Category Archives: Invasives

“Invasive” Plants Invaluable to Degraded Environment


© Marlene A. Condon
June, 2015

A large stand of Garlic Mustard (Alliaria petiolata), which is considered an invasive plant species, grows underneath a native Eastern Redcedar (Juniperous virginiana). Both kinds of plants, located along a gas pipeline, tell the informed observer that the soil in this location is nutrient-poor and compacted. (Photo credit: Marlene A. Condon)
A large stand of Garlic Mustard (Alliaria petiolata), which is considered an invasive plant species, grows underneath a native Eastern Redcedar (Juniperous virginiana). Both kinds of plants, located along a gas pipeline, tell the informed observer that the soil in this location is nutrient-poor and compacted. (Photo credit: Marlene A. Condon)

As April transitioned into May, I was surprised to see a fair number of daffodils still blooming along the roadway where I walk. It was a sign of how chilly the spring had been.

Another sign I picked up on that morning was the “invasiveness” of daffodils. There were many, many daffodil clumps spanning the miles of my exercise route. They exemplified the ability of some plants brought to this country to reproduce successfully enough to move well beyond the garden gate and out into the larger world.

Such so-called invasive plants have constituted an issue for some time now, although I don’t recall ever hearing anyone complain about the invasive nature of daffodils. Perhaps if a plant is lovely, people can forgive its tendency to reproduce and spread.

But when you are talking about the health of our environment, you can’t entertain such biases. If a plant meets the criteria for being considered “bad,” then it shouldn’t be granted a special exemption.

This situation begs the question, “Should nonnative plants be considered pestiferous when they spread?” I say absolutely not in most cases, especially in back yards, along hiking trails, in meadows and fields, and by roadsides. These plants are providing an invaluable service to a degraded environment.

Usually nonnative plants fill an area only after it had been left barren because of an altered soil profile brought about by man, severe storms, or both. Very few native plant species can grow in poor-quality soil.

By moving into these damaged areas, alien plants do what humans can’t easily do: they rehabilitate the soil. In other words, they are creating a rich soil so that—once they’ve done their job—native plants may again be able to grow there.

Nonnative species are able to obtain nutrients from nutrient-poor soil and transform them into plant tissue. When that plant tissue is returned to the soil (such as when leaves detach to be replaced by new ones or when the plant itself dies), it becomes humus—organic material that enriches the clay soil because its nutrients are in a form that’s usable by many more kinds of plants.

But enriching the soil is not the only thing invasive plants are doing for the environment. They are also supporting our wildlife, all of which require plants for food, shelter, and nesting sites. Every plant on invasive-species lists provides one or more of these basic necessities to our critters.

Although “invasive” plants are often referred to as noxious (deadly, harmful, dangerous), they are simply doing what they are meant to do—reproduce and multiply if there is room for them and the growing conditions are right. It’s what “happy” plants do.

Consider Japanese Knotweed (Fallopia japonica), a large herbaceous perennial plant that was brought from Asia to this country in the late 1800s. Its flowers feed abundant numbers of insects, especially bees of many kinds.

Yet according to the National Invasive Species Information Center, this plant is problematic because “it crowds out native species.” Well, yes, Japanese Knotweed eventually gets large enough and spreads enough to take up space so nothing else can share the space, but in all likelihood, this plant is not crowding out native species, but rather, other nonnative plants like itself!

One of the reasons this plant was originally brought to this country was erosion control after the ground had been denuded by man’s activities, such as road building. The only reason to bring in a foreign plant to prevent soil from washing away in these areas during rain storms is because no native plant could possibly handle the job.

During construction, heavy equipment clears away topsoil that native plants have evolved to grow in. The subsoil that remains is hard, and made harder still by the heavy equipment driven over it. It takes a tough plant to grow in heavy, hard-as-rock dirt!

In Charlottesville, the City Council recently voted to continue to use pesticides for controlling unwanted plant growth, such as Japanese Knotweed growing along the Rivanna River. People believe the plant “will take over next to streams so nothing else can grow there,” creating “a monoculture.”

However, it could well be that nothing else can grow there. The Rivanna runs red every time there’s a heavy rain. That color signifies sub-soil erosion, the result of development upstream and properties on which land has been cleared right to the edges of streams (it’s allowed on “pasture” in Albemarle County).

Although that soil is traveling towards the Chesapeake Bay and is a major contributor to its impaired state, some of it gets deposited along the edges of the waterways. This red clay is not typically conducive to native-plant growth, which is why nonnative plants were able to start growing in the first place and to subsequently “take over.”

Although one might think the land along the river is in a pristine state, it’s easy to discern the truth of the matter by simply examining what plants are growing with the Japanese Knotweed. If you see many so-called invasive species, such as Japanese Honeysuckle (Lonicera japonica), Garlic Mustard (Alliaria petiolata), Japanese Stiltgrass (Microstegium vimineum), and Autumn Olive (Eleagnus umbellata), that’s an undeniable sign of disturbance.

Killing and then replacing the Japanese Knotweed plants along the Rivanna River will simply re-disturb the soil, setting back the clock for its rehabilitation. If people truly want to help the environment, they need to take the long view.

Over time, the Japanese Knotweed will ultimately be shaded out by trees because Mother Nature’s goal is to create forest. No environment is static; it’s constantly in a state of flux.

People can spend time, effort, and money to remove nonnative species that are able to grow vigorously in disturbed areas of our making, but it’s virtually impossible to do so without re-creating the conditions that brought about the problem originally.

In the majority of situations, it’s difficult to make right what man has done wrong. Better to take the passive approach and let Mother Nature perform the renovations.

In fact, the whole invasive-plant issue has been a huge disaster for our environment. As a result of the rush to judgment that says all of these plants are “bad,” no matter what, herbicide usage has increased tremendously. Even most environmentalists now consider the employment of pesticides acceptable.

It’s as if poisoning the Earth is far better than allowing plants to exist in areas where they are not native. Rachel Carson’s ashes must be whirling in her grave.

This scientist, by recognizing the dangers of pesticides, brought about the environmental movement in which people began to recognize the effects of their actions upon the planet.

Yet now these poisons (substances that are capable of causing illness or the death of a living organism when introduced or absorbed into its system) are seen as either totally innocuous or a choice that is preferable to the alternative.

What is the alternative? The alternative is that a nonnative plant should occupy a spot of ground that in most cases is degraded and incapable of supporting a native plant anyway.

Herbicides sicken and kill many kinds of organisms, either directly or indirectly. Alien plants, on the other hand, often do far more good than harm to the environment. Can there really be any doubt about which choice is the better one to make?

Non-native Plants Can Be Remarkably Nature-friendly, Part One


© Marlene A. Condon
July, 2015

When home construction destroys the soil profile, it’s difficult for native plants to take root. (Photo credit: Marlene A. Condon)
When home construction destroys the soil profile, it’s difficult for native plants to take root. (Photo credit: Marlene A. Condon)

Many people have taken to heart the words of Doug Tallamy (the entomologist who wrote Bringing Nature Home) to grow native plants because many native leaf-eating insects depend upon them.

They’ve also been moved by his statement that “aggressive plant species from other continents…were rapidly replacing what native plants” were on the rural property he and his wife had purchased. Now people consider it a truism that non-native plants simply move into an area and push out native species.

But Mr. Tallamy’s presumption was made without consideration of the prior history of his newly acquired parcel. The Tallamys had purchased land that “had been farmed for centuries before being sold and subdivided.” What had actually happened was that alien plants colonized barren, abandoned, nutrient-poor farmland with a disturbed soil profile—something I’ve watched happen in Virginia since I was a college student in the 1970s.

At that time, the Eastern Redcedar (Juniperous virginiana) was the bane of many a cow farmer because these native trees constantly tried to move into their fields of compacted soil bereft of organic matter (other than cow pies) for who knows how long. This phenomenon was, and still is, something that can be observed, especially along I-81. Over the years, I’ve gotten off the highway numerous times to document it in photos.

By the 1980s, cow fields along I-81 were beginning to be abandoned. I noticed how they filled eventually—I’m talking years—with either redcedars or non-native Autumn Olive shrubs (Eleagnus umbellata), or a mix of both. Doug Tallamy’s land had likewise taken years to become “at least 35%” non-native vegetation because he mentions removing Oriental Bittersweet (Celastrus orbiculatus)—vines considered invasive—that had 6-inch-caliper trunks. That size isn’t reached overnight.

Therefore by the time he started to remove non-native plants, they’d had time to accomplish some degree of soil rehab, which is why some native trees could grow at that point. He can be forgiven his misperception because, unless you’ve been paying attention for decades, as I have, you won’t have a clue about this process.

The fact is that most yards are rather similar to cow fields, except that their soil profile has been totally rearranged by land clearing and grading. This was, in fact, the situation when I moved into my house almost 30 years ago.

The cleared and re-graded land had exposed gray clay subsoil in most of the yard. As someone who’d been enthralled by astronomy since the age of seven, I couldn’t help thinking my back yard looked like the surface of the Moon! The rest of the yard consisted of the more-typical Virginia red clay.

Obviously there was no way that I could personally improve such a large amount of soil for the sake of native plants. It would take years of rehabilitation, mostly executed by non-native plants that didn’t mind one bit growing in a disturbed soil profile.

Thanks to alien plants, my moonscape very quickly became a nature-friendly garden that supported an incredible diversity and abundance of wildlife—even more so than had existed here when the land was deeply shaded by forest.

I’d spent time on the property throughout the seasons to document wildlife usage before a small area was cleared where my house was to be built. I discovered that it’s a myth that mature forest is the pinnacle of wildlife abundance.

The reality is that it supports nowhere near the amount of life that a field (or meadow) habitat is capable of supporting—and a field habitat is exactly what most yards can be easily transformed into! Although you may immediately think “ugly” when envisoning a field, you shouldn’t.

When I talk about creating field habitat around your house, I’m referring to the incorporation of the qualities of a field: an open area with a large variety and number of herbaceous plants, surrounded by shrubs and trees to create edge.

I am not implying that your yard must be totally wild and unkempt, although the more natural it is, the better it will provide for life. Rest assured, a nature-friendly garden can be very nice looking.

Even though many species of native plants have naturally moved into my yard over the decades as the soil has improved, I would never completely remove the alien plants I deliberately brought into the yard many years ago. They are so beneficial to wildlife that, in fact, they have sometimes been life-saving.

Several years ago, deer consumed most of the native herbaceous plants in my yard and took most of the leaves off small native shrubs and trees. As a result, the denuded woody plants were unable to produce fruits. To add insult to injury, the following winter was very cold and snowy, which meant fruit-eating birds were in desperate straits.

But luckily for a flock of bluebirds that visited my yard that winter, my Japanese Barberries (Berberis thunbergii)—shrubs that deer do not normally feed upon—held numerous small red berries which the birds consumed over the course of a few days.

Japanese Barberry can spread and is thus considered invasive, yet it can’t be denied that those bluebirds—a species that is not commonly seen in my yard—were aided by it. They were obviously on the move, desperately seeking food which they found on my deer-ravaged property where only some kinds of alien plants had been left alone by the hoofed browsers.

Indeed, the many years of overpopulated deer herds have played a significant role in the enablement of so-called invasive plants. By keeping areas cleared of native plants, deer created opportunities for alien plants to move in. In actuality, the invasive-plant situation cannot be dealt with realistically until deer numbers are truly kept in balance with the environment.

I’ve seen far more wildlife—both in species and in numbers—in my yard over the past three decades than most folks will ever see in a lifetime of visiting wildlife refuges and national parks. As a result, I know that non-native plants are not only beneficial to wildlife, but also to soil rehabilitation that allows native plants to show up when conditions are suitable for their survival.

There are certainly situations in which alien plants shouldn’t be introduced, but most yards don’t fall into that category. In a world overrun by humans, with wildlife struggling to survive on our terms, it’s foolish to suggest that non-native plants should be removed (usually by using herbicides) on private property that is in no condition to support native plants.

It’s a myth that non-native plants do not provide adequate food, shelter, and nesting sites for many kinds of wildlife; in fact, many non-native plants are remarkably nature-friendly.

In part two of this article, I’ll discuss five woody non-native plants in my yard that have been the most valuable to the critters in my area. I’m sure you’ll be surprised.

Blue Ridge Naturalist: Non-native Plants Can Be Remarkably Nature-friendly, Part One

Non-native Plants Can Be Remarkably Nature-friendly, Part Two

© Marlene A. Condon
August, 2015

Despite what horticultural lore says, Yellow-bellied Sapsuckers do no lasting harm to healthy trees and shrubs when they make their shallow wells to obtain sap. (Photo credit: Marlene A. Condon)
Despite what horticultural lore says, Yellow-bellied Sapsuckers do no lasting harm to healthy trees and shrubs when they make their shallow wells to obtain sap. (Photo credit: Marlene A. Condon)

Not all non-native plants are created equal, nor are all yards suitable for their introduction. If you live near a natural area that is composed primarily of native plants, or if you live near wetlands, then you certainly should try to avoid growing alien plants that might spread into these relatively un-degraded areas.

However, if you want to start helping wildlife even though your yard consists mostly of subsoil, which is not very conducive to the growth of native plants, there are numerous alien plants that are already part-and-parcel of our environment that are wonderfully nature-friendly. I’ll start with three non-native woody plants I originally chose for their red foliage—my favorite color.

When I planted Chinese Photinia (Photinia serrulata), I had no idea how valuable this multi-stemmed shrub would be to wildlife and my wildlife viewing. In winter, Dark-eyed Juncos and White-throated Sparrows sleep among the branches, being replaced by Northern Cardinals and Eastern Phoebes in spring. I’ve even had an Eastern Screech Owl perch in there while waiting for darkness to descend on late-winter and very early-spring days.

What I’ve found most interesting, however, is the heavy use of these plants by Yellow-bellied Sapsuckers. Birds of the north that migrate to Virginia for the winter, these woodpeckers use their beaks to drill small holes (“wells”) into the bark of trees from which sap oozes. This sweet liquid provides them with carbohydrates, a source of quick energy.

Sapsuckers have visited my photinias regularly throughout the decades and it’s obvious. An inspection of the trunks reveals rows and rows of old and new sap wells, an undeniable sign of the affinity these birds possess for photinia sap. But they aren’t the only ones that want a sweet drink! Tufted Titmice, Carolina Chickadees, Downy Woodpeckers, flying insects (on warmish winter days), and even Gray Squirrels visit the wells.

And as if this wildlife usage wasn’t enough, the small white spring flowers attract so many bees that you can hear the loud buzzing well before you are within sight of the plants, and the resulting red fruits feed birds and mammals come fall.

My plants are almost 30 years old but have never produced a seedling, so Chinese Photinia is not likely to spread of its own accord. I should warn you that the flowers don’t smell very good, but because the blooming time is rather short, it’s not something you have to put up with for a long time.

Lastly, to take advantage of all of the benefits these plants offer to wildlife, they should be allowed to grow into their natural shape and height (up to 30 feet tall), rather than grown as a constantly sheared hedge, as is so often done. Photinia hedges are almost invariably doomed to leaf spot (caused by a fungus) because the pruning causes a thick growth of leaves that can’t get good air circulation to dry them.

It should also be noted that pruning is injurious and really shouldn’t be done unless it’s absolutely necessary. Woody plants can handle a bit of pruning because they’ve evolved with animals that feed upon them, which of course, prunes them. But too much feeding by animals or pruning by people can kill plants.

I love the red leaves of Japanese Maple (Acer palmatum), but I also love its value to wildlife, which came as quite a surprise and delight!

When the trees’ buds start to swell, they are ready to be eaten by Gray Squirrels and White-throated Sparrows that visit often. The buds they miss develop into blooms that bring the insects swarming: flies, wasps, a multitude of tiny bees, and butterflies, such as the Spring Azure and Tiger Swallowtail. The resulting seeds are eaten by Gray Squirrels.

Japanese Maples are very slow-growing trees, so you’ll be resigned to enjoying only their beauty until their wildlife potential develops.

I first became familiar with Burning Bush (Euonymus alatus) when I was a college student at Virginia Tech. A yard I walked by on my way to town had a huge specimen that was spectacular in the fall when its leaves turned a bright red. I knew I had to have one of these plants some day when I was permanently settled somewhere!

Although bashed as an invasive plant, Burning Bush is useful to many kinds of animals. The little yellow spring blooms attract a variety of tiny insects, especially bees. Small winged fruits develop that feed Northern Cardinals and White-throated Sparrows as well as Gray Squirrels. And in late winter, Dark-eyed Juncos and White-throated Sparrows visit daily to feed on the enlarging buds.

I’ve observed White-tailed Deer eating the leaves of Burning Bush. However, they only began to feed on this plant in the past few years as deer numbers were exploding in Virginia, suggesting it’s not a preferred food plant for them.

Burning Bush is originally from Asia and can indeed spread. But my own yard is so full of plants that most so-called invasive plants struggle to stay put, never mind increase in number (the reason I know experientially that these plants need a cleared area before they can start growing somewhere). If Burning Bush could be troublesome in your area, you probably shouldn’t grow one in your yard.

The Summer 2012 issue of the Butterfly Gardener was devoted to “The Great Butterfly Bush Debate” in which two butterfly gardeners took opposing stands on whether or not people should grow Buddleia davidii. This shrub, which has been widely planted as a nectar source for butterflies, is yet another plant from Asia that has spread beyond the gardener’s gate by way of seed production.

I have a Butterfly Bush that certainly does bring in butterflies. It does make seeds, but I’ve yet to find a seedling in my yard. Where I have seen this plant as an escapee from the home garden is along miles and miles of train tracks, which isn’t surprising. Just like other plants that are referred to as invasive, Butterfly Bush can tolerate the wretched growing conditions provided courtesy of the railroad companies.

Luckily, you don’t need to grow Butterfly Bush. If you want a shrub attractive to butterflies (and bees), I highly recommend Glossy Abelia (Abelia x grandiflora) as a substitute. Developed from plants native to Asia and Mexico, this hybrid does not make seeds and thus does not move out of the area. It blooms from spring until frost, making it the perfect substitute for Butterfly Bush if your yard has poor soil.

Shrubs and small trees, unlike flower beds, do not take much effort to maintain. If you want to help wildlife without a lot of fuss and bother, by all means grow woody plants such as the ones I’ve mentioned here (with the exception, perhaps, of Burning Bush).

But to bring in the highest number of wildlife species, you require flower beds that contain a diverse array of plants in abundance, whether they are native or naturalized (which is really what “invasive” means). The easiest way to find out what will grow best in your soil is to clear a bed for plants and see what comes up. Those are the plants best suited to your growing situation and that will provide for wildlife.

Blue Ridge Naturalist: Non-native Plants Can Be Remarkably Nature-friendly, Part Two

Native plants aren’t always better

“Native plants aren’t always better”, published 04/21/2008, The Roanoke Times

Editorial commentary

Marlene A. Condon

Condon is the author of “The Nature-Friendly Garden” and is a Virginia naturalist.

A war is being waged against aliens. Your children are probably being trained and enlisted to fight the battles. Even your local power company may be getting its employees to volunteer in the effort to root out aliens.
Illegal immigrants? No. Non-native plants are the aliens sought out and destroyed.
Yet without these aliens in our midst, our wildlife will find it harder to find food and our soils will not be rehabilitated for the benefit of native plants.
When early European colonists arrived in North America, they found an ancient landscape of huge trees growing on nutrient-dense, dark soil composed of humus. Much decomposition had occurred throughout the eons to produce the rich soil required by the plants growing beneath the leaf canopy.
When settlers cleared the land, they opened the canopy and planted crops that immediately began to deplete the aged soils of their nutrients. Many of the flower seeds brought, intentionally or unintentionally, by the human immigrants became naturalized citizens of their new environment.
Over time, these new plants spread, moving into the clearings where native plants were no longer able to grow because conditions had been altered.
And throughout the next 400 years, people continued to change the landscape as well as bring in new plants that could take advantage of disturbed areas created by man — and sometimes by nature.
Now such plants are considered invasive and are much maligned. But do they truly invade and destroy habitat for wildlife? This perception is unequivocally wrong.
Physics tells us that no two objects can simultaneously occupy the same space. Alien plants verify this by moving only into areas where open space is available for them to grow. After a few decades have passed without native-plant competition, they may fill the area.
So-called invasive, non-native plants are survivors and rehabilitators that can withstand poor-quality habitat (such as highway medians), polluted areas (dredge spoil, sewage sludges and mining tailings, for example) and the well-trodden soil of hiking trails (in national parks and forests).
Indeed, alien species grow successfully in our yards because subsoil has been exposed or topsoil compacted. They also do well in wetlands with soil profiles that have been disturbed by man or weather.
It’s simply not true that many non-native plants are invaders that take over important habitat for wildlife. These plants move into degraded areas that are devoid of good-quality soil upon which most of our native-plant species depend, and we should leave them to do their work.
To try to replace aliens too soon with native plants is misguided; it serves only to impede the necessary rehabilitative process. Once rehabilitation is accomplished, our native plants will move back into these areas.
Man, however, may wish to hasten the process along by removing the non-native species instead of letting them die out naturally. But this task should be done only after the really hard work of transforming the soil so that it is usable by native plants has been completed, free of human effort and expense.
Tax dollars should not be wasted on highway medians in an effort to replace, for example, common mullein with fescue grass that is just as non-native, or purple loosestrife with common cattail that can just as quickly create a monoculture.
Additionally, it’s questionable whether public funds should be spent on the removal of non-native plant species from wetlands with environmental issues, such as degraded water quality.
All of this is not to say that people should deliberately plant non-native species. It is extremely important to maintain our native diversity of insects, many of which are dependent upon a very limited selection of plants to survive. Thus, folks should incorporate native plants into their landscapes as much as possible.
But it’s foolish to root out alien plants that can and do provide habitat for numerous mammal, bird, insect, arachnid, amphibian and reptile species. That’s something bare ground cannot do.