Bloom pattern describes the flowering of a rose across the growing season. Differences in bloom pattern among the hardy roses at the Minnesota Landscape Arboretum can be seen between classes as well as between cultivars within a particular class.

Most Species Roses and Old Garden Roses are one-time bloomers in Minnesota, blooming heavily in June on canes produced during previous years. Some of the Old Garden Rose classes, such as the Albas, Centifolias, and Gallicas, are genetically incapable of rebloom. Other classes, such as the Bourbons, Damasks, and Mosses, include some cultivars that have the potential to bloom a second time in late summer or early fall. Rebloom among these classes is inconsistent from year to year at the Minnesota Landscape Arboretum because of the short growing season. 'Salet', a Moss Rose, is the one exception among the Old Garden Roses, blooming lightly but reliably through summer and fall at the Arboretum.

One-Time Bloomers These plants rarely bloom in the year of planting. Beginning in year two, a pattern is established where blooms develop on the tips of previous years' wood as well as on new laterals formed on previous years' wood. Key: green = current year's growth; light brown = one-year-old wood; dark brown = two-year or older wood.
Repeat Bloomers In the summer they are planted, repeat bloomers produce canes that bloom on the tips. New basal canes grow and may bloom at the tips in the first autumn. Additional fall flowers can be produced on laterals formed on the spring canes. During subsequent years, spring flowers are produced at the tips of new canes and on laterals formed on previous years' wood. Fall flowers may be produced at the tips of new summer canes and on laterals formed on spring canes or previous years' wood. Key: light green = new growth in the current season; dark green = oldest growth in the current season; light brown = one-year-old wood; dark brown = two-year or older wood.
	Continuous Bloomers Roses which are continuous bloomers can bloom on cane tips, laterals, or from multi-branched panicles at ends of canes as soon as canes form. There are repeated cycles of cane production followed by flowering through the growing season. Key: light green = new growth in current season; dark green = oldest growth in current season; light brown = one-year-old wood; dark brown = wood two years old or older.

Among the modern roses, some classes include both one-time bloomers and repeat bloomers. There are also classes where all of the representatives found in the Arboretum's garden have some kind of repeat bloom.

Simplifying rebloom patterns of hardy roses into a few single-word descriptions such as "repeat" and "continuous" can be confusing. The value of rebloom depends on the length of the rebloom period and on floral density, which is the number of blooms on a plant at any one time.

Heavy spring bloom is typical of most hardy roses, but flowering during summer and fall is highly variable among the cultivars. At one extreme are cultivars like 'Marguerite Hilling' and 'Nevada', commonly listed in literature as "repeat-flowering" roses. At the Minnesota Landscape Arboretum, they bloom heavily in spring, stop flowering in summer, and produce a few blooms again in fall. At the other extreme are cultivars like 'Chuckles', 'Nearly Wild', and 'Ballerina', which bloom heavily throughout spring, summer, and fall. From a flowering standpoint, these three cultivars are much more valuable as landscape plants.

'Jens Munk', one of the Explorer Series roses developed by Agriculture Canada at Ottawa, Ontario, is a large, hardy rose with minimal dieback. Its R. rugosa background gives it a wonderful combination of hardiness, disease tolerance, rebloom and fragrance.	The Floribunda 'Nearly Wild' produces medium pink, moderately fragrant, 2-inch, single flowers. It experiences significant winter dieback, but can regrow vigorously and bloom profusely throughout the growing season.

The rebloom patterns for repeat-flowering cultivars and species are described in Table 3. The bloom season is divided into three periods (June, July, and August/September). Each cultivar's floral density is recorded as none, slight, moderate, or heavy for each of the three periods of the bloom season.

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