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Kim Eierman

Kim Eierman

Founder of EcoBeneficial!

Available for virtual and in-person landscape consulting, talks and classes.

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Native Plant Research at the Mt. Cuba Center with George Coombs

Great garden plant or garden slacker?  This is a question that the Mt. Cuba Center in Hockessin, Delaware has sought to answer, giving gardeners and green industry professionals a helping hand in selecting native plants.  Since 2002, Mt. Cuba, has conducted native plant research in their trial gardens, examining native species, native cultivars/selections (“nativars”) and hybrids to evaluate which plants perform best.  Their research has focused mostly on garden-worthiness, namely aesthetic factors, but Mt. Cuba has now embraced ecological research as well.

George Coombs - Research Horticulturist at Mt. Cuba Center

George Coombs – Research Horticulturist at Mt. Cuba Center

The Mt. Cuba Center

Mt. Cuba Center is a unique place well worth a visit.  Located near Wilmington, it was the expansive estate of Mr. and Mr. Lammot du Pont Copeland, who had a keen interest in the environment and horticulture, especially wildflowers.   The large property operated as a private botanic garden until 2001 when Mrs. Copeland passed away and the garden opened to the public.  A garden with a naturalistic focus, Mt. Cuba features plants that are native to the Eastern United States, and can be visited from April through October.

Trial Garden Process

George Coombs is the Research Horticulturist and manager of the trial gardens at Mt. Cuba.  He spoke with me about the ongoing research, explaining that a trial garden is a common garden experiment examining a variety of different plants within the same genus that are closely related (ex: Echinacea purpurea, Echinacea tennesseensis, Echinacea pallida, etc).  Grown in the same conditions over a two to four year period, the plants show what they can do – sometimes with great results, sometimes not so great.

Baptisia trial at Mt. Cuba Center

Baptisia trial at Mt. Cuba Center

The trial garden set-up is described by Mt. Cuba as follows:

Two plants of each taxon are grown in full sun in a 15,000 sq. ft. trial garden.  The trial garden is protected from rodents by a 4’ tall wire fence, and is located within a 100-acre garden protected by a 10’ tall deer exclusion fence. The clay-loam soil in the trial garden has an average pH of 6.5.

Plants are watered as needed during the first year in order to get them established.  After that, they are left on their own.  Pesticides are not used unless there is a serious threat to the trial’s survivability.

Mt. Cuba’s goal in their native plant research is to determine which native species, selections or hybrids are best suited for the home garden. Although their focus is on plants suitable for the Mid-Atlantic, much of their research is relevant for other regions of the country, particularly the Northeast and the Southeast (keep hardiness, heat zones and soils in mind).  After a given plant trial is completed, Mt. Cuba publishes the results in a comprehensive report which they publish on their website.

Baptisia australis 'Big Ben' with happy bumble bee

Baptisia australis ‘Big Ben’ with happy bumble bee

Evaluation Criteria for Native Plant Research

The criteria for evaluation for any given trial can vary based upon the plant group.  Coombs explained that their ongoing trial of Monarda is evaluating resistance to powdery mildew, plant hardiness, plant habit and nectar availability. This new research focus on nectar and pollinators is especially exciting – a joint effort with the University of Delaware.  Dr. Deborah Delaney, Assistant Professor of Entomologist, heads the pollinator research in conjunction with Owen Cass, a Mt. Cuba Center Fellow.

Pollinator Research at Mt. Cuba

Owen Cass, Mt. Cuba Research Fellow, researching nectar

Monarda Research Trial

The Monarda trial is running for three years at Mt. Cuba, from 2014 to 2016, after which a report will be issued with final results.  Forty-three species, cultivars and hybrids of Monarda are being examined, ranging from cultivated garden favorites to more obscure natives.  While the research is still early in the game and final scores are not in, some of the standout plants in the first year include three species of Monarda:

Monarda citriodora

Monarda citriodora

Monarda citriodora (Lemon Bee Balm), a 1 to 2 foot tall plant with lavender or pink flowers, native to parts of the Southeast, Midwest and Southwest.  A magnet for native bees, butterflies and hummingbirds.  Tentative Mt. Cuba score: 3.9

Monarda punctata (Dotted Horsemint), an unusual biennial Monarda with lavender bracts and yellow flowers spotted with purple.  This is another plant noted to be of special value to native bees and honey bees by the Xerces Society.  Tentative Mt. Cuba score: 3.5

Monarda punctata

Monarda punctata

Monarda clinopodia (White Bergamot or Basil Bee Balm), also of special value to native bees, sporting a late summer bloom in white or pink, often found in nature in part shade. Tentative Mt. Cuba score: 3.4

George Coombs mentioned two Monarda hybrids that are also doing well in the trial:  Monarda ‘Prairie Gypsy’ a hybrid of Monarda bradburiana and an unknown parent, sporting numerous light purple flowers (tentative rating: 3.4) and Monarda ‘Grand Marshall’   A petite plant with magenta flowers (tentative rating: 3.5).

Monarda 'Grand Marshall'

Monarda ‘Grand Marshall’

Current results of the Monarda trial are available on the Mt. Cuba website.

More Plants or Better Plants?

Some of the plant trials at Mt. Cuba are enormous. The Heuchera (Alumroot) trial included an astounding 87 plants, indicative perhaps of the great popularity of the plant, and perhaps too many introductions. The market for plant introductions can be fast moving and overly-saturated. Coombs mentioned that the Echinacea trial report, published in 2009, is now somewhat out-of-date since so many of the plants in the study are no longer available for purchase. Apparently the same zeal for new plants has not existed for Asters – Coombs noted that the 2006 Mt. Cuba study on Asters (their first native plant research report) is still quite relevant.

Heuchera villosa

Heuchera villosa

Coombs offered his wise observation that “new is not always better… we can get distracted by plants that are new.”  He added that many garden favorites, the tried and true plants, are usually great performers.

Other research trials at Mt. Cuba include those on Baptisia, annual Coreopsis, perennial Coreopsis, and Phlox (just planted in 2015). Coombs is considering new research trials on Blueberries as well as Hydrangeas.

Podcast Interview with George Coombs

Vaccinium corymbosum

Vaccinium corymbosum

Check out all of the research from Mt Cuba to see what plants might deserve a place in your garden.  And, listen to my podcast interview with George Coombs to learn more.

From Kim Eierman at EcoBeneficial!

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