May 16, 2007 | By: Laura Skillman
PRINCETON, Ky.

For many Kentucky gardeners roses are a must for their summer landscape, but some gardeners shy away from them because they fear roses are too high maintenance. However, today there are roses that require much less maintenance to produce glorious blooms.

Kentucky growers wanting to maintain the good health of their rose cultivars are almost obligated to use repeated applications of fungicides throughout the growing season to prevent black spot, the main disease that plagues the plants. Caused by the fungus diplocarpon rosae, it is a serious problem every year in Kentucky’s warm, humid growing conditions, causing leaves to become spotted, turn yellow and drop from the plant. If rose growers could grow genetically resistant or disease tolerant roses, they would benefit from improved performance and reduced fungicide use.

Fortunately, many of the new shrub roses such as the Knockout series show resistance to black spot and other diseases. These new shrub roses are gaining in popularity with many gardeners.

“Knockout roses have changed things. They have helped revitalize rose growing,” said Tim Phillips, a University of Kentucky tall fescue breeder by trade, but a rose expert in his spare time. Phillips donated, planted and maintains the rose garden at The Arboretum in Lexington. 

The Knockout roses are nearly carefree. While they won’t provide the large, long-stemmed flowers fancied by florists nor are they as fragrant, they do make for showy shrubs throughout the summer and into fall, he said.

Phillips warned that though disease resistance makes maintenance easier, Japanese beetles are still a problem for any rose, so protecting the plant from these pests is still important.

With the success of these roses, many other companies are working to develop more carefree roses. Also, Phillips noted, many old varieties that were grown by our ancestors possess some of these desirable traits.

“There are rose varieties that can be planted and grown as easily as azaleas and boxwoods, and are easier than many shrubs,” he said. “You can prune if you want to make them tidy and dead head them, but you don’t have to.”

But for growers looking for disease resistance, it is best not to believe everything you hear or read, cautions John Hartman, UK plant pathologist. Showy descriptions of rose cultivars with their disease resistance claims can be found in many plant and nursery catalogs. Unfortunately, assertions of disease resistance and a lack of a need for spraying can be anecdotal and without proper experimental controls, he said. He advised growers to be skeptical of these types of claims, at least until they see the results of science-based research.
Kentucky gardeners can find scientifically proven facts on many of these roses through the Cooperative Extension Service. Plant pathologists at the University of Tennessee are testing these "no-spray" roses at various locations, one of which will be in the Cumberland Plateau which has a climate similar to that of northern Kentucky, Hartman said.

From their rose plots they already have some preliminary results that should be of interest to Kentucky rose growers. Out of this test of 64 roses, they have identified 10 shrub rose cultivars that could claim the title of "no-spray roses.” In 2007, these cultivars will be tested again to confirm their resistance. UT will add to the test more cultivars, all with resistance claims in industry publications or catalogs. 

“This is a good example of land-grant university research that benefits gardeners throughout the region and how the Cooperative Extension Service collaborates to foster rapid dissemination of science-based results,” Hartman said. “At the same time that Tennessee gardeners might benefit from UK work on shade tree bacterial leaf scorch or pine tip blight diseases, for example, Kentucky gardeners can benefit from UT work on disease-resistant roses.”

Roses in the UT research found to be resistant were yellow roses Carefree Sunshine and Topaz Jewel; red roses Homerun and Knockout; pink roses Hansa, Pink Knockout, Wildberry Breeze, and Pretty Lady, which is a light pink; and white roses Snowcone and Wildspice. The shrub rose cultivars Belinda's Dream, Crystal Fairy, Fairy Queen, Lovely Fairy, and Wild Thing were moderately resistant, but not in the "no-spray" category. 

Kentucky is a good place to grow vast varieties of roses and, while some may take more care than others, they are worth the effort, Phillips said. “Nothing else will give you blooms five months out of the year.”

As breeders work to improve varieties, the weekend gardener will see more and more low-maintenance varieties become available. “A lot of people have fond memories of a grandmother’s rose garden and are willing to give Knockout a try,” Phillips said.

Some varieties Phillips classifies as low maintenance, in addition to the Knockout shrub roses, are rugosa or hybrid rugosa, old garden roses, Dr. Buck Griffith’s varieties, and several from the list of disease resistant varieties from evaluation trials at Longwood Gardens in Pennsylvania. Examples of these can be seen at The Arboretum.

Contact: 

Tim Phillips, 859-257-5020, ext. 80769, John Hartman, 859-257-7445, ext.80720