FAYETTEVILLE, Ark — Some plants can’t be left out in the cold, but an ongoing experiment by University of Arkansas researchers examines underused deciduous and evergreen shrubs and trees to see which ones can.. Plants that prove themselves offer landscaping alternatives in three USDA cold hardiness zones found at various locations throughout the United States.

In 2004, Jon T. Lindstrom, associate professor of horticulture, and Jim Robbins, extension specialist with the University of Arkansas Division of Agriculture, evaluated the first “graduating class” of plants that they placed in the ground in 1999. The researchers developed plant testing sites in Fayetteville, Little Rock and Hope, which represent three different cold-hardiness zones within the state and across the nation.

The program has several goals, including evaluating ornamental plants that can be used as screens or hedges in a garden landscape, evaluating the cold hardiness of broadleaf evergreens, and evaluating plants rarely seen in Arkansas nurseries or landscapes. These plants may be new to the commercial market, or may be common in other states with similar cold-hardiness zones but not common here, Robbins said.

The researchers get the plants from commercial nurseries that want to “test drive” new plants, or they propagate the plants themselves. They have received plants from nurseries all over the country and Canada, including Michigan, Iowa, Oregon, Washington, Georgia, South Carolina, New Jersey, Oklahoma, Louisiana, British Columbia and Texas.

They have tested plants from azaleas to viburnums, with lots of holly, crape myrtles and oaks thrown in for good measure. Every year since 1999, they have planted an average of 15 new plant varieties at the three sites.

“We’re generating information that should be of interest to the nursery industry,” said Robbins. Landscapers and nursery companies constantly seek different plants to offer variety to gardeners, but often lack data to know whether novel plant types will live and die in a given hardiness zone.

The plant evaluation program can assist nurseries because it evaluates several plants of the same variety at multiple sites over multiple years. It’s one of the most comprehensive evaluation programs at a university, Robbins said. The quantitative data will give nurseries vital information they need to make decisions about which plant varieties to stock and sell.

“You never know what the weather is going to be like, over time, in just one year,” Lindstrom said. In a given year, “you may get that test summer or test winter, or a drought, and then you can see if the plants will make it through.”

As the program has continued through the years, some of the plants proved intolerant to the colder climate in Fayetteville, making them undesirable for growing in this part of the state. Some of the plants, like the Loropetalum chinense, or Chinese fringe flower, stayed alive in Fayetteville, but did not flower in the spring. Others, like the dwarf crape myrtles, died back in Fayetteville and did not attain their expected height.

However, the researchers did find plants that grew well in all the zones, like the Dixie DreamT holly. Another plant that grew well at all three sites, Itea virginica, also known as Henry’s garnet, sported flowers in May and rich maroon-colored leaves in November and easily propagates through cuttings.

Some plants did not live up to the expectations of the researchers.

“There were plants we didn’t like regardless of site,” said Lindstrom, recalling one plant that had variegated leaves that returned with new growth that had solid-colored leaves. Another plant had no improvements to recommend it over already existing, easy-to-find varieties.

The researchers have devised an evaluation scale to help nurseries make decisions about which of these underused plants might appeal to customers in the different cold hardiness zones.

The plant evaluation program continues to grow, and plants will be evaluated as the shrubs and trees planted in 2000 through 2004 reach their fifth year. The researchers continue to look for little-known, unusual plants to test. This year, they plan to plant a reportedly frost-tolerant eucalyptus tree.

They have begun to disseminate the information they have accumulated since 1999 through reports that are available on the Web. For information on the plant evaluation program, please see http://www.uark.edu/campus-resources/cotinus/arboretum_html/planteval.html