Native Plant Cultivars Gone Good

American chestnut, Some rights reserved by Jami Dwyer

This past June I tackled the thorny topic of native plant cultivars.  Native plant enthusiasts have a broad spectrum of opinions about these versions of native plants, selected and bred to suit the needs and/or desires of gardeners.  In that earlier post, I talked about some of the ways that these native plants may suit people but fail to suit the needs of our wildlife.

In the comments to that post, Beatriz Moisset made a wonderful observation which caused me to immediately start kicking myself for not including a discussion of it to begin with:

“One case in which cultivars are not only justified but a necessity is when the native species is going extinct because of an introduced invasive pest. I am all for creating cultivars of elms, American chestnuts and hemlocks. That is probably the only way to save them from Dutch elm disease, chestnut blight and hemlock woolly adelgid.”

Beatriz did, indeed, highlight and important aspect of native cultivars:  they are not always designed to benefit humans exclusively.  Through the rampant, and sometimes careless, transport of exotic plants from one continent to another gardeners have occasionally introduced pests which devastated once-important populations of native trees.

As detailed in the fabulous book American Chestnut: The Life, Death, and Rebirth of a Perfect Tree, chestnut blight was one of the first well-documented cases of this in the United States:  William Murrill noticed a pathogenic fungus from Asia began killing American Chestnut (Castanea dentata)  in New York in 1904, and by the 1940s this once important species had been virtually extirpated from its natural range.

There are isolated stands of American Chestnut which had been planted by settlers, which have so far been spared infection by the most virulent strains of the blight.  And researchers are working hard to develop blight-resistant cultivars of Castanea dentata, either by identifying naturally resistant trees or by hybridizing American Chestnut with Chinese chestnut trees.  These cultivars, if successfully developed, will play a crucial role in reintroducing this important species to our forests.

In the meantime, I encourage people to plant the straight species anyway.  Although these non-resistant trees will eventually succumb to blight, they do not tend to die completely.  Rather, the blight causes them to die back to the ground and then re-sprout.  These trees never gain the beautiful form of the unaffected trees, but they still provide some of the wildlife value they are meant to provide.  And supporting the research in developing the American Chestnut cultivars strikes me as a worthwhile endeavor.

Princenton Elms planted near the White House, in Washington D.C. Image courtesy Casey Trees.

In some ways, the iconic American Elm is an even more hopeful case.  This stately tree, once severely threatened by the imported Dutch Elm Disease (DED), is most certainly on the rebound in cultivated landscapes.  There are several DED-resistant cultivars available today.

The Princeton Elm is one of the best known and most widely sold.  This cultivar was originally selected for its beautiful vase-shaped form, and was subsequently observed to be DED-resistant.  As a result, it is becoming much more commonly used as a street tree just as the American Elm had been before the 1960s.

The Valley Forge Elm is another widely available variety of DED-resistant American Elm.  Most reports suggest the Valley Forge is even more resistant than Princeton, but it tends to require more attention to pruning and training when young than the Princeton.  Other cultivars of American Elm are being trialed, and I generally advise the use of multiple cultivars in landscapes where that genetic diversity is aesthetically acceptable.

I’ve just barely scratched the surface of these “beneficial” cultivars, but I want to point out three more things.

One is that both the American Chestnut and American Elms are cherished not only by people, but also by wildlife.  The chestnuts are an important source of protein for wild animals, and both species are important larval host plants supporting hundreds of species of butterflies and moths.  In some cases, they are unique hosts so including these species in native plantings within their native range is critical even if they don’t have perfect survivability.  And the selective use of disease-resistant cultivars can allow us to include these species in managed landscapes.

American Elm

Ulmus americana, image © Robert O’Brien

The second is that in both cases, landscape specimens of these native trees played a crucial role in the survival of the species.  It DOES matter what we plant along our streets, in our parks, and at our homes.  Creating metapopulations of rare and/or endangered plants is important, but it is also important for us to maintain a stocks of native plants in places where we can observe them closely:  you never know when the next imported pest will threaten a cherished native species and by keeping these species close by we can maximize the chances of saving them should it happen.

And the third is that it DOES matter that we maintain a genetically diverse gene pool of native plants.  Different plants react differently to pathogenic threats, so it is important that we not overplant any single species and especially important that we not overplant any single cultivar of a species.  There are many native plants that, for all intents and purposes, exist in the horticultural trade as a single widely planted cultivar.  Viburnum dentatum ‘Blue Muffin’, Rudbeckia fulgida ‘Goldsturm’, Panicum virgatum ‘Shenandoah’, Crataegus viridis ‘Winter King’, Physocarpus opulifolius ‘Diablo’, and so on. Seeking out and planting straight species or, at least, a variety of cultivars, seems like wise insurance.

© 2011 – 2013, Vincent Vizachero. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.

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  1. says

    Vincent, as always you provide so much food for thought. You’re right, it IS important to think about what we plant, not only for our own desires, but also for their value to wildlife and impact on the ecosystems. Thanks for pointing out the value of these cultivars and their benefits to wildlife. It’s nice to know that so many people are working so hard to promote these native trees, protect the gene pool, and also develop strains that are resistant to the diseases that have come so close to wiping their existence out.
    Carole Sevilla Brown recently posted..Shop Small, Shop Local

  2. says

    Vincent, very good points! Where we must do cultivars, I like the idea of promoting as much diversity as possible. This is helpful to me because as a small nature preserve with very limited budget we have a very hard time buying seed for local-genotype plants where we can’t gather and propagate the seeds ourselves.

    Also, could we hope that some day, when testing new “necessary” cultivars like those of the American elm, that they test the trial cultivars to see which ones are most acceptable to the native insect population?

    • says

      I’d love to see more effort put into cultivars based on geography and/or wildlife support. I often find myself to be lucky living in Maryland, since many cultivars are selected from nearby areas like PA or NJ. If I know the provenance of a particular cultivar, and it is within (say) 150 miles of my house I feel a lot better about it.
      Vincent Vizachero recently posted..A Native Plant Flower Show!

      • says

        the take away I got out of your article, for conservation restoration, is that cultivars are an acceptable choice when the local genotype is gone and and then it’s best of use several cultivars to give nature a chance to make a new local genotype. Agree?

  3. says

    Vincent I also like variety and diversity in my garden so I choose many different winterberries or viburnums for example. Rudbeckias well I love to try new cultivars…happy to hear the Chestnut and Elm are back. If I were to replace a tree that may go down, I would choose an oak first…great food for thought!!
    Donna@Gardens Eye View recently posted..Health

    • says

      Donna, thanks for the comment. It’s an interesting dilemma: I do love oaks because of their high wildlife value, but there are already so many oaks in the landscape that I sometimes wonder if adding one more rare plant (like an elm or a chestnut) is doing more good than adding one more oak (of which there are already many). Or not.

      As you say, it is food for thought.
      Vincent Vizachero recently posted..A Native Plant Flower Show!

  4. says

    Thank you for the update. I am glad that you did such good research on the subject and I am happy that you discussed metapopulations; a very important subject that we should all keep in mind.
    I just want to add that according to the Hosts website of the Natural History Museum, 92 species of moths feed on Castanea dentata, and more than 200 feed on Ulmus americana. It seems like enough caterpillars to keep many nesting birds happy.
    Beatriz Moisset recently posted..Bees and vitamins

  5. says

    I’ve been planting straight species Rudbeckia fulgida and…well, I gotta admit, they did a helluva job with “Goldsturm.” I’ve got the species tucked in an area where it does pretty well, it’s a nice enough plant but “Goldsturm” is the real showstopper in the yard. While I know that we need those straight species for diversity purposes, and I’m glad to be able to plant them, I can understand why the nursery trade is dominated by some of those cultivars.

    The Viburnums, however, are particularly obnoxious because the bloody things are all self-sterile, and the big selling point about “Blue Muffin” is berries that you don’t get without something OTHER than “Blue Muffin.”
    UrsulaV recently posted..Fuzzy-Wuzzy

  6. says

    Worth mentioning, an update on the American chestnut saga:
    Also I have been pondering about how the functional extinction of this species affected pollinators. I found one interesting reference going back many years. Honey production nearly collapsed after the disappearance of the American chestnut in Appalachia. Ha! And many think that the honey bee problems started only recently. I am writing an article on the subject.
    Beatriz Moisset recently posted..Monarchs and their Enemies


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