Perennial trials at the W.D. Holley Plant Environmental Research Center (PERC) on the Colorado State University campus reveal a slate of 2013 Top 10 performers in challenging Rocky Mountain conditions.

Photos courtesy of Vanessa Sandoval

Sparkling blue skies and snow-capped peaks compose the postcard image of Colorado, and it’s an image that’s well deserved. With ample sunshine and glorious scenery, the Centennial State is a vacationer’s delight.

If you’re a plant, however, the environment can present quite a few challenges. So about four decades ago, Colorado State University established the W.D. Holley Plant Environmental Research Center on the school’s Fort Collins campus, with trial gardens prepared to evaluate annual selections. The perennial trials were created in 2007 in response to increased interest in new perennial cultivars.

The purpose of the trial garden is to evaluate perennial plant species and cultivars under our unique Rocky Mountain environmental conditions. Fort Collins is located on Colorado’s Front Range, in hardiness zone 5. Our growing conditions are characterized by high altitude, intense solar radiation, drying winds, severe hailstorms, large fluctuations between day and night temperatures and a season-long need for irrigation. Plants are evaluated for plant vigor, uniformity, floriferousness and tolerance to environmental and biotic stresses.

For the class of 2013, selections were planted in 2011, requiring that they perform through two winters and three growing seasons. Data (ratings and photos) were collected every two weeks (May to early October). Plants were evaluated once a month by members of the Perennial Trial subcommittee. The Perennial Trial subcommittee met in October to review data and photos to vote on which entries should be designated a “Top Performer.”

Preparing the plants

The plants tested at the PERC trial gardens are submitted by a number of breeders and growers from around the country (see sidebar), many of which have participated in the trials season after season.

Vegetatively propagated plants submitted by our contributors did not arrive all at the same time or at the same growth stage. Most of the new entries were planted in the garden in June of 2011 for evaluation in fall of 2013.

Some vegetative varieties were received as plugs and transplanted into 4-inch pots shortly after arriving at CSU. They were planted into the garden when they established well in a 4-inch pot. Some entries arrived in larger containers and were planted directly into the garden.

Greenhouse prep included application of fertilizer for each day the plants were watered – with the exception of being irrigated every weekend with clear water. Banrot and Rootshield were applied to all plugs immediately upon arrival and prior to potting; miticide and insecticidal soap also were employed to discourage mites and aphids.

Planting beds were cleaned and amended with compost, and entries were sited in beds that corresponded with their preferred sun or shade requirements. Spacing was based on the estimated mature size of each plant, as well as how many specimens were received. An irrigation audit was conducted at the beginning of the season to determine the appropriate rate and beds were watered with 1 to 1.5 inches of water per week, depending on the variable precipitation and the need to establish newly planted varieties. During the winter, plants were watered by hose and sprinkler as needed during extreme dry spells.

After planting, Osmocote was applied to all beds; Greencare water soluble fertilizer also was used. Flowers were deadheaded as needed, and after the first killing frost in the fall, plants were cut back to the ground—unless they have winter interest. Weeding was performed by hand, and disease and pest controls were applied as needed.

Ready for evaluation

Photos and data on plants and flowers were collected on a biweekly basis from May to early October. Members from the Perennial Trial subcommittee also came and wrote comments for each plant in June, July, August and September. Plants and flowers were rated 1 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, etc.); flowers are blooming strong and showy

5 = Excellent: Plants are very healthy and uniform; flowering is impressive

Height and width measurements were taken once toward the end of the growing season; this was done to get a feel for the average size of the mature plants and each variety’s growth performance.

On October 23, 2013, a conference call was convened with CSU staff and the Perennial Trial Garden subcommittee. Pictures of entries from the 2011 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 committee member voted on each plant to determine whether it should be awarded the designation as a “Top Performer.”

For the class of 2013, five selections were named “Top Performers”; four were acknowledged “New Top Performers”; and one plant proved to be so promising that the judges created a new category: “Too Good to Wait Performer” (see sidebar below).

Top performers for the 2013 season

Anemone hupehensis ‘Pretty Lady Diana’

Anemone hupehensis ‘Pretty Lady Diana’ (Pretty Lady Diana windflower; PP22,332) from Blooms of Bressingham produced lots of deep pink blooms in August until early October; the plants remained healthy and vigorous all season long. Pretty Lady Diana has a compact habit, reaching about 25 inches tall by 23 inches wide. Judges mentioned that the plants would not take up a lot of space and would be great for a small garden or in a mixed border. The plant was bred by Yoshihiro Kanazawa.

Survival rate in PERC trials was 100 percent.

Baptisia Decadence® ‘Lemon Meringue’

Baptisia Decadence® ‘Lemon Meringue’ (Lemon Meringue false indigo; PPAF) from Walters Gardens and Proven Winners continued to amaze judges in the 2013 growing season. Vigorous, strong plants support clear, crisp yellow flowers that turn a lighter pastel with age. Although the bloom time was brief, the plants had an open and airy habit and nice foliage to enjoy the rest of the season. Lemon Meringue grew to about 41 inches tall by 37 inches wide, encouraging one judge’s comment: “Huge plants.” Another described the plant as being of “premium quality.”

Survival rate in the PERC trials was 94 percent.

Agastache ‘Blue Boa’


Geranium ‘Eureka Blue’

Geranium ‘Eureka Blue’ (Eureka Blue cranesbill; PP22,270) from Blooms of Bressingham continued to impress judges with the extreme color impact of its bright violet blooms. Flowering began at the end of May and continued to the end of July. Judges mentioned that this plant would make a great landscape variety, because it looks good even when not in bloom; plants had healthy foliage all season long. Vigorous with a uniform habit, Eureka Blue reached 26 inches tall by 38 inches wide. The plant was bred by Brian Kabbes.

Survival rate in the PERC trials was 100 percent.

Hibiscus Summerific® ‘Cranberry Crush’

Hibiscus Summerific® ‘Cranberry Crush’ (Cranberry Crush rose mallow; PP21,984) from Walters Gardens and Proven Winners continued to be a fantastic grower with its dark red blooms and dark, glossy foliage. The leaves were deeply lobed and had an attractive dark red hue that matured into dark green. Judges noted that these plants gave the garden a dramatic tropical effect and would be great for late summer color in the back of a border. Upright, uniform growth to 60 inches tall by 44 inches wide. The plant was bred by Clarence H. Falstad.

Survival rate in the PERC trials was 100 percent.

Nepeta ‘Novanepjun’ Junior Walker™

Nepeta ‘Novanepjun’ (Junior Walker™ Catmint; PP23,074) from Star Roses and Plants/The Conard-Pyle Co. sports blooms that are bright lavender beginning at the end of May and continuing strong until mid-August. Described as vigorous and floriferous, plants grew to an intermediate size of 18 inches tall by 28 inches wide and filled in the space quickly, making a great groundcover. The plant was bred by Michael S. Dobres.

Survival rate in the PERC trials was 100 percent. New top performers for the 2013 season

Anemone hupehensis ‘Pretty Lady Emily’

Anemone hupehensis ‘Pretty Lady Emily’ (Pretty Lady Emily windflower; PP22,303) from Blooms of Bressingham had great flower power late in the season; judges stated that the double, light pink flowers were unique, and that the plant was an “amazing flowering machine.” Healthy growth started out non-uniform, but by the end of the season filled in nicely with a more uniform habit of 22 inches tall by 20 inches wide. The plant was bred by Yoshihiro Kanazawa.

Survival rate in the PERC trials was 94 percent.

Penstemon schmidel ‘Blue Riding Hood’

Penstemon schmidel ‘Blue Riding Hood’ (Riding Hood blue beardtongue; PP23,066) from Pacific Plug and Liner were described by judges as strong with a good blue flower color (true blue with a purple throat), putting on a great flower show in June. It was noted that the plant produced seedheads that should be deadheaded. Growth habit was uniform and compact, reaching 18 inches tall by 21 inches wide, with glossy, medium-green foliage. The plant was bred by Remy Lubbe.

Survival rate in the PERC trials was 89 percent.

Phlox glaberrima ssp. triflora ‘Triple Play’

Phlox glaberrima ssp. triflora ‘Triple Play’ (Triple Play smooth phlox; PP21,329) from Creek Hill Nursery and Eason Horticultural Resources was described by judges as serving several functions. The plant’s semi-double pink blooms complemented variegated green and white foliage, which provided an extended season of interest after the flowers faded. With a compact, uniform habit, Triple Play reached 20 inches tall by 21 inches wide. The plant was bred by Janet Sacks and Martin Schafer.

Survival rate in the PERC trials was 100 percent.

Salvia nemorosa ‘Balyriclu’ Lyrical Blues

Salvia nemorosa ‘Balyriclu’ (Lyrical Blues meadow sage; PP22,919) from Darwin Perennials had great flower power with bright purple blooms; after deadheading, the plants produced a nice secondary bloom. Flowers remain attractive as they age, and flower stems keep their color for a long time. Clean foliage and a compact, uniform habit—reaching 24 inches tall by 20 inches wide—made the plant enjoyable even when not in bloom. The plant was bred by Lynne Knosher.

Survival rate in the PERC trials was 100 percent.

For more information on the PERC plant trials, visit

Dr. James E. Klett is professor in the Horticulture and Landscape Architecture department at Colorado State University, Fort Collins, where he also serves as director of the W.D. Holley Plant Environmental Research Center (PERC) and faculty coordinator for PERC’s Annual and Perennial Flower Trial Gardens. He can be reached at David Staats is a research associate in CSU’s Horticulture and Landscape Architecture Department, specializing in ornamental plants; he can be reached at Vanessa Sandoval is a graduate research assistant and perennial trial coordinator at CSU; she can be reached at

“Too Good to Wait”

Patience is a virtue, but sometimes it’s just too hard to contain yourself. The Perennial Trials Committee at Colorado State University found itself in just such a situation when it evaluated one particular plant that, according to the guidelines, wasn’t technically ready. This up-and-comer plant had been in the ground one winter and two growing seasons – short of the standard two winters and three growing seasons – but it showed such promise that the committee created the category name, “Too Good to Wait Performer.”

Blue Boa hummingbird mint (Agastache ‘Blue Boa’ PPAF) from Terra Nova Nurseries impressed judges with its nonstop flower power. Plants produced bright lavender blooms heavily throughout the growing season. Judges stated that this plant is drought-tolerant, a bee attractor and will “bring great to joy to home gardeners.”

Ninety percent of the plants survived in the trials – a good showing for a relatively new plant – and they rose to 53 inches tall by 46 inches wide. Some of the evaluators’ comments included: “very vigorous; uniform habit; good color impact; full color; a giant; huge and colorful.”

Thanks for the support

The Department of Horticulture and Landscape Architecture at Colorado State University would like to thank the many plant and seed companies that continue to participate in the trials year after year. Without their cooperation and support, the research done at the trial garden would not be possible. This year, the following 13 plant and seed companies participated in the trials, entering 141 varieties of herbaceous perennial plants:

  • Ball Ingenuity
  • Blooms of Bressingham
  • Darwin Perennials
  • Creek Hill Nursery & Eason Horticultural Resources
  • Greenfuse
  • Kieft Pro-Seed
  • Pacific Plug and Liner
  • Selecta
  • Skagit Gardens
  • Star Roses and Plants/Conard-Pyle Co.
  • Suntory
  • Terra Nova Nurseries
  • Walters Gardens/Proven Winners