Practices and processes for plant trials have changed, but the benefits of perennial trials are as relevant as ever.
Photo courtesy of Longwood Gardens

If you look back 10 or 20 years at how plants were trialed in the U.S., you would find that public horticulture institutions and botanical gardens traditionally played a more critical role in plant introduction. Such independent institutions delivered what was considered to be unbiased recommendations to regional growers who then took that under advisement when deciding which varieties to produce. Founded in 1932, All-America Selections is the oldest plant trialing organization in the country, and it includes a network of trial gardens across the U.S. to provide a good representation of all growing conditions.

Plant trial evolution.

In her University of Delaware thesis, “Evaluation of Trial Garden Practices at Public Horticulture Institutions,” completed in the spring of 2015, Sarah Leach Smith noted that field trials have experienced a significant shift during the past five years. Through extensive surveys of growers, breeders and public trial gardens, Smith found that the size of plant trialing programs has actually increased, but the amount of plant material sent to public gardens has decreased.

Instead, breeding companies are opting to send trial material directly to potential grower customers for production and in-ground trials. 

“With commercial grower trials nationwide, the regional performance data provided by university or public garden trials is no longer as crucial; the wide geographic range of commercial trials fills that need for most breeding companies,” says Jim Nau, manager of The Gardens at Ball (Smith, 2015).

The value of grower trials.

Paul Westervelt, annual and perennial production manager at Saunders Brothers, reported that the best perennial trials he sees with any regularity are those of his plug vendors. However, since Saunders Brothers typically ships most of their product within their own region, their own in-ground and production trials are especially valuable. 

“Our whole group is trialing some of the same products and comparing notes to see how things do. The combined efforts of the group will yield much better information than any one trial site because of our different climates, allowing all of us to bring products to market more confidently and bring assurance to our customers,” he says.

Denise Kelly, planning and trial manager at Smith Gardens explains, “We’ve been doing our own trialing since 2009, and we currently trial about 1,500 different varieties of annuals and perennials. Performing trials at our own facility gives us the knowledge we need for preparing our production team for new genetics that will be going to market potentially two to three years ahead of production.”

A few of the most notable trial gardens in the country, including the Chicago Botanic Garden, see great support from breeding companies and growers. Richard Hawke, plant evaluation manager and associate scientist at the CBG, says he usually receives plant material to trial as new varieties are being introduced or shortly thereafter. He adds that one local grower, Elite Growers, references the trial information and ratings from his trials in their wholesale catalog.

Westervelt wisely points out that it is virtually impossible for any grower or institution to trial everything, so it is crucial to network with others, share observations and learn from one another’s work. I spoke to key trial managers and growers at public institutions, botanic gardens, and grower facilities to get their take on a few perennials that have stood out to them over the last few years as must-haves. They also shared which perennials they think more people should be growing in their region.

Q: Tell me about a few perennials that have really impressed you in your trials over the last few years.

Zone 5b: Richard Hawke, Plant evaluation manager and associate scientist, Chicago Botanic Garden

June Hutson of the Missouri Botanical Garden Zone 6b recommends Amsonia ‘Blue Ice’ as a low maintenance groundcover that blooms longer than typical blue stars.
Image courtesy of Susan Martin

A massive number of perennials are trialed every year at the CBG, but inevitably a few favorites rise to the top. Baptisia Decadence ‘Lemon Meringue’ is one of those standout perennials.

“I love the beautiful bright yellow flowers on dusky stems—it’s an eye-catching combination. We’re growing this variety in our trials and on our green roof, where it has excelled for the past three years. It’s almost as large there as plants in the ground trials.”

Sapphire Indigo clematis is another favorite of Hawke’s because of its “insane flower power.” This non-climbing selection is covered in large, deep purple-blue flowers from June to September in the Chicago trials. Agastache ‘Rosie Posie’ was another star of the 2015 trials, blooming endlessly with bright rosy pink flowers and magenta calyces. Hawke reports that it has survived its first winter in the trial garden.

Zone 6a: Jeremy Windemuller, Trial manager, Walters Gardens; owner of Windridge Perennials and Landscaping

Windemuller has been extremely impressed with Hibiscus ‘Midnight Marvel,’ one of the first hardy selections with dark foliage and a great compact size of 3-4 feet. This plant shines when so many others are struggling from the summer heat, producing large 8-9 inch, red flowers from top to bottom due to its indeterminate bloom habit.

“I have found it very easy to grow perennial hibiscus using bare root plants to produce 2-3 gallon finished plants in just 8-10 weeks with flowers in 12-14 weeks.”

Zone 6b: June Hutson, Supervisor of Demonstration Gardens, Missouri Botanical Garden

Richard Hawke in Zone 5b says Pycnanthemum muticum is an underused perennial that is great for attracting pollinators to the garden.
Photo courtesy of Chicago Botanic Garden.

Lesser known perennials such as Amsonia ‘Blue Ice’ and Kalimeris incisa ‘Blue Star’ have impressed June Hutson and her team at the Missouri Botanical Garden. ‘Blue Ice’ makes a terrific groundcover as it is one of the only spreading types of Amsonia, and it blooms over a longer period than most. ‘Blue Star’ is a good choice for rain gardens and is long blooming too.

Zone 8a: John Ruter, Professor of horticulture and trial gardens director, University of Georgia-Athens

Ruter is impressed by the vibrant yellow bloom power of Baptisia sphaerocarpa ‘Screamin’ Yellow’ every spring, and likes that it is more compact than many other Baptisias. The new Cannova Cannas have been impressive as well, overwintering well for them in-ground. Setcreasea pallida ‘Blue Sue,’ which is an annual in most zones but a perennial at UGA, is another interesting and versatile plant favored by Ruter.

Q: Tell me about a perennial that doesn’t get the attention it deserves in your climate. Why should people be growing it?

Zone 3a: Owen Vanstone, Owner of Vanstone Nurseries, Manitoba, Canada

“I love Penstemon barbatus ‘Clearly Coral.’ It is not well known but is very hardy and puts on a terrific display.” This Zone 3 hardy cultivar was developed in Manitoba and has demonstrated excellent hardiness and vigor in the Prairie landscape.

Zone 4a: Neal Holland, Retired horticulture professor and owner of Sheyenne Gardens near Fargo, N. D.

Holland raved about Nepeta ‘Dropmore,’ which he explained is far superior to ‘Walker’s Low’ in their climate. It has good winter hardiness, is very long-lived and does not self-seed around the garden. Agastache ‘Blue Fortune’ and Anemone sylvestris were also named by Holland as perennials more people should be growing in Zone 4.

Zone 5b: Richard Hawke, Leave it to Hawke to come up with an amazing-yet-overlooked perennial for Zone 5 gardens. Pycnanthemum muticum, commonly known as short-toothed mountain mint, is a great plant for attracting pollinators to the garden.

It may not be the newest carex on the market, but John Ruter at the University of Georgia says ‘Evergold’ is one of the most reliable in their hot, humid climate.
Image courtesy of Susan Martin

“When its tiny pink flowers are in bloom in mid- to late-summer, they are teeming with a variety of butterflies, moths, bees, and beneficial wasps—not for anyone afraid of flying insects. But the trait I like best about this mountain mint is the silvery leaf-like bracts that sit under the flower clusters. The entire plant looks like it’s covered in frost when it’s in bloom, and the fragrance and texture of the fuzzy bracts is awesome too.”

Despite being touted as having a vigorously spreading habit, it was the least rhizomatous of the mountain mints he has trialed.

Zone 6a: Jeremy Windemuller, New shade perennials can be hard to come by, and Aralia cordata ‘Sun King’ is one of the best introductions Windemuller has seen in recent years. Its bright yellow foliage has a tropical look but the plant is actually very hardy down to Zone 3. “One thing I really love is that it is deer resistant. That’s a plus when the deer tend to want to mow down a shade garden.”

Plant it where it will receive morning sun or filtered sunlight throughout the day to maintain its glowing yellow color.

Zone 6b: June Hutson, Hutson believes from her experience working at the Missouri Botanical Garden that more people should be growing bush-type clematis. They use them as groundcovers in the gardens there. She specifically recommends C. integrifolia ‘Rose Colored Glasses’ for its beautiful blooms.

Zone 8a: John Ruter, Though newer forms have become available, Ruter still recommends Carex h. ‘Evergold’ for its reliable performance in containers and landscapes even in the Georgia heat, though it does need protection from hot afternoon sun there. Another plant Ruter recommends for its great heat tolerance is Cuphea micropetala, which has good color going into the fall months.

UGA is breeding for Hibiscus moscheutos cultivars with sawfly resistance, and also has breeding programs for agapanthus, liriope, stokesia, heliopsis and pavonia.

These recommendations are just the tip of the iceberg. Make the time to talk with a trial manager in your local area to find regional rock stars to add to your lineup. Sending plants to trial in public gardens should be a crucial piece of a breeder’s or plant introduction company’s marketing plan, a pull-through effort to educate the public and create demand for the best varieties for specific regions.

Susan Martin specializes in horticultural marketing, content generation and management, and working with green industry clients in trade and consumer sectors.