The plant size and habit of Old Garden Roses and Shrub Roses differ from those of Hybrid Teas, Floribundas, and other roses with the China Rose predominant in their ancestry. Old Garden Roses and Shrub Roses are true shrubs, typically larger and much more branched in crown architecture.
Among the Old Garden Roses, Albas are the largest specimens, usually 6 feet or greater in height. At the other extreme are the Gallicas, typically 4 feet or shorter and very upright in habit. In between are the Centifolias and Damasks, both of which are more lax in form, and the Moss Roses, more upright in form.
Size is more variable among the rose species and Shrub Rose cultivars. Most plants fall between 3 and 6 feet in height. Some of the tallest plants are found among the Hybrid Spinosissimas, Kordesiis, Shrubs, and Species, with heights ranging up to 12 feet.
Winter injury has a major impact on plant size among roses at the Minnesota Landscape Arboretum. Mature heights are often less than those published in descriptive texts. Most affected are the taller cultivars that lack cane hardiness and commonly die back to the snowline. Even when regrowth is vigorous, many of these plants fail to reach their mature height during the following growing season.
Lower-growing cultivars, such as the Gallicas, with mature heights of 3 to 4 feet, are not as affected by winter injury. A smaller proportion of their crowns are winter-injured and these cultivars can easily regrow to their mature heights the following growing season.
Snowcover affects rose size and habit in two ways. It is a natural insulator of rose canes, serving to minimize dieback from low winter temperatures. A heavy snow can also weigh canes down, resulting in a wider, flatter plant habit the following growing season.
Descriptors for Growth Habits of Rose Cultivars
arching. . . Growth is similar to the “spreading” form but cane tips bend back towards the ground.
climbing. . . These cultivars produce long canes that, when tied or supported, will climb indefinitely. If not supported, these plants take on a wide arching habit.
dense. . . Many upright canes create an erect dense plant habit.
groundcover. . . Canes grow horizontally over the ground’s surface.
open. . . Upright canes create an erect plant similar to the “dense” form, except that the number of canes is fewer, resulting is an open, airier habit.
rugosa. . . This form is typified by frequent branching of canes and short internodes. Without foliage these plants look very “twiggy.” Many Hybrid Rugosas exhibit this plant form.
spreading. . . These plants are V-shaped. Cane growth is angled instead of vertical.
suckering. . . This is similar to the “dense” form except that suckering can occur. Many Gallica cultivars exhibit this form. Unless controlled, suckering can increase plant width. Some cultivars sucker so vigorously that invasiveness is a problem.
A rose plant’s width is most often affected by a cultivar’s ability to sucker. Suckering is common among Old Garden Roses and Species Roses.
Most rose cultivars are propagated by budding. Because the bud union is susceptible to winter injury, plants in northern climates should be planted with the bud union 2 to 4 inches below ground to protect the union from injury. This often results in the formation of roots by the cultivar above the bud union so that plants go “own-root” over time, and suckering can become a problem. Unless controlled, roses prone to suckering will continue to increase in width and invade the space occupied by neighboring plants.
Kordesiis commonly produce extremely long canes in a short period of time and are often trained as climbing roses. In Minnesota, inadequate cane hardiness prevents most of these roses from being used as climbers. Instead, they are grown as shrubs with long, arching canes. Because of their rampant cane growth, they measure among some of the widest cultivars.
Plant size and form are described in Table 7. The heights and widths listed are the maximum sizes that were seen at the Arboretum between 1989 and 1992. Eight terms were used to describe plant form for each cultivar or species: arching, climbing, dense, groundcover, open, rugosa, spreading or suckering.
|Andersonii has beautiful, glistening pink, single flowers which bloom on previous year’s wood. Its canes are not hardy and need winter protection for flowering to occur.||‘Marguerite Hilling’is a pink sport or mutation of ‘Nevada’. The cultivars are identical except for flower color. A branch of this ‘Marguerite Hilling’ is reverting to the white-flowered ‘Nevada’.||'Alika', like most Gallicas, suckers. The clumps seen here were originally a single plant. Flowers are deep pink, semi-double, and very fragrant.|
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