In the pursuit of elegant flowers, it was almost inevitable that rose breeders would combine the hardy, free-flowering floribundas with the magnificently large-flowered, long-stemmed hybrid teas. In so doing, they created the Queen Elizabeth rose, which was introduced commercially in the United States in 1954 and became the basis for the newest type of rose, the grandiflora. (In Great Britain, grandifloras are considered a subclass of the floribunda and are called floribundas, hybrid-tea type.)
Grandifloras combine their parents' best qualities in hardiness and blooming habit, and flower continuously except for a brief midwinter dormancy in Zones 9 and 10, and from early summer to frost in Zones 3-8. They bear great quantities of blossoms that are 3 to 5 inches in diameter--slightly smaller than most hybrid teas, slightly larger than floribundas. The blossoms are double, with as many as 60 petals, and may appear one to a stem or in candelabra-like clusters on a bush; the stems of grandifloras are longer than those of floribundas. The buds and blossoms, as well as foliage and thorns, resemble those of hybrid teas. The grandifloras have a color range that is much the same as that of their parents: from white, pink, yellow and orange to dark red, but with no lavenders and few mixed colors. Oddly enough, while the blossom size and stem length of grandifloras are compromises between those of hybrid teas and floribundas, the height of grandifloras often outstrips that of both of their parents, and most varieties usually grow 3 to 6 or more feet high. This stature makes the flowers ideal for use toward the back of a rose bed. Grandifloras also serve as lovely informal hedges and screens. And since even their clusters have long stems, all grandifloras are suitable for cutting.
Courtesy of Time Life Plant Encyclopeadia