Native Plants and Others

It’s common knowledge that the state tree of New Hampshire is the white or paper birch (Betula papyrifera) while its state flower is the purple lilac (Syringa vulgaris.) The birch, venerated for its white bark and flexible but resilient “bend but don’t break” manner, is a hardy native, and one which stands out year round. The lilac, on the other hand, is decidedly “not from around here”, but rather an exotic species of southeastern European origin, having been brought by early settlers to Portsmouth, NH and then distributed far and wide. Despite its having existed in North America for over 300 years, it will never be a native, even though it has become naturalized (a term which is applied to both plants and people. In a way, most of us are all naturalized citizens.)  Its presence is often only revealed in spring, when its fragrant and familiar blossoms betray its position, one which once probably began in the dooryard of a colonial home long gone, its cellar hole a vestige of time past, as suggested by Robert Frost (another non-native – he was born in California) writes in his poem “Directive”:

...for the house that is no more a house,

But only a belilaced cellar hole,

Now slowly closing like a dent in dough. 

Lilacs, courtesy of April Walker

I compare the birch and lilac because they represent more than the official state flower and tree. They also illustrate the problem with declaring natives more suitable than exotics in the landscape.

Native plants (the definition of which varies, but typically used to describe those which were here before European colonization – but that is also problematic, as there were trees growing millions of years ago on this continent which are only found today in Asia) are thought to be better choices for the landscape, requiring less water and other care than exotics. There are plenty of Japanese Barberries, Norway Maples, Burning Bushes, and other plants which have escaped from cultivation and are now considered invasive species to disprove the thesis.

Let me state that I am a firm believer in the value of native plants, appreciate their beauty and status in the wild, and am a dedicated advocate for their use in managed landscapes whenever appropriate. Given the choice between a native and an exotic, I will typically opt for the former. However, as shown in the above example, exotics also have their place, so long as they don’t spread so aggressively as to displace native plants which have evolved along with native wildlife to their mutual benefit.

Drive down a country road when lilacs are in bloom, and you are likely to see lilacs growing as described by Frost, Whitman and others, an enduring and endearing shrub which has become an archetype many homeowners can’t live without in their gardens, despite its brief display. The white birch, on the other hand, is easy to spot at any time, but much harder to grow. It prefers cool, moist soil, and suffers when affected by drought. Indeed, its major nemesis is an insect called the Bronze Birch Borer which is able to detect a chemical signal emitted by birches under stress, and in which she lays her eggs which hatch and spell doom for the tree.

A similar example can be found with dogwoods: the native flowering dogwood (Cornus florida) is susceptible to another form of borer, as well as a destructive disease, when not grown under the right conditions. The exotic Kousa dogwood (Cornus kousa) is resistant to both, and is often the better choice. Hybrids between the 2 species (the so-called Rutgers types) have been produced which offer the best of both.

Clearly, the discussion of whether native plants are superior is complicated. Natives usually offer wildlife more value, and their presence in natural settings is critically important. However, it bears notice that natives may not always work well in managed landscapes, and appropriate choices may be found in plants which may not have originated here.