Perennial Trials reveal top 8 performers in Rocky Mountain conditions

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After three seasons growing in the challenging conditions of the Rocky Mountains, eight perennial plants have been named “Top Performers” by researchers at Colorado State University.

Evaluating perennials in the Rocky Mountains

The purpose of the trial garden is to evaluate new perennial plant species and cul­tivars under the unique Rocky Mountain environmental conditions.  Plants are evaluated for plant vigor, uniformity, floriferousness and tolerance to environmental and biot­ic stresses.  The Perennial Trial program at Colorado State University 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 and 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.

Performance Evaluation

Photos and data on plants and flowers were collected on a bi-weekly basis from May to early October. Dead plants in the trial were not considered in the bi-weekly evaluation; thus, the ratings given only reflect the live plants. 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 0-5 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, i.e. – 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

Selection of “Top Performers”

On November 16, 2016, a conference call was convened with CSU staff and the Perennial Trial Garden Subcommittee. Pictures of entries from the 2014 planting were posted to the Perennial Trial website for review. Data from the growing season was 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”.

“Top Performer” Perennials from the  2016 CSU Perennial Trial

 WINDWALKER® Big Bluestem from Plant Select®

(Andropogon gerardii  ‘P003S’)

This is an ornamental grass with great multi-season interest with beautiful soft blue foliage that changes to a dark maroon lavender that persists even into the winter.  The plant adds impressive height to the border with a narrow growth habit that reaches about 6’ tall.  This is a great choice for a xeriscape area, as it can thrive with little or no supplemental irrigation.  Avoid overhead watering and over-fertilization to maintain compact plants and prevent lodging.

Alexander’s Great Brunnera from Terra Nova Nurseries, Inc.

(Brunnera macrophylla ‘Alexanders Great’ PP25,789)

This is a unique Brunnera of “monster” growth proportions which is an excellent choice to add structure to the garden.  The large size also helps show off the heavily silvered leaves resulting in a dramatic statement for the garden.  It makes a great foliage plant for shady areas but also has a good display of blue flowers that creates a light, airy appearance.  It can be used as a very attractive groundcover that is about knee high, but also makes a striking specimen.  This is one of the few perennials that was selected for the “Too Good to Wait” award in 2015 and did not disappoint during the 2016 season. Make sure to give this plant ample space to show off its naturally uniform mounding habit and beautiful flowers.

 Carnival Rose Granita Heuchera from Darwin Perennials

(Heuchera x hybrid ‘Carnival Rose Granita’PPAF)

One of the best in the Carnival series, Rose Granita is unique among Heuchera in that the foliage reflects light and even seems to glow at times.  Its foliage has a composite of pink, purple and green, combined with a silver overlay that seems to change with the angle of the sun as well as the season for a truly mesmerizing appearance.  Beautiful from a distance, this plant only gets more impressive up close as the leaf variation starts to come into focus.  Use in mass plantings or as a small specimen in the shade.  The plants have a very uniform growth habit and a light pink flower that complements the foliage nicely.

 Forever Purple Coral Bells from Terra Nova Nurseries, Inc.

(Heuchera ‘Forever Purple’PPAF)

Aptly named, Forever Purple’s leaves are a deep, rich purple color that is maintained all season without fading.  The best and most vibrant purple leaved Heuchera currently on the market sports glossy foliage that seems to make the color “bounce” off the leaf.  It is grown mostly for attractive foliage which also has fluted edges.   Plants have good vigor and a very uniform growth habit.  It would make a great choice for shady areas or combos.

Summerific® Cherry Cheesecake Rose Mallow from Walters Garden/Proven Winners

(Hibiscus x ‘Summerific® Cherry Cheesecake’)

Saucer sized flowers are a stunning contrast of rich cherry-red and bright white which gives a very tropical or exotic feel to the landscape.  This selection is rated highly for its ability to produce huge flowers evenly over the entire plant.   Plants are very uniform and healthy with foliage that reaches all the way to the ground.   Be patient with this hibiscus as it comes up very late in the spring, but is well worth the wait when the showy flowers start to open in late July.

 CrazyBlue Russian Sage from Darwin Perennials

(Perovskia atriplicifolia ‘CrazyBlue’USPP25639)

Besides the prolific blue flowers, this entry is noted for a very attractive growth habit that is smaller than the species and is not susceptible to lodging even with overhead irrigation.  Growth habit improves with age and with time makes a very attractive compact mound of silver gray foliage.  Plants appear dense with good branching and have a very long bloom period.  This selection thrives in a dry location and maintains a slightly more compact habit.

 Glamour Girl Garden Phlox from Walters Garden/Proven Winners

(Phlox paniculata ‘Glamour Girl’)

This variety is described as “One of the best garden phlox introduced in a very long time”.  The period of bloom is impressively long and provides the garden with abundant vibrant salmon colored flowers.  Flower color did not fade and the plants create a very upright and uniform overall appearance with no lodging.  This selection seems to be fairly mildew resistant when compared to other garden phlox in the trials.

 Class of 2015 – “Too Good to Wait” Award

The Perennial Trial Garden Sub-committee likes to award the ‘Top Performer’ designation to superior plants that have been in the ground 2 winters and 3 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 Sub-committee so much that they designated the category name: “Too Good to Wait Performer”.

Kahori® Border Pink from Bartels

(Dianthus ‘Kahori’)

Prolific blooms cover the plants at peak bloom and creates a mat of vibrant pink flowers.  This entry is superior for a long period of bloom and exceptional uniformity.  It looks great in ground beds and would make a beautiful border, but is a great choice to use in containers since it is always in bloom.  This selection remains very compact and has great heat tolerance during the peak of summer temperatures.