Saturday, September 3, 2011


Sweetgum (Liquidambar styraciflua)
is native to my neighborhood...
            In recent years, gardening with native plants has come into fashion. Again. When Tim and I get asked to design one, we give each other secret little smiles and ask the potential client, “Native to where?”

You may recall that, a few posts ago (“Wind and Weather,” August 17th), I vented my annoyance with the NWS and NOAA for using the word “normal” for their computed 30-year averages. (Check out my new gadget at right, Acronyms Explained.) When I read an exchange in American Nurseryman about regulating “invasive” species—those quotation marks again!—I had a similar reaction. “Native” is as nebulous a concept as “normal.”  

...while Rhododendron catawbiense,
native to western North Carolina,
does poorly on the coast; and...
            I’m not just being supercilious and snotty here. Most people, even when impelled by environmental earnestness, don’t have any concrete idea what “native” means. Newcomers here often consider hybrid azaleas, crape myrtles and gardenias Southern natives. Nope, they all originated in China and/or Japan. Tomatoes, some rhododendrons and hemlocks do come from North America—just not this part of it. In the 500 or so years since first darkening the doors of this continent, Europeans have introduced about 50,000 plant species. These introductions include about 90 percent of our present food crops as well as a hefty slice of the ornamentals pie. And that doesn’t include “exotic” animal species like horses and nutrias; insects like European honeybees, some earthworms, fire ants, and the emerald ash-borer; plant pathogens like Dutch elm disease, chestnut blight, and the fungus responsible for sudden oak death; or human diseases like West Nile virus and avian flu. Makes you think, doesn’t it?  

...and crape myrtles
(Lagerstroemia indica x fauriei)
came from the Orient.
            Over time, many introduced species have interbred with their indigenous counterparts, producing natural hybrids that muddy genetic-origin waters more than a whole university-full of hyper taxonomists. 
            People who really, really want a native garden should buy a large parcel of land and just encourage (and perhaps impose a little structure on) what’s already there. Indeed, I would argue that all “gardens” are by definition artificial, the result of human will worked on the land. 

            Philosophy aside, the flip-side of what makes a species native is what makes one non-native. Except for recent introductions whose provenance is (somewhat) known, it can be really hard to tell who’s whose horticultural daddy. Sylvan and Wallace Kaufman point out in the first three chapters of their excellent book, Invasive Plants (see Good Reads at right), that all “natives” were once successful invaders. 

Trans-Atlantic transport
circa 1670
To illustrate the difficulty inherent in defining “native,” I present a Homo sapiens example. Both Tim and I were born in United States to parents who were also born in the United States. No one from either family (the documented ones, anyway) is indigenous to the eastern U.S. My ancestors hailed from all over Western Europe, and it’s anybody’s guess how they ended up there. Two or three lines of my family had established themselves in North America by the latter half of the 17th century. Yep, I’m certified DAR and UDC (check out that acronym gadget mentioned above). But am I more native than Tim? Both sets of his grandparents sailed from Ireland in the 1890s, some 220 years after my folks got here. Besides, with all due respect, even the “Native Americans” came from somewhere else—can you spell “land bridge”?

Welcome to the New World,
circa 1900
            The Kaufmans assert that “native” does not always mean “better,” nor can we assume that exotics always cause “harm” in “native” environments. This issue is about as far from cut-and-dried as you can get. Nonetheless, in our crisis-of-the-day national mentality, it’s just a hop, skip and a jump for some people to move from neutral non-native to frightening invasive.

Invasives poster child,  kudzu
(Pueraria lobata)
            Remember those 50,000 plant species introduced to North America since the 1500s I mentioned a while back? Well, about 5000 of those have escaped cultivation and moved in with the 17,000 “native” species. How did these foreigners get into the wild? Birds and rodents relocate lots of pre-fertilized seeds. Water and wind do their bits, carrying seeds and even entire plants over long distances. Large mammals join the party by transporting seeds and bits of roots on their fur or pants or shoes. Most new arrivals have proven to be good neighbors, behaving well and blending in nicely. On occasion, however, some thug will throw its weight around. The buzzword “invasive” applies to these rogues, the cause of all sorts wailing and gnashing of teeth among environmental purists and legislators.

The best definition of an invasive is “a plant that is too successful.” Its trademark trait is the speed with which it takes over an area. Examples of When Plants Go Bad in the South include kudzu, Asian wisterias, Japanese honeysuckle and Chinese ligustrum (a.k.a. privet). New York battles purple loosestrife and milfoil. In the Middle Atlantic states and the Northeast, burning bush, barberries, and Miscanthus cause problems. South Florida fears nandina, melaleuca, and many, many others. The Irish suffer from troublesome volunteer butterfly bushes growing in their gutters and chimney pots. And so on.

The Invasives Alert page from
June 2011's Fine Gardening
            “Invasives” appear globally, but are they necessarily a problem? Some scientists theorize that more than 90 percent of all species that ever lived on earth have gone extinct. (How did they determine that? I don’t know.) Must we assume that “change” equals “harm”? We cannot turn back the clock to the time of North America’s virginity. Isn’t it possible that what we perceive as “invasiveness”—or “man-made global warming”—is really part of an on-going process, and that maybe everything, even Homo sapiens, only gets to stay on the stage temporarily?

             There’s also the local character of invasiveness to factor in: for example, kudzu’s not a problem in Minnesota.
Anyway, the challenge facing both the horticulture industry and gardeners boils down to avoiding being part of the problem. Most states’ Cooperative Extensions post lists of local potential invasives on the internet, as do watchdogs like the Nature Conservancy, the Invasive Plant Atlas, the USDA Plants Database, the National Invasive Species Information Center, and Invasive Alert. Connecticut leads the way in outlawing flora non grata, legislating against anything that’s invasive anywhere. (In fact, I’m considering relocating there, as they must have already handled the important stuff like universal health care, unemployment, education, immigration problems, and the shrinking of the middle class. You think?) If you suffer from technophobia, as I do, call your Extension or State Department of Agriculture: they will sigh heavily and eventually mail you something. The Kaufmans’ book has a long list of sources of information as well.

Looking for alter-"natives"?
            Some people think the only way to combat invasiveness is to use only natives, and write hefty tomes on the subject (like Armitage’s Native Plants for North American Gardens and Native Alternatives to Invasive Plants—see Good Reads at right). Seems to me a lot like throwing out the baby with the bath-water, however. Your real-life options? Refuse to use plants like Japanese honeysuckle and barberries, boycotting the nurseries and garden centers that grow and sell them; or keep a tight rein on your beloved specimens, including provisions in your will that potential invaders be immolated with you on your pyre.

Check out these books by 
Allan Armitage
or C. Colston Burrell
             A parting thought: in the August-September 2007 issue of Horticulture, Carol Reese responds to a reader letter about her recommendation of a plant considered to be an invasive in some places by saying, “My main concern is loss of habitat, and humans are the worst of the invaders… [E]cologically sensitive landscapes… need not be all native, especially if the plants are those that can be grown without chemicals… The Earth is in a constant state of flux, which does not relieve us of responsibility, but requires us to make the best choices we can with what information we can gather.”
            So get informed before you plant. And whatever else happens, don’t you be slipping in a cutting of kudzu to cover your new pergola. Unless you live in North Dakota.


P.S.—You may want to invade Plant Delights Nursery’s Fall Open House. It's being held the weekends of September 9-11 and 16-18. Weather’s nicer now, if you weren’t up to facing the summer do.