During my visit last month to the Sarah Duke Gardens http://www.hr.duke.edu/dukegardens/index.html at the campus of Duke University, I was really amazed to still be able to see gorgeous plants and flowers in the middle of October! There are over 55 acres of gardens here - even a section that dedicated soley to the native plants of North Carolina. I can imagine this being a spectacular visit really any time of year - not just spring or summer - as their plantings change with the season.
The gardens are open daily 8am to dusk and some of the gardens are even available for weddings. This was just a wonderful way to spend a fall day and I highly recommend a visit if you are planning a tour of Duke University or the surrounding areas.