[From Landscaping with Antique Roses, by Liz Druitt and Michael Shoup, p. 109:] Once-blooming roses make up for their shorter season by putting all their energy into one overwhelming display.
[From Climbing Roses, by Stephen Scanniello, p. 2:] Most species roses (roses that occur naturally in the wild and are commonly called "wild roses") and almost all the old European garden roses flower only once a year, in the spring or early summer.