What a beautiful autumn!
As I write this column on the evening of October 20, a succession of sunny days and cool nights without a killing frost has developed rich colors in the leaves of native shrubs and trees, hues that are atypical for some species. For example, the leaves of the mapleleaf viburnums (Viburnum acerifolium) in Marjorie’s Garden have turned a deep pink color, redder than the salmon-pink of past autumns, while a mountain maple (Acer spicatum) at the back of the garden has leaves of pumpkin orange for the first autumn in its 12 year history.
The leaves of summersweet clethra (Clethra alnifolia) are turning, some now bright lemon yellow, others still showing some green. As time goes by, the yellow leaves will tarnish with freckles of brown.
Of the three native plant species mentioned above, only one, summersweet clethra, can be readily obtained at local garden centers and nurseries. Mapleleaf viburnums and mountain maples are sold only by obscure mail order nurseries that specialize in native flora and they are typically available only as small seedlings. As I strolled through the garden this morning, I recalled the history of these two native species in Marjorie’s Garden.
The mapleleaf viburnums, now over 5 feet tall, were dug as slender seedlings less than a foot tall from a research site in Boothbay, Maine, back when I taught woody plants and conducted research on invasive plant species at UMaine, Orono. A graduate student and I wanted to determine if an invasive species in the area, burning bush (Euonymus alatus), was altering soil pH where it was growing, as other invasive species are known to do. We needed a control, a native shrub species that was growing alongside burning bush at the Boothbay site, and we chose mapleleaf viburnum. We wanted to conduct the experiment in Orono and so we dug and potted several small seedlings of both species from beneath the tall canopy of white pines at the Boothbay site. When the experiment was completed, the viburnum seedlings were rescued from the compost pile and planted in Marjorie’s Garden.
Over the past twelve years, we have found mapleleaf viburnum to be a durable shrub, even with the viburnum leaf beetle in the picture. We enjoy the clusters of tiny white flowers in spring, including the myriad pollinating insects that they attract, as well as the heavy fruit set – a favorite of birds – in summer.
The mountain maple in Marjorie’s Garden was grown from seed collected over 12 years ago from a single tree growing at the same Boothbay site. I first saw the tree at dusk on a spring visit to the research site. It was in full flower, lighting up its corner of the woods with upright candelabra-like clusters of greenish-yellow flowers. I returned to the site later that summer with the intent of collecting seed, only to find the tree nearly destroyed by timber harvesters dragging pine logs out of the woods; just one of the original three trunks had survived to mature a handful of seeds on its branches. I collected these seeds and successfully produced seedlings, one of which now graces the back of the garden. Over ten feet tall, it has been producing its own seed for several years.
I tell these two short stories to illustrate how difficult it is to find sources for many garden-worthy native trees and shrubs. Few gardeners have the opportunity to rescue plants from terminated research projects or to successfully propagate woody plants from seeds. For most gardeners, there is no source for plants like mountain maple, mapleleaf viburnum, and other garden-worthy native plants.
It should be otherwise. As the combined impacts of habitat destruction and invasive species continue to forever change areas where native plants once thrived, gardens can offer refuge for those native species, places where the plants and the animals that depend on them can thrive.
Peter Del Tredici, Senior Research Scientist at Harvard University’s Arnold Arboretum, recently pointed out that invasive species are here to stay and that, in fact, they play a useful role in urban landscapes where continued human disturbance creates habit in which only invasive plants can succeed (read an interview with Del Tredici at http://landscapeurbanism.com/article/peter-del-tredici/). But Del Tredici is quick to point out that our gardens should not be havens for invasive plant species. Indeed, our gardens should be refuges for native species, plant and animal.
Del Tredici’s perspective on invasive species is not entirely new thinking. In 1991, well-known author Michael Pollan published a book, Second Nature, which contained the essay, “The Idea of a Garden”. In this essay, Pollan suggests that the concept of wilderness as any place untouched by human influence is no longer viable. Wilderness is dead because no place, no matter how isolated, can be considered immune to the threat of invasive species. Wherever a bird can drop a seed…
In other words, to keep a place wild, we must manage it, scouting for and eliminating invasives. Every sacred place has become a garden, a place tended by gardeners to keep it sacred.
But the sad reality is that the gardeners have given up hope in some of these once-sacred places. Good examples of this hopelessness are in our National Parks. While every National Park has a mandate to keep invasive species out of their domain, the sad fact is that there will never be enough funds allocated to accomplish this mandate. I have seen places in Acadia National Park where Oriental bittersweet has changed the landscape forever. The garden has been destroyed.
With this in mind, why does it remain so difficult to purchase native woody plants like Acer spicatum, Viburnum acerifolium, or any of dozens of other native trees and shrubs with outstanding ornamental attributes? When will the nursery industry start propagating these plants instead of Norway maples, Japanese barberries, burning bush, and other invasive species?
The answer, I think, is that the industry will not change until the demand for native species is far greater than it is now. Hopefully that demand is growing and will continue to grow as more and more gardeners look upon their gardens as refuges.