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Roses for the North
Plant Size and Habit 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’s Effect on Size and Habit 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.
Plant Width 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.
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