High Country Autumn Perennials By Vaughn Fletcher

These established varieties displayed superior performance at Colorado State University’s trial garden.

The focus this month is the Colorado State University (CSU) perennial trial, which I have had the opportunity to visit for many years. This is one of the most beautiful trials in the country, located in downtown Ft. Collins within the university campus.

I attend the flower and perennial trial in early August and return again later in September, before the snow flies, to evaluate performance and specifically summer hardiness and floriferousness. The perennials highlighted were still at their peak in late September.

The CSU annual flower trial garden is an official All- America Selections display garden and trial ground. The perennial demonstration garden is adjacent to the flower trial and was established in 1980 by Jim Klett as a teaching tool for the university horticulture program. The garden comprises over 1,000 different taxa, and new introductions to the program are tested for three years before becoming a part of the permanent display.

The perennials in this article are part of the established collection and have demonstrated superior performance. They are adaptable and used in perennial programs throughout the industry.

Walters Gardens

This compact, mounded cultivar was the most floriferous agastache in the trial. The bicolor flowers of hot pink, complemented by magenta-purple calyxes, were impressive and well positioned above the foliage to create a colorful canopy from midsummer through fall. The green minty foliage is aromatic, and the plant matures at 24 inches. A butterfly and hummingbird magnet, it is listed as Zone 6 by Walters but is performing in Colorado in Zone 5b.

Must Have Perennials

This compact series has been in the marketplace for many years and continues to provide outstanding color for late summer through fall. There are five colors available and Lady Susan with rich pink single blooms has the largest flower in the series. It is recommended for partial shade but was in full sun in the CSU trial and manifested a prodigious flower canopy. The series is deer and rabbit resistant and is utilized in fall perennial programs with pansies and mums. The series matures at 18 to 20 inches and is hardy in Zones 5 through 9. Vernalization not required for flowering, but long days are imperative for flower initiation.

Must Have Perennials

One of the most colorful perennials in the trial was aster ‘Vibrant Dome’. This sport of ‘Purple Dome’ manifested a prolific flower canopy of semi-double, vibrant hot pink, star-shaped flowers with a compact, mounded habit. This variety matures at 18 to 24 inches is durable and mildew resistant. It is hardy to Zone 4. Staking is not required, and it enhances the autumn color palette with striking color.

Must Have Perennials

This hardy mum was one of the most colorful plants in the trial garden last fall with masses of deep pink, button flowers. This series is comprised of 15 varieties including spider, button and decorative flower types. They add outstanding late summer and fall color, maintaining a uniform, compact habit. The plants are excellent in mass plantings and mixed borders with an abundance of flowers creating outstanding impact. The series is hardy to Zone 5, first year flowering and mature at 18 to 24 inches. The plants are larger and earlier flowering when established following the second season in established beds. The blooms will continue until frost providing much needed color at that time of year and extended performance for the consumer.


This variety is native to the Great Plains and is naturalized throughout much of the United States. In the CSU perennial garden, the plants were covered with hundreds of yellow ray flowers with darker yellow center disks. It blooms profusely in late August, September and October. It has limited application because of its vigor and ultimate height of 3 to 8 feet. Thriving in naturalized ecosystems, it is an excellent food source for bees, birds and butterflies in the fall. This variety is hardy to Zone 4, and if you need a native plant for naturalization in a back ground setting, this variety with dramatic architecture and outstanding flower power fits that requirement.

Terra Nova Nurseries

This genus comprises 60 to 70 species and many hybrids. One of the most impressive is the Popsicle series which has been in production for many years and continues to perform in early summer through fall with long terminal racemes of tubular flowers that are dramatic in the landscape or when utilized in mixed containers. The spikes will continue to produce flowers successively positioned well above the foliage canopy. The series features eight vibrant colors with compact grass like foliage maturing at 12 to 15 inches. This award-winning variety provides dramatic mango-orange blooms that are unique and eye catchers. Popsicles have multiple applications in mixed beds, mass plantings and vertical accents in containers. They are hardy to Zone 5, extremely drought tolerant, and a hummingbird magnet.

Darwin Perennials

English lavender had been an integral part of herb gardens for many years. This award-winning variety has many attributes, including large deeply saturated blue flowers on short pedicels, intense fragrance, and heat and drought tolerance. The flowers are stacked, creating excellent color impact. It is heat and humidity tolerant, maturing at 12 inches and hardy to Zone 5. This is an outstanding lavender for containers, borders and rock gardens. The rich, large blooms with short flower spikes and durability of this cultivar set it apart from other angustifolia varieties.

Dümmen Orange

On this specific day in late September leucanthemum ‘Sweet Daisy Christine’ was extremely eye catching with brilliant white single flowers with yellow centers. This cultivar in production is early and first year flowering. It is naturally compact, maturing at 10 to 12 inches. It is hardy to Zone 5 and more vigorous in beds with excellent upright sturdy branching. There are many outstanding leucanthemum in the market, and this cultivar is deserving of consideration in your program.

Dümmen Orange

There were many phlox cultivars in the trial, and this variety was notable for its stiff, upright stems, large terminal flower clusters and mildew resistance in late September. The Flame series presents 15 varieties, including three new colors for 2018, and has been the backbone of many paniculata programs. ‘Flame Blue’ was compact and well branched with stable blue and white pinwheel flowers. The plants were floriferous and eye catching. The series is hardy to Zone 4, compact, early blooming, and has strong upright branching compared to other varieties. It continued to bloom prolifically through fall.

Walters Gardens

This has been one of the most prolific flowering and stunning tall garden phlox in multiple trials the past few years, and it demonstrated these attributes in late September in this trial. The tubular, fragrant, hot coral-pink florets on terminal clusters are stunning and contrast with dark green foliage and purple stems. ‘Glamour Girl’ begins blooming in mid-July and continues through September. It is hardy in Zone 3 and matures at 2 to 3 feet. The attributes of uptight habit, stem color, prodigious flower canopy and vibrant color contribute to excellent retail presentation and consumer appeal. There are very few paniculata that match this variety in color, vibrancy and visual impact.

Darwin Perennials

This compact, upright and free blooming rudbeckia produced masses of yellow ray flowers with a purple center disk. It had a prodigious flower canopy with an upright habit. The beautiful mahogany foliage created excellent contrast with the flowers. More compact than the traditional Black Eyed Susan, it has multiple applications in containers, perennial borders and naturalistic plantings. It is hardy to Zone 4 and matures at 24 to 30 inches.

North Creek Nurseries

This is the first ornamental grass I have mentioned in my articles, but I could not have chosen a better selection to highlight. This Little Bluestem variety was outstanding in the trial in late September with thick blades and sturdy stems creating a tight upright habit. The foliage was bluish green and purple at the base. I have seen this variety later in the season in other parts of the country, and the foliage color transitions to orange, red, yellow and purple. This grass is native and hardy to Zone 3. It matures at 3 to 4 feet and is extremely low maintenance. It is an important ornamental grass with application as a vertical accent or in mass plantings.


Solidago is a genus of more than 100 species, mostly from North America. This cultivar is from the Wichita Mountains of southwest Oklahoma. It was impressive in the trial with an upright, clump forming habit and dense terminal flower plumes. The tiny daisy-like flowers are profuse and create significant flower power on the upright plumes. The plant matures to at 2 to 3 feet and is hardy to Zone 4. It flowers from late August through October and is attractive to bees and butterflies. It tolerates poor soil, is drought tolerant and performs best in full sun. I have seen this variety at arboretums and landscape sites around the country and performance has been consistent. Even though the flowering window is short, it gives outstanding fall color until frost.

While this article is based on my visit in late September to the Colorado State University perennial garden, it is important to remember the annual container and field trial is planted in late May and remains on display until October. Last year there were 740 paid entries, 60 entries from All-America Selections and 334 entries for containers. If you have not had the opportunity to visit this beautiful trial site, I would strongly suggest you add this to your calendar.

Vaughn Fletcher

Vaughn Fletcher is president of Fletcher Consulting. He has been in the horticulture industry since 1971, working in many areas including landscaping, garden center and greenhouse production, greenhouse and nursery sales and sales management. He can be reached at vfletcher9@gmail.com.