Managing Spontaneous Urban Plants for Improved Aesthetics

As discussed last week, our wild, urban flora is a cosmopolitan mixture of plants that were either native to the area before it was developed, introduced from all corners of the world on purpose or by accident, or brought in by migrating wildlife. These are plants capable of establishing and sustaining themselves outside of human cultivation and management, and are found in abundance beyond the borders of our tidy gardens and manicured landscapes. They vegetate sectors of our city that have been abandoned, overlooked, or routinely neglected. Given enough time – and prolonged lack of intervention – such vegetation will proceed along the process of ecological succession in the same way that plant communities in natural areas do. And just like other plant communities within their respective ecosystems, these wild, urban plant communities provide a suite of ecological services vital to the health of our urban ecosystems.

Peter Del Tredici writes in Wild Urban Plants of the Northeast, “landscapes that include spontaneous vegetation fit the technical definition of sustainable in the sense that they are adapted to the site, require minimal maintenance, and are ecologically functional.” In an interview with Scenario Journal, Del Tredici goes on to define sustainability as “the value of the services provided by the ecosystem divided by the cost required to maintain that ecosystem.” Spontaneous urban landscapes offer “substantial ecological services at relatively low cost, or in some cases no cost,” and thus, by Del Tredici’s definition, they are “highly sustainable.”

There is one unfortunate downside – “weedy” landscapes like this are, by popular opinion, thoroughly unattractive and a sign of urban decay. This belief is held in spite of the fact that many of the plants found therein would be cherished or admired in other settings. Among deteriorating infrastructure, litter, and less attractive plants, some of our favorite plants are rendered guilty by association.

Despite their ecological benefits, abandoned areas vegetated with wild, urban plants are not favored by the public. So, to appease our aesthetic standards, sites like this can be enhanced through minimal intervention to be more attractive while retaining their ecological functions. In a paper published in a 2006 issue of Journal of Landscape Architecture, Norbert Kühn asserts that “to use spontaneous vegetation for ornamental purposes, a kind of enhancement or design work is necessary.” Species can be added and removed, and simple, infrequent maintenance measures can be implemented. Examples include extending the flowering season with spring flowering bulbs and mowing the area once or twice annually to maintain and improve the composition of the stand.

Wild bergamot (Monarda fistulosa) – one of the plants that Norbert Kühn included in his study as a candidate for improving the aesthetics of spontaneous, urban plant communities.

Favoring attractive weeds over less attractive ones and using minimal maintenance to improve aesthetics and function are the principles behind Del Tredici’s “cosmopolitan urban meadow.” In his book, he lists some criteria for plants that would be suitable for “this novel landscape form,” including: erosion control (long-lived; vegetatively spreading), stress tolerance (full sun; drought; compacted and polluted soil), aesthetic value (ornamental characteristics; not “weedy” looking), wildlife friendly (attractive to pollinators; edible seeds), and commercially available.

In an article in Harvard Design Magazine, Del Tredici and Michael Luegering describe the cosmopolitan urban meadow as “a stable assemblage of stress-tolerant, low-maintenance herbaceous perennial plants that are preadapted to harsh urban conditions and that will provide an attractive vegetation cover on vacant land.” Whether it is a “long-term landscape feature” or a placeholder until future development, it will have “the capacity to increase the aesthetic and ecological value of vacant land without the investment of large sums of money typically required for the installation and maintenance of traditional managed landscapes.”

Abandoned or undeveloped, urban lots like this one are ideal sites for “cosmopolitan urban meadows.”

In an urban context, some plant species are particularly noxious and may need to be removed from urban meadows, such as ragweed (Ambrosia spp.) for its allergens and poison ivy (Toxicodendron radicans) for its Urushiol-induced contact dermatitis. Species with a history of being invasive should also be avoided and contained, particularly in sites that are adjacent to or within a short distance from natural areas. Despite this and other minor concerns, spontaneous vegetation has great potential. In Kühn’s words it is “authentic” and a “reminder of the history of the site,” it is part of “the natural dynamic” with potential to bring us “closer to nature,” and finally, “it can be maintained for a long time [with] less care and low costs.”

Finding beauty in these urban, wild landscapes might even cause a shift in what we find appropriate for cultivated landscapes. In her book, Grow Curious, Gayla Trail reminds us that, despite all of our efforts, wildness persists even in our most earnest attempts to subdue it. Perhaps we should embrace it:

‘Wild’ and ‘cultivated’ are social constructs that we place in opposition to each other, when in reality there is a knotty labyrinth between them. We subjugate our cities and our gardens with chemicals and artifice because we are unable to see that wild and cultivated can be entwined, can be all at once tended, lyrical, surprising, domesticated, irrational, functional, and free.

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See Also: Arnold Arboretum’s Cosmopolitan Meadow at Weld Hill

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Is There a Place for Weeds in Urban Ecosystems?

Highly urbanized areas have a long history of disturbance. They are a far cry from the natural areas they once displaced, bearing little resemblance to what was there before. In this sense, they are a brand new thing. During the urbanization process, virtually everything is altered – temperatures, soils, wind patterns, hydrology, carbon dioxide levels, humidity, light availability, nutrients. Add to that a changing climate and increased levels of pollution, and the hope of ever seeing such a site return to its original state – whatever that might mean – is crushed.

What then should we consider the natural flora of an ecosystem like this? Certainly it is not the native flora that once stood on the site before it was developed; virtually none of the conditions are the same anymore. If we are defining “natural” as existing with minimal human intervention, then the natural urban flora would be whatever grows wild outside of our manicured landscapes and managed, remnant natural areas. It would be a cosmopolitan mixture of plants that have joined us in our migrations with and without our permission, along with a collection of species that are either extant to the site or have been brought in by wildlife. In many ways it would mirror the human populations of our modern cities – an assortment of residents from around the globe with diverse backgrounds and cultural histories.

In Wild Urban Plants of the Northeast, Peter Del Tredici classifies urban land into three general categories based on their ecological functions: native, remnant landscapes; managed, constructed landscapes; and ruderal, adaptive landscapes. Native, remnant landscapes are generally small areas within city limits that have never been developed. They contain a portion of the native plants that once populated the area, and they require vigilant and regular maintenance to keep non-native plants from invading and to control those that already have. Managed, constructed landscapes include all of the parks and gardens that have been designed and intentionally planted. They require regular maintenance of varying intensity in order to keep them looking the way they are intended to look. Ruderal, adaptive landscapes are abandoned or neglected sites that are populated by plants that have arrived on their own and that maintain themselves with virtually no human intervention. This is where the true, wild urban flora resides.

Prickly lettuce (Lactuca serriola) growing in an abandoned lot.

Many of the plants that make up our wild urban flora are what we commonly refer to as weeds. These weedy plants appear in landscapes throughout our cities, but are generally removed or controlled in all landscapes except the abandoned ones. It is in these neglected sites that weeds have the greatest potential to provide vital ecosystem services, performing ecological functions that are beneficial to urban life.

Not all plants are suited for this role. Spontaneous urban vegetation is particularly suited due to its ability to thrive in highly modified, urban environments without external management. Regardless of provenance, this suite of plants, as Del Tredici points out, seem to be “preadapted” to urban conditions and “are among the toughest on the planet.” A long list of traits has been identified for plants in this category, ranging from seed dispersal and viability to speed of growth and reproduction to tolerance of harsh conditions. Del Tredici summarizes by stating, “a successful urban plant needs to be flexible in all aspects of its life history from seed germination through flowering and fruiting, opportunistic in its ability to take advantage of locally abundant resources that may be available for only a short time, and tolerant of the stressful growing conditions caused by an abundance of pavement and a paucity of soil.”

Abandoned lots flush with weeds, overgrown roadsides and railways, and neglected alleyways colonized by enterprising plants are generally seen as ugly, unsightly eyesores – products of neglect and decline. Some of the plants found in such locations are valued in a garden setting or prized as part of the native landscape in a natural area, but growing wildly among trash and decaying urban infrastructure they, too, are refuse. As Richard Mabey has written: “If plants sprout through garbage they become a kind of litter themselves. Vegetable trash.”

Abandoned chicken coop overtaken by tree of heaven saplings (Ailanthus altissima).

Despite how we feel about these plants or the aesthetics of the locations they find themselves in, they are performing valuable services. Apart from adding to the biodiversity on the site as well as producing oxygen and sequestering carbon – services that virtually all plants offer – they may be preventing soil erosion, stabilizing waterways, absorbing excess nutrients, reducing the urban heat island effect, mitigating pollution, building soil, and/or providing food and habitat for urban wildlife. While cultivated and managed landscapes can achieve similar things, these neglected sites are doing so without resource or labor inputs. They are sustainable in the sense that their ability to provide these services is ongoing without reliance on outside maintenance.

Sites like these should be further investigated to determine the full extent of the services that they may or may not be offering, and in the event that they are doing more good than harm, they should be conserved and encouraged. One service that is receiving more attention, as Del Tredici writes, is phytoremediation – “the ability of some plants to clean up contaminated sites by selectively absorbing and storing high concentrations of heavy metals such as cadmium, lead, copper, zinc, chromium, and nickel in their tissues.” Weed species with this ability include prickly lettuce (Lactuca serriola), lambsquarters (Chenopodium album), and mugwort (Artemisia vulgaris). In an article in Places Journal, Del Tredici gives the example of the often despised, introduced plant, common reed (Phragmites australis) cleaning up the New Jersey Meadowlands by “absorbing abundant excess nitrogen and phosphorous throughout this highly contaminated site.”

In the book, Weeds: In Defense of Nature’s Most Unloved Plants, Richard Mabey writes: “As we survey our long love-hate relationship with [weeds], it may be revealing to ponder where weeds belong in the ecological scheme of things. They seem, even from the most cursory of looks, to have evolved to grow in unsettled earth and damaged landscapes, and that may be a less malign role than we give them credit for.” Perhaps, seeing them in this worthy role, will temper our knee-jerk inclination to demonize them at every turn.

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See Also: Our Urban Planet and Wild Urban Plants of Boise.

Summer of Weeds: Wild Urban Plants of Boise

The Summer of Weeds is a result of the curiosity and fascination I feel towards weeds. It is also inspired by Peter Del Tredici’s book, Wild Urban Plants of the Northeast, which encouraged me to take a closer look at the weeds that grow in my urban hometown of Boise, Idaho. Del Tredici’s book serves mainly as a field guide for identifying common weeds found in urban areas in the northeast region of the United States. Many of these weeds are found in cities across North America, so the guide is still useful regardless of where you live. Additionally, the book’s 25 page introduction is an excellent overview of how weeds fit in to the ecology of urban areas and an incentive to not only stop and get to know our urban flora but to respect it for its tenacity and durability and its important ecological role.

Excerpts from Wild Urban Plants of the Northeast by Peter Del Tredici:

From the Foreword by Steward T. A. Pickett –

If it is to fulfill its potential, the urban wild flora must be better understood and better used. In other words, its functions, not just its categories – native, exotic, invasive, naturalized – must be appreciated by professionals and citizens alike. Understanding should come before judgement when urban wild plants are concerned.

Defining urban wild plants –

The [plants] that fill the vacant spaces between our roads, our homes, and our businesses; take over neglected landscapes; and line the shores of streams, rivers, lakes, and oceans. Some of the plants are native to the region and were present before humans drastically altered the land; some were brought intentionally or unintentionally by people; and some arrived on their own, dispersed by wind, water, or wild animals. They grow and reproduce in the city without being planted or cared for. They are everywhere and yet they are invisible to most people. Given that cities are human creations and that the original vegetation that once grew there has long since disappeared, one could argue that spontaneous plants have become the de facto native vegetation of the city.

Why weeds are problematic in agricultural and horticultural settings, as well as in natural areas, is fairly intuitive. But why are they seen as a problem in urban areas, outside of our parks, yards, and gardens? –

When it comes to spontaneous urban plants, people’s complaints are usually aesthetic (the plants are perceived as ugly signs of blight and neglect) or security related (they shield illicit human activity or provide habitat for vermin). Indeed, the context in which a plant is growing not only determines the label that we put on it but also the positive or negative value that we assign to it.

Regarding urban ecology – 

[Cities] have their own distinctive ecology, dominated by the needs of people and driven by socioeconomic rather than biological factors. People welcome other organisms into cities to the extent that they contribute to making the environment a more attractive, more livable, or more profitable place to be; and they vilify as weeds those organisms that flourish without their approval or assistance. Regardless of humans’ preferences, an enormous variety of nonhuman life has managed to crowd into cities to form a cosmopolitan collection of organisms that is every bit as diverse as the human population itself.

To illustrate the point that urban weeds are playing a role in the ecology of our cities, Del Tredici lists the ecological functions of each species featured in the field guide portion of the book. These functions include:

  • temperature reduction
  • food and/or habitat for wildlife
  • erosion control on slopes and disturbed ground
  • stream and river bank stabilization
  • nutrient absorption (nitrogen, phosphorous, etc.) in wetlands
  • soil building on degraded land
  • tolerance of pollution or contaminated soil
  • disturbance-adapted colonizer of bare ground

Carbon storage and oxygen production are functions of these plants as well, as they are of all plants; however, as Del Tredici points out, “because [spontaneous urban plants] grow on marginal sites and require no maintenance, [they] are probably providing a greater return in terms of carbon sequestration than many intentionally cultivated species.”

There is much more to say about this “brave new ecology” and the role that urban wild plants play in it. Future posts are in the works. For now, consider this sentiment from Del Tredici’s book: Urban wild plants “are well adapted to the world we have created and, as such, are neither good nor bad – they are us.”

What follows are a few photos of some of the urban wild plants I have encountered in Boise over the last few weeks. These, along with the plants featured in previous Summer of Weeds posts, are a mere fraction of the species that grow wild in my urban hometown. The diversity of weeds alone in urban areas is astounding and should be given more consideration, along with the broader diversity of organisms that exist within our cities.

Creeping wood sorrel (Oxalis corniculata) along the driveway in front of my apartment

Prickly lettuce (Lactuca serriola) in an abandoned lot on Bannock Street

Yet to be identified thistle along 23rd Street

Field horsetail (Equisetum arvense) in front of post office on 13th Street

Pale smartweed (Polygonum lapathifolium) in a ditch at Idaho Botanical Garden

Tree of heaven seedling (Ailanthus altissima) in the backyard of my apartment

Birdsfoot trefoil (Lotus corniculatus) in the lawn at Esther Simplot Park

Weeds taking over a recently abandoned business on 27th Street

Creeping bellflower (Campanula rapunculoides) in the alleyway behind my apartment

Showy milkweed seedlings (Asclepias speciosa) next to horizontal juniper in a median on Parkcenter Boulevard

Purple loosestrife (Lythrum salicaria) on the bank of the Boise River near the Broadway Avenue bridge

Himalayan blackberry (Rubus armeniacus) along the Boise River Greenbelt near MK Nature Center

Summer of Weeds: Stinking Lovegrass

There are so many weedy grasses that we would be remiss if we let the Summer of Weeds go by without discussing at least one of them. As obnoxious and ecologically harmful as some of these grasses can be, they are easy to ignore, simply because they are not as showy and eye-catching as other weeds. They can also be difficult to identify, particularly when they are not flowering. To the untrained and unappreciative eye, all grasses appear alike and most are fairly uninteresting.

But some of them have great common names, like Eragrostis cilianensis, commonly known as stinking lovegrass, candygrass, or stinkgrass. This plant earns the name “stink” on account of the unpleasant odor that is released through tiny glands in its foilage and flower head. Probably due to my poor sense of smell, my nose doesn’t pick it up very well, but from what I can tell it has a funky or, as Sierra put it, “musky” smell. I imagine if you were to come across a large patch of stinking lovegrass blowing in the breeze, the smell would be detectable.

stinking lovegrass (Eragrostis cilianensis)

Eragrostis cilianensis is a short (up to two feet tall) annual grass from Eurasia and Africa. It is naturalized across much of North America. It has hollow and jointed stems with flat or folded leaves. Where the leaf blade wraps around the stem (an area called the ligule) there is a tuft of fine hairs. The inflorescence is highly branched, and the branches are lined with several compact, flat florets. The appearance of the flower head is highly variable, from tight and compact to spread out and open.

Inflorescences of stinking lovegrass (Eragrostis cilianensis)

Stinking lovegrass likes sandy or gravelly, dry soils in open, regularly disturbed areas with full sun. It is very drought tolerant and thrives in hot temperatures, which is why it is unfazed growing in the cracks of sidewalks and pavement. It can grow in rich, fertile soil as well, and so it often makes an appearance in vegetable gardens, agricultural fields, and ornamental garden beds.

Stinking lovegrass growing in a crack between the pavement and the sidewalk

There are dozens of species in the genus Eragrostis, with representatives around the world. A few are native to North America, and a few others have been introduced. Provenance aside, all have the potential to be weedy. Eragrostis curvula, weeping lovegrass, is an aggresive invader in some regions. Eragrostis minor, lesser lovegrass, is similar to stinking lovegrass, not only in appearance but also in its provenance and status as a weed in North America. In Wild Urban Plants of the Northeast, Peter Del Tredici mentions two North American natives that can be weedy along roadsides and in vacant lots, sidewalk cracks, garden beds, and elsewhere: E. pectinacea (Carolina lovegrass) and E. spectabilis (purple lovegrass). Last but not least, Eragrostris tef (aslo known as teff) is a commonly cultivated cereal crop in Ethiopia and surrounding countries, the seeds of which are harvested to make injera.

Additional Resources:

Video of the Week:

The Idaho Weed Awareness Campaign has some fun educational materials, including a few puppets, to help teach children about noxious weeds. Mortie Milfoil is a puppet who helps spread the word about the aquatic invasive, Eurasian watermilfoil (Myriophyllum spicatum). Hannah teaches kids about poison hemlock (Conium maculatum). See Hannah’s video below:

Summer of Weeds: Salsify

Picking a favorite weed is challenging. If we dismiss entirely the idea that a person is not supposed to like weeds, the challenge is not that “favorite weeds” is an oxymoron; it is, instead, that it is impossibile to pick one weed among hundreds of weeds that is the most attractive, the most impressive, the most useful, the most forgiving, whatever. For me, salsify is a top contender.

Salsify and goatsbeard are two of several common names for plants in the genus Tragopogon. At least three species in this genus have been introduced to North America from Europe and Asia. All are now common weeds, widespread across the continent. All have, at some point, been cultivated intentionally for their edible roots and leaves, but Tragopogon porrifolius – commonly known as oyster plant or purple salsify – may be the only one that is intentionally grown in gardens today. Its purple flowers make it easy to determine between the other two species, which have yellow flowers.

As it turns out, I am not familiar with purple salsify. I don’t think it is as common in western North America as it is in other parts of the continent. In fact, the most common of the three in my corner of the world appears to be Tragopogon dubius, commonly known as western salsify. Tragopogon pratensis (meadow salsify) makes an appearance, but perhaps not as frequently. To complicate matters, hybridization is common in the genus, so it may be difficult to tell exactly what you are looking at.

western salsify (Tragopogon dubius)

Regardless, salsify is a fairly easy weed to identify. It is a biennial (sometimes annual, sometimes perennial) plant that starts out as a rosette of gray-green leaves that are grass-like in appearance. Eventually a flower stalk emerges, adorned with more grass-like leaves, branching out to form around a half dozen flower heads. Salsify is in the aster family, in which flower heads typically consist of a tight grouping of disc and ray florets. In this case, only ray florets are produced. The florets are yellow or lemon-yellow, and each flower head sits atop a series of pointed bracts which encase the flower (and the forming seed head) when closed. Examining the length of the bracts is one way to tell T. dubius (bracts extend beyond the petals) from T. pratensis (bracts and petals are equal in length).

Illustration of Tragopogon dubius by Amelia Hansen from The Book of Field and Roadside by John Eastman

The flowers of salsify open early in the morning and face the rising sun. By noon, they have usually closed. This phenomenon is the reason behind other common names like noonflower and Jack-go-to-bed-at-noon. Salsify’s timely flowering makes an appearance in Elizabeth Gilbert’s novel, The Signature of All Things: “Alma learned to tell time by the opening and closing of flowers. At five 0’clock in the morning, she noticed, the goatsbeard petals always unfolded. … At noon, the goatsbeard closed.”

The seed heads of salsify look like over-sized dandelions. Each seed (a.k.a. achene) is equipped with a formidable pappus, and with the help of a gust of wind, seeds can be dispersed hundreds of feet from the parent plant. The seeds don’t remain viable for very long, but with each plant producing a few hundred seeds and dispersing them far and wide, it is not hard to see why salsify has staying power.

Open, sunny areas are preferred by salsify, but it can grow in a variety of conditions. In The Book of Field and Roadside, John Eastman writes, “goatsbeards can establish themselves in bare soil, amid grasses and old-field vegetation, and in heavy ground litter; such adaptability permits them to thrive across a range of early plant successional stages.” Wild Urban Plants of the Northeast lists the following sites as “habitat prefrences” of meadow salsify: “abandoned grasslands, urban meadows, vacant lots, rubble dumps, and at the base of rock outcrops and stone walls.” While generally not considered a noxious weed, Tragopogon species are commonly encountered and widely naturalized. Last summer on a field trip to Mud Springs Ridge near Hells Canyon, salsify was one of only a small handful of introduced plants I observed looking right at home with the native flora.

Seed heads of western salsify (Tragopogon dubius) before opening

All that being said, why is salsify one of my favorite weeds? Its simple and elegant form appeals to me. Its gray- or blue-green stems and leaves together with its unique, yellow flowers are particularly attractive to me. And its giant, globe-shaped seed heads, which seem to glisten in the sun, captivate me. Its not a difficult weed to get rid off. It generally pulls out pretty easily, and it’s a satisfying feeling when you can get it by the root. It’s a sneaky weed, popping up full grown inside of another plant and towering above it, making you wonder how you could have missed such an intrusion. The roots are said to be the most palatable before the plant flowers, so if you can spot the young rosette – disguised as grass and also edible – consider yourself lucky. I haven’t tried them yet, but I will. [Editor’s note: Sierra tells me that I have eaten them in a salad she made, but at the time I didn’t know they were in there so I don’t remember what they tasted like.] If they are any good, that will be one more reason why salsify is one of my favorite weeds.

Bonus excerpt from Emma Cooper’s book, Jade Pearls and Alien Eyeballs, regarding Tragopogon porrifolius:

Salsify is often called the vegetable oyster, because its roots are supposed to have an oyster-like flavor although I suspect nobody would be fooled. The long roots are pale and a bit like carrots – they are mild and sweet and when young can be eaten raw. Mature roots are better cooked. Traditionally a winter food, any roots left in the ground in spring will produce a flush of edible foliage.