Plant Trials in Iowa

Due to a lack of regionally specific research, demonstration, and outreach surrounding newly introduced ornamental plants for Central Iowa, the Iowa Arboretum & Gardens established an ornamental trial garden for the categories of herbaceous perennials and shrubs in the Spring of 2023. This public-facing trial garden provides beauty, education, and outreach to the people of Iowa in a form viewable to the public, allowing for year-round visibility and observation of these plants.

The purpose of this garden is to evaluate the long-term performance of perennial and shrub varieties and report the findings to the introducing entity, the horticulture industry, and the public to help give insight and make educated recommendations for plant varieties to be grown in Iowa. Most people outside of the Midwest would characterize the climate and weather in Iowa as “the dream” in Zone 5. However, the growing conditions can include extreme winds, periods of heavy rainfall, and intense thunderstorms. Winter brings bitter blizzards, weeks with temperatures below zero degrees Fahrenheit, and months of snow sitting on crowns of plants. Recently, extreme conditions hit Central Iowa, particularly drought, months without rainfall, and a devastating derecho that left many without trees.

Plants are evaluated for vigor, uniformity, resilience, and tolerance to environmental and biotic stresses. Data and photographs are collected once a month during the growing season (April – October) by staff as well as by members of the Trial Garden Committee. The data is then reviewed alongside photographs by the committee and arboretum staff to designate varieties as Iowa Arboretum Top Performers. The public also has a chance to have their voice heard by selecting and commenting on their favorite plants when they visit the garden.

Plants are evaluated on a weekly basis using these factors to help measure their success:
● Vigor (Compared to plants in the same genus/species, no lodging)
● Uniformity (Across plants in a variety)
● Disease/pest resistance (Comments about pest and disease pressure, rabbit resistance, susceptibility to disease compared to claims)
● Floriferousness (Qualitative rating of flower coverage)
● Proliferation (Seediness, weediness, potential to become invasive)
● Resilience (Ability to withstand drought, flood, unpredictable weather events)
● Seasonal Interest (Gives weight to unusual flowering period, fall color, and winter interest)
● Survival (Ability to survive growing conditions, lifespan evaluation)

Evaluation will be conducted for the life of the plant, giving us realistic understanding of the lifespan and true hardiness of varieties. However, plants will be selected as Top Performers after three years for perennials and five years for shrubs.

In the area of research, this ornamental trial serves to compile and evaluate plant performance in the climate of Central Iowa. The data collected on these plants serves several purposes.

The first is to provide the plant breeder or company introducing the plant information about the plant’s performance in this region. That information can then be used to influence and drive future breeding and selection efforts.

Second, this data can be used by local nurseries and retail operations to make informed decisions about plants to offer to the public. A regional trial garden gives the local industry the chance to see how these plants perform in the area before they choose to sell them.

Third, this data can inform the public about plants they should be selecting for perennial landscapes in Iowa. The operation of a trial garden like this directly promotes the responsible introduction, cultivation and distribution of new plants that have ornamental horticultural value. This program is used to recommend plant selections for gardeners to be more successful in their own gardens. Plants that perform successfully in the trial are shared during speaking engagements by staff, during plant walks and short courses, and through press releases to trade publications, our newsletter, and recommendations to Iowa State Extension. The trial garden as a whole is used to teach plant identification to guests, volunteers, and local horticulture students. The trial also serves as a library for guests to observe seasonal interest, from foliage color emerging in spring to bloom time and color, fall color, and even winter interest.

Fourth, gardeners can also observe how trial plants are managed to be better informed on species-specific garden best practices. A trial garden also helps influence plant offerings at nurseries and retail garden centers by taking the guesswork out of what plants will survive in the Central Iowa climate. By inviting our industry to participate in the trial process, they can see the long-term survival and success of the new plants being offered by suppliers and make ordering decisions based on a variety’s performance. Likewise, providing a consumer evaluation day gives insight into what plants consumers in this state want.

Finally, this garden is used in educational programming, teaching the public about topics ranging from garden management, plant identification, weed management, pruning, and designing for multiple seasons of interest. Staff use the data, photographs, and physical garden as a tool to teach these topics as an informal outdoor classroom. As the plants are managed, staff explain and demonstrate best practices while using the garden as a library of plants to use in the Central Iowan landscape.