Superior Herbaceous Perennials from Colorado State University

By James E. Klett, Ph.D., CSU Professor & Extension Landscape Horticulturist; & David McKinney, CSU Undergraduate, Horticulture Major

Research continues on evaluating herbaceous perennials at our new perennial demonstration, research and teaching garden located north of University Center for the Arts, which was moved to this site in 2016. We had very good survival (approximately 90 percent) after moving the plants from the Plant Environmental Research Center (PERC). Additional watering was given to this garden during the winter of 2016-17, and some liquid feeding was given to perennial plants during the 2017 season.

The following eight perennials (some new—some older) had outstanding appearance and performance during the 2017 growing season. If you desire more information about these or any other perennial in the trial, go to and select “Perennial Results” under the “Trials” tab.

Agastache ‘John Pair’ – ‘Kudos Silver Blue’ PP 25,344 – KudosTM Silver Blue Hummingbird Mint from Terra Nova®

The lavender blue flowers, which emit a minty aroma, sit above silvery green foliage, and cover the plant from mid-summer to first frost. The growth habit is low and spreading about two feet in width and eight to 12 inches in height. Little deadheading is needed and the plant is drought tolerant and attracts pollinators.

Achillea millefolium ‘New Vintage Violet’ – New Vintage™ Violet Common Yarrow from Darwin Perennials

Violet purple flowers fade to light lavender over silvery green, fine textured, ferny foliage from mid-summer to first frost, especially having new flower flushes after deadheading. The growth habit is upright with flowers reaching 18 inches in height, and the full plant reaching two feet across. It is a vigorous grower, fills in quite quickly, and has semi-drought tolerance.

Agastache ‘Rosie Posie’ PP 25,857 – Rosie Posie Hummingbird Mint from Walters Gardens/Proven Winners

Pink to purple flowers blanketed this plant from mid-summer until first frost. It has a mounding growth habit, maturing to about two feet tall and wide. This plant is a favorite for some pollinators and has some drought tolerance, but needs some extra moisture during dry winters.

Geranium ‘Gerwat’ PP 12,175 – Rozanne Cranesbill from Monrovia

This plant has been a favorite for years, and performed exceptionally well again in 2017. It was the Perennial Plant Association Perennial Plant of the Year in 2008. The purple to pink or fuchsia flowers, which cover the plant from mid to late summer to first frost, sit atop good green foliage. The growth habit is mounding to spreading with height to about 18 inches and spread up to three feet. It is a favorite for pollinators, has vigorous and hardy growth, and fills in quickly.

Hibiscus ‘Heartthrob’ – Heartthrob Hardy Hibiscus PP 24760 from Walters Gardens/Proven Winners

The scarlet flowers reach close to 12 inches across, rise above good green foliage with a red tinge, and adorn the plant from late summer to first frost. The growth habit is upright mounding, maturing to about four feet tall and three feet wide. This hibiscus is very vigorous and hardy, and survives Colorado winters well.

Phlox ‘Barsixtyone’ PP 22,223 – Flame™ Violet Garden Phlox from Bartels

The plant is covered with violet flowers from early summer to first frost, and blooms heavily after deadheading, above waxy green foliage. It has a strong, upright growth habit, growing to a height and width of about two feet. Butterflies seemed to love this plant and it was bred for resistance to powdery mildew.

Panicum virgatum ‘Cheyenne Sky’ PP 23,209 – Cheyenne Sky Switchgrass from Walters Garden/Proven Winners

The growth habit of this grass is upright with a height of three feet and width of two feet. The foliage is green with hints of red and good reddish fall color. The growth habit remains upright into the winter. The pink blooms start in late summer and persist into the winter, and the plant is quite drought tolerant.

Veronica x  ‘Sunny Border Blue’ – Sunny Border Blue Speedwell from Bluestone Perennials

This plant is covered with blue to purple flowers from mid-summer to heavy frost, above dark green foliage. It has an upright growth habit, growing to a height of about 18 inches and spread of two feet, with strong stems. It is semi-drought tolerant and continues to bloom well after deadheading.