Michael Denny’s peony bloom date chart lists Dr. John L. Crenshaw as blooming 39 days after Red Charm.  It’s got to be a very obscure and hard peony to find, though. Elsa Sass is listed as only 15 days later than Red Charm, and Ann Cousins only 17 days later.

I am growing Lord Cavin (19 days) and Candy Stripe (20 days). They are new in my garden and I know nothing about the fertility of Lord Cavin, but Candy Stripe is recorded as the seed parent of at least one hybrid.  Jappensha Ikku is one of my later blooming peonies and has produced seed, and I’m pretty sure it has also pollinated other peonies. It is listed as a “mid season” bloomer but not in my experience.  It isn’t on the list. The list is not all that up to date, nor could possibly have every peony. Still, I would recommend checking the list for potential varieties.

http://peonybloomdate.com/data.htm

Thank you for starting this thread and for the great information about varieties, and the peony bloom date chart! I didn´t see this until now, so I already wrote a similar question in the hybridizers group. Sorry for that 🙂

Took a look at the blooming chart and these seem to be the latest according to that chart:

John L. Crenshaw  (39 days)

Golden Dawn (36 days)

Charles McKellip (32 days)

Red Satin (25 days)

Polly Sharp (25)

Fantastic (25)

Avalon (25) (fertile)

The problem is that  I  can´t find any of them, except for Red Satin, in Europe. I found seeds from Polly Sharp on the seed list from the American Peony Society though. I´m not a member unfortunately so I can´t search their member area for entries about these varieties. 🙁