So, I've replanted and will definitely mulch this year (which is what I did the first year I had them). Indian Summer also didn't winter over, but the plants that were planted as new last year did! The herbstonne and green wizard perennials, did! So, I wish we had hardier varieties...
Wendy

R. hirta 'Burpeei' is a great flower. It bloomed like mad in it's first year, from winter sown seed, and it came back with a much increased footprint (and a bunch of volunteers), and blooming just as vigorously as last year. It has a very thick stem, and does fairly well in plain old water. I haven't tried any kind of conditioner yet. Burpee says its hardy to zone 4.

This is Burpee's pic:

{{gwi:624611}}

This is mine:

{{gwi:624613}}

Burpee says it has a black eye, mine are noticeably burgundy, and tinges of red radiate about an inch into the petals.

Here is a link that might be useful: R. hirta 'Burpeei'