Evaluating perennials in the Rocky Mountains

The purpose of the trial garden at Colorado State University in Fort Collins is to evaluate new perennial plant species and cultivars under the unique Rocky Mountain environmental conditions. Plants are evaluated for vigor, uniformity, floriferousness and tolerance of environmental and biotic stresses. The Perennial Trial program at CSU is designed to test newer perennial cultivars that have been introduced in the past three years or less. Entries in this trial are grown for three summers and two winters before they are switched out for new entries.

About the Trial Garden

CSU’s Flower Trial Garden, which draws thousands of visitors each year, relies on student gardeners, volunteers and industry supporters and experts who help provide detailed analysis of plant performance. Colorado State Extension Master Gardeners play an essential role in planting and maintenance of the garden. The outcome of this research is valuable to the industry and home gardeners alike. That’s because the Rocky Mountain region has unique growing conditions, characterized by high altitude, intense solar radiation, drying winds, severe hailstorms, large fluctuations between day and night temperatures, as well as a season-long need for irrigation.

The Perennial Trial Garden receives no direct public funding. It is funded primarily by fees from plant breeding companies that submit entries to the trials. The garden also receives donations from industry associations, foundations, nurseries, plant producers and other companies in the green industry.

Selection of “Top Performers”

On November 20, 2017, a conference call was convened with CSU staff and the Perennial Trial Garden Subcommittee. Pictures of entries from the 2015 planting were posted to the Perennial Trial website for review. Data from the growing season were compiled and emailed to each evaluator prior to the conference call for review. After discussion and looking at the pictures taken throughout the season, each plant was voted on by each member of the committee as to whether it should be awarded the designation as a “Top Performer.”

Performance Evaluation

Photos and data on plants and flowers were collected on a biweekly basis from May to early October. Dead plants in the trial were not considered in the biweekly evaluation; thus, the ratings given only reflect the live plants. Members from the Perennial Trial subcommittee also wrote comments for each plant in June, July, August and September. Plants and flowers were rated 0 to 5 using the following scale:

  • 0 = Dead/No flowers
  • 1 = Poor: Plants are very sick or dying, extremely few flowers
  • 2 = Below Average: Plants are unattractive in some form, for example, leggy growth habit, chlorotic or low vigor, flowers are few and occurring sporadically
  • 3 = Average: Plant appearance with growth characteristics that would be expected for the time of season; flowers would be few but uniform across the plants
  • 4 = Good: Plants look attractive (foliage, growth habit); flowers are blooming strong and showy
  • 5 = Excellent: Plants are very healthy and uniform; flowering is impressive

“Top Performer”

Perennials from the 2017 CSU Perennial Trial

(Dianthus ‘Kahori’)

Noted as a real step up in breeding, evaluators described this as the new standard for Dianthus. The vibrant pink flowers covered the plants at peak bloom and created a mat of stunning color against the green foliage. This entry was superior for an extremely long period of bloom and exceptional uniformity. It has proved to be reliably hardy and would look great in a rock garden, ground beds and borders, and is a great choice to use in containers since it was always in bloom.

This selection remained compact and has great heat tolerance during the peak of summer temperatures. It was very attractive even during its first year in the garden and has only gotten better each year since it was planted.

Bred by Bartels.

(Lavandula × intermedia ‘Niko’ PP24193)

The abundant, tall, graceful flower stalks are held high above the foliage for maximum display. Besides being uniform, all plants had excellent cold hardiness. They do best when grown on the drier side to avoid lodging of the flower stalks. Pollinators were very attracted to this plant, and it has a high oil content that makes it attractive for commercial production.

Bred by Cultivaris.

(Helleborus Interspecific ‘JWLS’)

This winner was selected in part for its unique ability to bloom from early spring till late summer. It added a touch of elegance to the garden with a classic white flower, attractive glossy foliage and a very attractive dense, compact growth habit. Not only did the nodding flowers change color over the season, but the foliage can be evergreen in a protected area for year-round interest. Besides making a great groundcover, the flowers are useful for cut-flower production.

Bred by Hilverdakooij.

(Phlox paniculata Flame® Blue)

Abundant blue flowers that fade to white were held upright on sturdy stems with dark, emerald-green leaves that never lodged despite overhead irrigation used in the garden. Flower color was a subtle blue that is strongest in early summer and again late in the season as the temperature cools. It was a relatively early bloomer starting in mid- July. Self-branching plants had a full and uniform growth habit. Plants had superior resistance to powdery mildew.

Bred by Bartels.

(Veronica Ronica™ Dark Pink)

Big, fat and stout flower spikes put on an eye-catching show of dark pink flowers. Plants kept a formal appearance with great uniformity with dark, emerald-green foliage that really sets off the pink flowers. Bloom period was very long especially if deadheaded. The plant had superior resistance to powdery mildew compared to other entries growing in the trial. Growth habit was very full and dense.

Bred by Danziger.

Class of 2016, “Too Good to Wait” Award

The Perennial Trial Garden Subcommittee likes to award the “Top Performer” designation to superior plants that have been in the ground two winters and three growing seasons. This category is to acknowledge an upcoming plant that has been in the ground one winter and two growing seasons and shows excellent performance thus far in the trial. The following plant impressed the Perennial Trial Garden Subcommittee so much that they designated the category name: “Too Good to Wait Performer.”

(Echinacea ‘TNECHKIO’ PPAF)

The sheer mass of vibrant flowers drew people from across the garden. Prolific flowers formed a solid canopy of blooms over the plants, a characteristic that is sure to spell success for the gardener. The intense orange color almost seemed to glow at its peak. Flower color faded to an attractive shade of pale yellow to maintain a long season of bloom. Foliage was a unique shape and attractive early in the season. Plants had a uniform growth habit and good branching. The KISMET™ series also features colors of raspberry, red and yellow.