Japanese Knotweed

January, commuting to work, pittsburgh

Back in Pittsburgh, in January a new semester begins, which we optimistically call "spring semester." Spring semester, however, ends just around the time spring weather begins to be reliable, in late April. But at the start of that semester, biking season is decidedly over for me, and even driving to work is a journey best undertaken with good tires and a bit of extra time.

When driving, I dislike the snow, but in general, I prefer snowy winter days strongly over the brown, drab, cold alternative. Snow makes the hillsides look clean and fresh, whereas melted snow shows all the flaws: the trash tumbled down the worst hillsides, the bare mud on others. Many weeds become nearly unrecognizable in this season, with their leaves gone and their seeds mostly dispersed. Japanese knotweed, however, remains particularly distinctive, with its arching, person-high, reddish brown stems, each leaf node bent slightly from the one below, resulting in a shape a bit like a bent, oversized bobby pin. In the annals of erosion control, Japanese knotweed (Polygonum cuspidatum) has to be one of the most dramatic success stories that everyone regretted. Japanese knotweed was brought as a garden plant, partly for its spray of white, bee-friendly flowers (Japanese knotweed honey is quite dark and rich), but mostly for its potential to control erosion on bare hillsides. Certainly, Japanese knotweed has spread across many hillsides, and in three seasons this plant protects ground with its large, spade-shaped leaves. But I'm not convinced that it really protects soil during the January thaw and the wet weather of early spring, when rain replaces snow and the ground dissolves in mud. And worse, Japanese knotweed seems to make growth of anything else impossible—even chickweed has no time or light to sprout during that brief season of leafless knotweed. Native plants simply don't have a chance against this spreading giant, and yet all winter the knotweed offers only bare stalks, towering above the vacant soil.

Japanese knotweed is not to be confused with its native weedy cousins. I recently saw a bowl advertised in a catalog with Pennsylvania smartweed or lady's thumb painted decoratively on its side (I couldn't tell which one from the picture; a few hairs on the leaf base distinguish one from the other). These two species are a bit lanky, but bear clusters of deep pink, tiny round blooms on their stalks. The knotweeds and smartweeds are in the same family as buckwheat, which is, as far as I know, the only crop in the family. Japanese knotweed is, according to Euell Gibbons, an acceptable substitute for asparagus in early spring, but I don't trust that recipe the way I trust the one for dandelion wine. There's something insidious about Japanese knotweed, and I'm not sure I like the idea of letting it past my lips. If it is true that "you are what you eat," I know I don't want to be knotweed. While next year's Japanese knotweed and asparagus both are still dormant underground, the ground is churning with the freeze-thaw cycles of a temperate-zone winter. This season is when erosion becomes most obvious. We think of late fall and early spring as "mud season," and the term is apt. But what impresses me most about weeds and erosion is (1) weeds are very good at cheap erosion control, and (2) we wouldn't have ever needed to introduce weeds for erosion control if we had used some common sense about plants and ground cover. Particularly as we move toward thinking of new species of plants as potential "biofuel," I would suggest a fresh look at our more dramatic weed-introduction mistakes of the past. Japanese knotweed is far from our first introduced weed nightmare. In the United States, kudzu, a viney cousin of clover, also from Japan, was one of the first species introduced and regret ted. Like knotweed, it was introduced for erosion control, and kudzu certainly does that job well. It also controls power lines, privies, sheds, and houses whenever they suffer from loneliness or neglect in the Southeast. I don't know if kudzu was originally introduced with freshly built roadsides in mind, but it certainly thrives there now. Some studies suggest that kudzu may be a plant that thrives even more in the high carbon dioxide environment we create with the fuel of our daily commutes.

Another species that is currently used for erosion control on abused land is Chinese lespedeza, a bushy cousin of clover, with fingernail-sized oval leaves and inconspicuous yellow or white flowers. This is a plant commonly chosen by coal companies as part of their "reclamation" efforts, a legume that tolerates abused soil very well. However, unlike so many other legumes, this species is useless for wildlife—even deer—and so although it is green and photosynthe-sizing, preventing erosion, and helping the coal company by letting it leave the scene of the crime quickly, it isn't in any way helping the land become part of the ecosystem it once was. I don't know that it spreads invasively, and it can't be called a weed if people planted it, but if a weed were defined differently, Chinese lespedeza would fit the definition perfectly.

In A Guide to the Wildflowers and Ferns of Kentucky, biologists Mary Wharton and Roger Barbour describe a weed this way:

A "weed" produces a large quantity of seeds which have an efficient means of dispersal and a high percentage of germination, or is able to propagate itself vegetatively. Also it establishes itself readily in open situations and grows rapidly and profusely, with the result that it successfully competes with and crowds out more desirable plants. A weed has been incorrectly called "a plant out of place," but it is not a weed unless it has the capacity for "taking over the place."

I've chosen not to take their definition for lawn weeds because I think the "plant out of place" definition is more commonly how keepers of perfect lawns view them—whether it spreads or not, no plant besides grass will be tolerated. However, this ecological definition points to the problems with plants such as lespedeza, Japanese knotweed, or kudzu.

Many gardeners and wildlife enthusiasts celebrate the benefits of native plants, both by selecting them for their gardens and by rooting out introduced species. I have heard Newcomb's Wildflower Guide—arguably the best guide in current use for amateur flower identification—criticized for the fact that it makes no distinction between native and introduced, and I have wished at times that this information were included in it. Sometimes, though, I don't see the point in distinguishing—once the plant is established, we can't ship it back. When I'm identifying a plant, I don't need a separate guide for native versus introduced plants. Plus, frankly, not all introduced species are evil. I have a great deal of respect for native plants, and I'm more likely to give them the benefit of the doubt, but I'm not a purist.

We can't eliminate the introduced species, anyway. Even weed scientists, people whose livelihoods involve finding ways to kill or prevent plant growth, typically talk not about eradication but about "control." Eradicating a plant entirely is something we're excellent at only with the help of habitat destruction, as in the nineteenth century when we plowed the prairies to almost nothing and many of those native species went extinct. Weeds, as Wharton and Barbour point out, excel at taking advantage of any open spot and are not so picky as their native cousins are about destroyed habitat.

The fact that weeds take advantage of any open spot is something we might even value about them, if we thought about it more. Most of us don't find bare soil all that appealing, and certainly we all know that bare soil means dust and mud, which can lead to Dust Bowls and mudslides. We think nothing of disturbing soil for human development: houses, malls, and roads all begin with removing the natural ground cover. The Little House on the Prairie series is all about the way Pa Ingalls cuts trees and plows prairie to make way for the crops he continually fails to grow well enough. Weeds are never blamed for his problems, but we can be sure that each of his failed fields was thriving in weeds within a year after he moved further west. Pa Ingalls plowed the ground and cut the trees for crops, but in the wake of the covered wagon, he opened the soil up for weeds.

Weedy pioneer plants, like Pa Ingalls's, don't establish themselves in areas where native populations are thriving and healthy. Instead, pioneer plants take advantage of land left open when the natives have been plowed, torched, or poisoned. Yes, that means that European settlers were just like weeds, traveling west in the path left by Custer, alcohol, and smallpox, while the weeds both followed us and sometimes even led the way. Kentucky bluegrass was an introduction from Eurasia but arrived in Kentucky ahead of white settlers, giving the appearance of being local, when in reality it was just scouting out territory for the Europeans who brought it on their boats.

Some weeds, like purple loosestrife (Lythrum salicaria), a lovely purple spike of flowers on a network of perennial stems, can spread seemingly without previous damage to existing plant communities. I've seen purple loosestrife in wetlands throughout rural New York, in places without a house or barn in sight. Yes, wetlands have been destroyed by development in many areas, but purple loosestrife— a plant introduced as a garden ornamental — has invaded wetlands even in areas we haven't bothered in decades, if ever. What gives purple loosestrife and many other invasive weeds their advantage is that they lack natural controls. For example, a number of beetles are known to consume and control purple loosestrife in its original homeland, and these beetles were left behind when the first exotic-plant gardeners brought loosestrife to the States. Some of these insects have been introduced to control purple loosestrife here, with some local success. These insects don't seem to spread, but they do help wetlands where schoolchildren and ecologists introduce them. Although the problem with purple loosestrife is far from solved, many other invasive weeds remain here without any taunting from the pests who controlled them back at home. Japanese knotweed is among these uncontrolled invaders.

Japanese knotweed is a threat to natural areas. The Western Pennsylvania Conservancy controls it with a double herbicide application, because no single one works. The Pittsburgh Parks Con servancy doesn't employ herbicides, but it has tried to control the plant with thick black plastic mulch, which has to be left in place for perhaps three years to ensure certain death. Japanese knotweed reproduces prolifically, but like many invasive weeds, it also spreads underground. And it's perennial, so preventing seed set wouldn't be half enough to get rid of it.

I have seen Japanese knotweed in many other states across the country. The first time was in a dark, wet, spring-fed gorge in Ithaca; the woodland was thick enough that I couldn't quite see what the problem was with this plant of ill repute. Japanese knotweed isn't terribly shade tolerant, and in that location it was not at its strongest, just a few gangly stalks spread through a little glen, with plenty of other plants interspersed. Around Pittsburgh, I see it along the rivers, along roadsides, along railroads, and thick in the edges of urban parks. I've seen it in abandoned urban gardens, where it isn't clear whether the gardeners left and the knotweed followed, or the knot-weed eradicated the gardening efforts.

I hiked through a thicket of Japanese knotweed on a hot day in June, something like eighteen miles from the western end of the Rachel Carson Trail. The thicket wasn't exactly roadside, despite the six hundred travelers on the trail that day, but it was in a power line right-of-way. I've seen it in similar areas near other power lines and trails. That particular day, I was so addled by heat and fatigue that I was actually grateful for its shade; the stand was easily over six feet tall. As in many stands of Japanese knotweed, not a single other seedling was growing in its shade. Japanese knotweed may not be shade tolerant, but it certainly seems to prevent even the most shade tolerant of other plants from spoiling its exclusive parties.

In the years before Japanese knotweed was introduced, we plowed the soils of New England for our small colonial farms, but two hundred and fifty years later we have lovely stands of sugar maples forgiving us for the abuse—or maybe those early small, diverse farms just didn't provide the same kind of soil abuse we give out now. Where we plowed the prairie throughout the Chicago region, the land, left alone, has grown into "forest preserves." These woodlands reward us with shade and recreational hiking—entirely unlike the prairies that preceded them, but lovely nonetheless for excursions from urban chaos. We have been spoiled by the many cases where we dug up the native plants and something else beautiful grew in their places. Sometimes we've even seen a comeback of the natives themselves.

We aren't always this lucky, and Japanese knotweed may be more what we deserve. Much of this book is about weeds I love, or love sometimes, and why I think we should tolerate them in our yards. This chapter is about a weed that tells us how wrong we are to think we can plow, develop, poison, and destroy soil on the assumption that the plants we want will just grow back anyway. In Pittsburgh, we treated the rivers for decades as toxic waste dumps and free roadways for the discarded fruits of our riverfront factories. How could we possibly expect something lovely and native to grow there, just because the steel mills are gone and the river is now only half as polluted? Japanese knotweed growing by the rivers is not what we want there, both because it doesn't leave room for those native plants we can't afford to cultivate lovingly enough, and because it spreads so readily, just at the moment our riverfront trails have started to attract residents eager to see the rivers as something more than a liquid conveyor belt for waste.

Though I don't think Japanese knotweed has much to say for itself, it is one of the plants that show us that our attitude toward development of land is deeply flawed. This flaw is never more obvious than in winter, when the bare stalks of this large, woody weed decorate the landscape where we might imagine snow, or even some other weedy ground cover, rather than mud. The ground in a thick Japanese knotweed stand is bare, brown mud, and it will stay that way, because nothing can germinate or survive in the density of that three-season shade. Japanese knotweed may have been introduced to prevent erosion, but this only works in winter if the seasonal ground cover is snow. I have never seen snow deep enough to hide a stand of Japanese knotweed in winter.

Weed introductions are often done in situations where we are in too much of a hurry to let the native weeds do their jobs well. Perhaps the native weeds' seeds are too small for our clumsy hands;

perhaps the plants are so spread out that it seems too much work to collect them. Perhaps the promise of some carpetbagger seed salesman is too tempting, and we believe that this time, the promised ground cover will just stay where we plant it and thrive there, without taking advantage of us. I'm sure the coal companies spreading Chinese lespedeza seeds in their wakes would argue that their solution is the most economical, and what's wrong with Chinese lespedeza anyway? Still, the history of coal mining leaves me no reason to trust that they would employ the best long-term solution for erosion control.

In the hindsight of winter, we can plan to do better next time. We know now that rooting out invasive weeds is backbreaking work, usually done on land with little or no economic market value. We know that the first species to volunteer in our bare dirt isn't even going to be Kentucky bluegrass, despite its trek ahead of the pioneers a few centuries ago. Our urban parks won't naturally fill up with our favorite shade trees and wildflowers, just because those plants might have been there before the first house was built. Japanese knotweed, among others, will lead the invasive parade.

In the worst way, we're alike, us and the Japanese knotweed. O pioneers!

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