Roses are classic garden plants with vast emotional appeal. They’re familiar, nostalgic and symbolic. In recent decades they’ve shed their reputation of being fussy and prone to disease, thanks to groundbreaking cultivars like Knock Out (‘RADraz’), which turned 20 in the year 2020. The breeding of disease-resistant roses has given them entry to spray-free pollinator-friendly gardens, while a widened range of sizes and habits—along with our changing tastes—has moved them out of the formal dedicated rose garden and into diversely planted spaces of all styles and purposes. In short, roses have re-staked their claim as a staple in American gardens.
That said, a gardener looking to add a rose to her garden faces dizzying choices and, often, a lingering wariness that the plant will require chemical sprays. There are tens of thousands of rose cultivars circulating today, with new introductions entering the market each year. How to choose one? The non-profit American Rose Trials for Sustainability (ARTS) is working to simplify this decision by identifying the best cultivars for different regions.
How ARTS Got Started
Founded in 2012, ARTS is a collaboration between scientists, university educators and rosarians who partner with public gardens and rose-breeding nurseries. The program was inspired by Earth-Kind, a trialing program run by Texas AgriLife Extension Service, and All-America Rose Selections, a breeder-run trial that wound to an end in 2013.
Dr. David Zlesak, a professor of horticulture at the University of Wisconsin–River Falls, is one of the founders of ARTS. First he modeled a program after Earth-Kind for northern states. Cultivars were studied for four years in the ground, plus additional testing, and finding space to run the program became an issue, especially as interest from breeders ramped up. Then the closing of All-America Rose Selections (AARS) created an opportunity to build a new trialing system with a national scope.
While the economic downturn that began in 2008 played a big part in AARS’s ending, David notes that the program had also been late to add low chemical input to its criteria for winning roses, though this had become steadily more important to consumers. He recalls conceptualizing the new rose-trialing program:
“We wanted it to be strong and meet needs from the beginning, so we had conversations with stakeholders—growers, landscapers, homeowners—to ask, what do you value most in a rose?” He says the answer among all groups was very consistent. Nurseries, plant professionals and gardeners all wanted a “truly healthy rose that provided ornamental appeal throughout the growing season and was not chemically dependent.”
The fledgling ARTS group now had a definition for “best roses,” but they also wanted to judge them from regional perspectives. The team recognized that winter hardiness is just part of the story. They decided to define regions using the Koppen climate classification system instead of the USDA Plant Hardiness Zones. Preferred by ecologists, Koppen classification breaks the United States into nine regions based on air temperature, precipitation and humidity.
“Really the biggest challenge was pitching the regionality aspect of the program,” David says, “because the climate system we use was not too familiar” among the nurseries that might enter roses for testing. However, the breeders came to recognize the more precise regions as an asset.
How the Rose Trials Work
With criteria defined and the regions mapped out, ARTS designed science-based testing to take place at partner sites across the country—ideally, two sites in each of the nine regions. These sites include botanical gardens, college and university campuses and public spaces. Staff or volunteers at each site are trained to manage the roses and regularly, precisely score them on health and quality of foliage; presentation and quality of flowers; and overall growth habit.
The cultivars ARTS tests are entered by the nurseries that have bred them, with a nominal entry fee that covers necessities like costs associated with the ARTS website. The organization is a 501(c)(3) foundation, meaning it’s non-profit, and David notes they’ve carefully set up systems of checks and balances to manage potential conflicts of interest.
Cohorts of rose cultivars are tested for two years, with each cohort also including two “control roses”—prior winners that have proven themselves in multiple regions. The roses are arranged in three planting blocks spaced at least four feet apart. Each block contains a sample of every cultivar, but they are arranged in different ways. David explains that the spacing of the beds and the randomized layout “reduces the variables and provides better representation data on each plant.”
Because the trial runs for just two growing seasons, the roses are provided with supplemental water as needed—just enough to meet the inch per week afforded even drought-tolerant plants as they’re getting established. No pesticides or fertilizers are applied, however, and pruning is limited to the removal of dead wood over the winter.
The winners of the first trial, planted in 2014, were announced in 2017. To date, ARTS has designated 44 Local Artists, which have been judged outstanding performers in at least 1 Koppen climate region, and 12 Master Roses, which are cultivars that have been named Local Artists in at least 4 Koppen climate regions. Local Artists have been identified for six of the nine climate regions, but testing is ongoing in all but the Aw (tropical wet/dry season) climate—the southern tip of Florida—where the team is still seeking a partner site. The ARTS website arranges the Local Artists by region to make it easy for gardeners to choose. Of course, David notes, individual results can vary, but when you choose a Local Artist from your region “there’s a high likelihood you’ll be successful.”
Explore the ARTS website to learn more: http://www.americanrosetrialsforsustainability.org.