New Science and Nuisance Plants: How Outdated Nuisance Plant Statutes Inhibit Urban Ecology and Conservation


Urban ecology and conservation have become increasingly important in recent years.  More people than ever before, over 50%, live in urban environments, and that number is expected to reach 66% by 2050.[1]  This, while overall urbanization and degradation of the landscape has increased; over 50% of wetlands in the United States have been destroyed,[2] and, though the forested acreage of the country has largely stabilized, these forests are not equal to their historic counterparts, with over 90% of old growth having been logged[3] and much of what remains fragmented by development to the detriment of the ecosystem and the services they stand to provide.[4]  People are increasingly removed from the environment that sustains them, while that same environment, and the ecosystem services it provides, continues to shrink and decrease in quality.   Indeed, it is in urban areas that the environment and ecology are most important for the health and well-being of those that reside there[5], and yet the challenges faced by the plants and animals there are among the most extreme.

For these reasons, deliberate efforts at urban conservation and the creation of urban ecosystems have become an important piece of greater conservation efforts across the country.  These efforts manifest in a number of ways, ranging from large and small efforts from individuals, municipalities, and non-profit, focused on urban agriculture, the active management of invasive species, the creation of park or preserve greenspaces, and, perhaps simplest and most easily accessible, the cultivation of native garden plots or individuals of ecologically valuable species, such as milkweed in the Milkweed for Monarchs program.

The impact of these native plant gardens should not be understated.  Depending on the nature of the particular garden, they provide a host of health and ecological benefits, making productive often otherwise ecologically valueless lawns or plots which would otherwise be empty or filled with non-native ornamental plants.[6]  Native plant gardens provide habitat where there otherwise is none for a wider range of species than lawns, ornamental plants, or sites cultivating singular species of native plants, helping maintain biodiversity, which brings with it healthier, more stable, more productive ecosystems and ecosystem services.  In addition, healthy plots of native plants tend to utilize less water, decrease erosion, absorb more runoff from and require less fertilizer, and act as sinks for pollution and greenhouse gases.

Despite the easily obtained benefits of such sites, however, their creation is not always so simple for landowners who wish to participate.  There are educational limitations, as certain native plants may require particular planning and care unfamiliar to those seeking to plant them.[7]  Likewise, though often less expensive than maintaining a grass lawn, there are setup and maintenance expenses, not the least of which is owning or having the rights to land that can be planted.   To be certain, there are programs at the federal, state, and local levels which provide aid on these fronts, but these are far from universally available.

Perhaps the biggest obstacle, though, can be state and local laws, particularly nuisance laws, which prohibit, severely limit, or make legally ambiguous the creation of native plant plots on one’s property.  The intent of such laws is to protect the public from noxious or dangerous plants, protect the property of those residing in an area, and, indeed, sometimes to protect the integrity of the local environment.  However, these laws are often outdated, poorly or ambiguously written, omitting modern notions of ecology and botany to reflect the true nature of the labeled plants, and serve to complicate urban conservation efforts by providing reason for would-be conservationists to be unnecessarily restricted or uncertain about the legality of their efforts, giving them the option of proceeding and risking fines or abatement of their gardens, or abandoning their effort altogether.  This is the case even when a bad statute is left largely unenforced, as exemplified in the example from St. Louis, Missouri below.  This is an unacceptable but easily remedied state of affairs, resolvable with relatively simple amendments which preserve their public safety and property purposes to such nuisance laws by redrafting them with clarity, specificity, and modern notions of conservation, ecology, and botany in mind.

The Scenario in St. Louis

            St. Louis, Missouri: City Code of Ordinances Section 11.04.040- Public nuisance—Vegetation designation.[8]

“Russian, Canadian, or common thistle, wild lettuce, wild mustard, wild parsley, ragweed, milkweed, ironweed, poisonous plants or shrubs, and all other unattended vegetation and noxious weeds which have attained a height of seven (7) inches or more growing or being upon any lot or lands within the City, and unattended growths of shrubs, trees, and seedlings, which in the opinion of the Commissioner of Forestry, are unsightly and which may impede the clearing of any lot or lands within the City contrary to the general purpose of this chapter, are hereby declared a public nuisance. Every owner, occupant, or person in control of any lot or land within the City shall cause such lot or lands to be kept free from such noxious weeds and vegetation by destroying them, by cutting or spraying with a chemical compound approved by the United States Department of Agriculture and the United States Environmental Protection Agency for the destruction of weeds, or by digging under, or by any other method approved by the Commissioner of Forestry.”

St. Louis, Missouri: City Code of Ordinances Section 11.04.080 – Abatement procedure—Authority.

Weed or debris nuisances may be abated immediately as follows:


Nuisances described in Section 11.04.040 on properties whose owners have been served with notice under Section 11.04.070B shall be abated by the Forestry Commissioner without further notice.


In 2017, a situation arose in the City of St. Louis in the enforcement of St. Louis Code section 11.04.040.  A homeowner had on their land an area they considered a natural garden, and maintained it for the claimed purpose of encouraging the growth of native plants and providing habitat for native animals, especially pollinators.  They received notice from the city about pending abatement of that area, per St. Louis Code section 11.04.090, if she did not mow it, as it was “unsightly” and exceeded the height and noxious plant restrictions in section 11.04.040.  However, mowing the area, the homeowner claimed, would destroy the native plants they sought to cultivate.  Specifically, the plot contained a milkweed species preferred by monarch butterflies- a species which the city itself maintained on its own land, encouraged residents to grow, and gave out to residents as part of the Milkweed for Monarch program.[9]

Without speaking to the merits of either the landowner or the city’s claims, it was discovered that St. Louis Code section 11.04.040, last amended in 1986, deemed “milkweed” and any other “unsightly” plant which has “attained a height of seven (7) inches or more” a public nuisance.  Notably, most milkweed flowers between twenty-four and seventy-two inches, effectively making non-nuisance growth of milkweed in the city impossible.  Also notable, this meant the city itself was not only encouraging and enabling milkweed growth in violation of this statute, but was actually violating it on its own land in the numerous milkweed gardens it maintained.  Yet it was, in the case of this homeowner, seeking to enforce that same statute, in part in response to the homeowner doing precisely the same act- growing milkweed in excess of seven inches in height.

Ultimately, the City of St. Louis did not abate the landowner’s garden.  After discussion and negotiation with the city, it was agreed that, so long as the garden was maintained, it would not be mowed.  However, this result was only obtained after stress to the landowner, calls to lawyers, and the expenditure of city employee time and resources.  It is not hard to imagine a scenario in which a less determined or less passionate landowner would permit their garden to be mowed rather than spend time and energy contacting lawyers.  This, this essay suggests, is an unacceptable and readily resolvable issue frequently found in outdated and poorly written municipal nuisance plant statutes, which too often fail to consider modern notions of ecology and botany, while providing would-be urban conservationists a roadblock to their own environmental efforts.

At best, the inconsistency between St. Louis City statute and city policy provided an ambiguity for residents: the city was simultaneously cultivating milkweed while telling its residents to do the same, while the plant remained legally classified as a nuisance and the City retained the right to abate it, even if it was not a right they typically exercised.  However, at worst, section 11.04.040 and other statutes like it have a deeper effect of discouraging urban ecology and at home conservation efforts in a more general sense, either by making the act outright illegal, by not providing clear standards with regard to what is acceptable or outlining protections for the growth of native plants over non-native, and of benign or minimally dangerous plants over the more dangerous.

There are other issues with section 11.04.040.  The definition of what is “unsightly” is left to the discretion of the City Commissioner of Forestry, with no additional statutory guidance to suggest by what other criterion such a determination will be made, making the issue all the more vague for any prospective conservationist landowner.  Likewise, section 11.04.040 lists by common name a number of plants which are a nuisance per se: “Russian, Canadian, or common thistle, wild lettuce, wild mustard, wild parsley, ragweed, milkweed, ironweed.”[10]  Though only nine plants are listed, in doing so the statute effectively bans the growth of hundreds of different species within the city- over 140 plants go by the common name of milkweed alone, some of which, again, are cultivated by the city itself.[11]

A glimpse at recent history and botany reveals why the named species are deemed a nuisance.  They are largely fast-spreading species, quick to take over a space if left unchecked, often non-native and invasive in nature and typically growing in a disorganized, leafy manner I suspect many would call “unsightly.”  Thistle tends to be viciously thorny, ragweed is a common agitator of seasonal allergies, and wild lettuce, wild mustard, wild parsley, and milkweed all contain species with potentially toxic or irritating properties if ingested or touched.  The issue with section 11.04.040 as written is that the fears used to justify the banning of these plants are largely overstated and unjustified, and blanket common name bans target plants under that same name which do not have the properties which justify their exclusion.

This is not to suggest that banning certain plants as a nuisance is not justified.  Indeed, I think it likely that many conservationists and ecologists, to the inclusion of myself, would agree with the spirit of the statute and a number of the prohibitions it contains.  Of the named thistle species, none are native, all are ecologically noxious, and all are thorny in nature.  The wild lettuce section 11.04.040 probably intended to target, Lactuca virosa, contains a variety of chemicals which have a variety of potential effects if ingested, one of which mimics opiates, and so may be of legitimate concern.  Wild mustards (indeed, the plant most commonly labeled as ‘wild mustard,’Sinapis arvensis) can be devastatingly invasive, non-native, and potentially quite toxic, while offering little ecological value to North America.[12]  Wild parsley, or giant hogweed or Heracleum mantegazzianum, is invasive, non-native, and extremely toxic went contacted, resulting in severe rash and skin damage if handled improperly.  There is no shortage of ragweed, which manages to thrive even in the highly degraded wooded areas in the region, and the harm its masses of pollen generate is very real and traceable, and so defending its place in urban environments sans other ecological benefit is a losing battle.

However, there are many plants which are either intentionally banned or have unclear status per 11.04.040 which have grossly overstated potential dangers or none at all, and which do indeed stand to provide ecological value which exceeds any real risk.  There are flowering native plants which do not share the chemical nature of Lactuca virosa which fall under a broader ‘wild lettuce’ label, the ban of which cannot be justified from a public safety perspective alone.[13]  The wild mustard of the Brassicaceae family are varied, with harmless and ecologically positive species sometimes included in the umbrella of ‘wild mustard.[14]  The same is true of wild parsley; though many native parsley species have a vaguely opportunistic nature in low quality ecosystems and share the skin irritant properties of the non-native giant hogweed, the effect is much less severe and the risk of even giant hogweed are grossly overstated to include risks such as blindness, which modern health research on the plant suggests are false.[15]  Some plants of the ironweed genus Vernonia– which includes over one-thousand species, some native to Missouri[16]– have potential (mostly non-toxic and potentially positive) medical impacts if consumed, but many do not, and yet all are banned under section 11.04.040.

Milkweed is not excepted from this unfair blanket treatment.  Milkweed in all of its native varieties does contain certain toxins, galitoxin, which is dangerous to both humans and animals if consumed.[17]  However, the risk to humans only exists if large quantities are consumed, a prospect unlikely to occur by accident or at the hands of a careless, curious child due to the volume required to produce any lasting ill effects and the unappetizing, bitter nature of the plant- a mechanism designed to signal precisely its toxicity to any would-be consumers.[18]  Likewise, wild animals have evolved around the toxic risk, and are not likely to consume a plant they recognize as a non-viable source of food.[19]  Further, though domesticated animals may endure some risk should they consume the plant, these risks are primarily centered on penned herbivorous livestock of which there are few in urban areas, not domestic cats, dogs, or even chickens so long as the yards in which they are contained do not contain an overabundance of the plant.[20]  This is all to say that the risks of the plant that would perhaps make it a nuisance are overstated at best and inaccurate at worst, and so its prohibition cannot be justified.  The City of St. Louis, despite section 11.04.040 seems to agree with this perspective if their participation in the Milkweed for Monarchs program is any indication.[21]  Yet the statute, including its prohibition of milkweed, remains in effect and unamended, and, if largely unenforced, apparently still available to enforce if the City so chose.

To summarize, it is not the bans in sections 11.04.040, per se, that are problematic in terms of urban ecology, but the manner in which it is done.  Common names are, by their very nature as accessible labels for ecological laypersons, overbroad and inconsistent, and deeming a plant a nuisance by its common name leaves significant room for ambiguous interpretation of the statute or overbroad application that makes illegal plants with no real nuisance character.  Likewise, plant ecology is a more complicated subject to manage than was recognized at the time this section was written.  On its face, the removal of all plants with even vague toxic natures or irritating properties may seem a valid policy which serves the public’s wellbeing, but this is only the case if the intrinsic, economic, and health benefits associated with healthy and abundant ecological systems are ignored.

There are four readily available, non-exclusive solutions to section 11.04.040’s problems that allow the statute to serve the public safety purpose for which it was intended while eliminating any overbroad coverage or ambiguity that may unnecessarily hamper urban ecology.  The first is to delineate clearer standards requisite for abatement.  As it stands, the statute permits city abatement of lands if any of the prior-mentioned species are present, of “all other unattended vegetation and noxious weeds which have attained a height of seven (7) inches,” and any other “unattended growths of shrubs, trees, and seedlings, which in the opinion of the Commissioner of Forestry, are unsightly and which may impede the clearing of any lot or lands within the City.”  No additional clarification is available, either in statute or publicly available administrative guidance on the City of St. Louis Forestry website, although the ability to report high grass or weeds is present online.[22]  No express guidance on what is considered ‘unsightly,’ nor to what degree plants and shrubs must be ‘attended’ are available, though such guidance is available for trees.[23]  If the prevalent mindset is one that favors a manicured lawn, perhaps what exactly is meant by these sections is more obvious: likely well-trimmed ornamental grass, perhaps dotted with a trimmed tree or bush, with all other plants contained in a walled garden bed and kept so as to appear orderly and inoffensive.  However, even ignoring the fact that commonly held notions of what a lawn should look like are not always consistent with the appearance of even well-maintained native habitat, nor consistent from individual to individual, the fact remains that this is not articulated in the statute, nor on the website of the city official who has apparently been granted discretion to interpret and then enforce that statute.  At best, what is and is not permitted, and at what point one can expect an abatement notice is ambiguous, unclear.  Regardless of whether the city wishes to embrace native plant gardens and urban conservation, there is currently an issue of clarity that need be addressed.

The second is to simply remove needlessly classified plants from the nuisance list, milkweed being perhaps the most obvious and highest priority in section 11.04.040.  This should of course, be done in consultation with relevant experts: ecologists, botanists, and public health experts.  Such a consultation would reveal that fears over milkweed as a danger to children, pets, and other urban and suburban residents are overstated and largely unrealistic, and on such a finding the public safety justification for its prohibition cannot be maintained.  To be certain, the risk is minimal, likely overshadowed completely by the ecological value of cultivating the plant- a perspective which, once again, the City of St. Louis seems to agree.  A modern analysis of certain other listed plants seems likely to reach a similar conclusion.

The third is to, rather than utilize common names when labeling plants as public nuisances via statute, utilize the more specific scientific genus and species names, or at least clarified statements as to what exactly is meant by a given common name.  Common species names are inherently problematic when codified into law as in section 11.04.040.  By their nature, they are non-specific, often including a number of sometimes disparate and potentially even unrelated species under the umbrella of a particular common name, with what exactly is meant to be included changing over time and from region to region.[24]  It seems doubtful that the City of St. Louis, in passing section 11.04.040, intended to prohibit the hundreds of species a literal reading of the statute would require, some of which do not share the same noxious, hazardous, or invasive nature that justifies the prohibition of their identically-common-named relatives.  It is possible, of course, that that was the intent, and that these hundreds of related (and sometimes not related) species were all deemed public safety risks.  Even in that case, though, that intent would only further signal the need for revisiting the statute, as such a broad reading can hardly be justified, nor is it currently clear that it is in fact the case.

Scientific names are designed to be precise and stable.  A genus name refers to only the species in that genus, and a full species name can refer to only one species, with only infrequent changes which occur only when supported by genetic or biological research.  Using scientific names ensures only the species intended to be covered are actually covered by a statute, removing ambiguity for residents over time and narrowing the scope of the statute from needlessly impacting unintended species- that is, those without particularly noxious or hazardous or otherwise non-native or invasive characteristics.  This makes for a clearer law which is more effective at its intended purpose and imposes the least burdensome restrictions on those who must adhere to it.  Failing the use of scientific names, more specific common names should be utilized, as with the thistles listed in section 11.04.040 and with the prescribed nuisance plants in Ballwin, Missouri’s Code of Ordinances section 29-6.[25]

The fourth is to provide either exceptions for native plants generally or certain native plants, or to provide different criteria through which to determine non-noxious native plants are a nuisance.  Permitting landowners to cultivate native plants above the maximum permitted height and regardless of common name prohibitions so long as some minimum prescribed degree of maintenance is performed would effectively resolve any issues nuisance statutes such as section 11.04.040 have in chilling urban conservation, while still serving the public safety interest in controlling noxious and hazardous plants.  This is not to suggest that particularly dangerous or invasive native plants could not still be named as prohibited.

This would be particularly effective in conjunction with a blanket (unless otherwise specified) prohibition on the cultivation or toleration of non-native invasive species; it seems contradictory and illogical that a native milkweed species be prohibited in all circumstances when it is wholly permissible to cultivate a managed plot of invasive honeysuckle, bamboo, or Paulownia tomentosa (princess tree).  Such a statute would minimize the needed language to detail what is and is not permissible, while maximizing the ecologically valuable plants that can be legally grown, and limiting the growth (and so the spread) of detrimental invasive species.  The implementation of any part or all of these suggestions would result in a more effective statute, both for the people of St. Louis who must abide by it, and for the urban ecology it seeks to control.

Other Nuisance Plant Statutes

Neither the experience of the St. Louis landowner with laws like section 11.04.040[26] nor section 11.04.040 itself are unique in the St. Louis Metro Area or elsewhere.  Even in the St. Louis Metropolitan Area, the City of St. Louis may have a particularly troublesome nuisance plant statute in section 11.04.040, but many municipalities on the Missouri side of the metro area (St. Louis County) have on the books nuisance plant statutes that share at least some of the same deficiencies as the city itself, and each could be fixed in much the same way without jeopardizing public safety or the welfare of these communities in any tangible way.

Model statutes which more or less apply the solutions presented in this paper exist, already written and in effect, requiring only minimal redrafting to account for local issues and ecology.  Wild Ones[27] pushes for a model nuisance plant statute drafted by the Native Plant Preservation Coalition of Wisconsin.[28]  This model statute protects the growth of native plants not expressly banned for some valid reason, while at the same time prohibiting by both common and scientific names a number of species prohibited due to their invasive or noxious natures.[29]  Additionally, where it limits the height of plants, it expressly only limits the height of turf grass- not grasses or plants grown for other purposes than as turf.[30]  Likewise, it does not leave the municipality at the mercy of irresponsible residents: landowners which permit the creation of hazards or growth of overgrown grass or prohibited plants on their property can, and only in those circumstances, still be forced to properly maintain their land or risk municipal action.[31]

In the St. Louis Metro, some municipalities have indeed adopted reasonable, perhaps even excellent nuisance plant statutes.  Chesterfield, Missouri maintains a statute that incorporates protections for managed stands of native plants, a specific list of prohibited plants, and buffer zones between plant stands and the property of others- a justifiable and perhaps necessary concession to those who dislike neighboring anything but turf if it permits otherwise fairly unrestrictive native plant management.[32]

Clarkson Valley, Missouri maintains a statute which expressly prohibits invasive and noxious plant species, lists some which are included (but not all, and though not with scientific names, at the least with more particularized common names than the City of St. Louis statute), and exempts sites used for prairie or wetland and wooded sites from restrictions on growth so long as no hazards are created.[33]

These are easy fixes for unjustifiably troublesome statutes.  At the local level is where much of the environmental stress we currently face can be most readily addressed, and the development of healthy, productive greenspace in increasingly urbanized areas is one of the simplest and most accessible means through which anyone can have a positive impact- so long as local law allows.  Examining old codes based on outdated perceptions and knowledge which create obstacles for beneficial activity is a duty residents in any city have, all the more so when it relates to pressing concerns like environmental issues.


[1] Govind Singh, Urban Ecology & Ecosystem Inputs – Need of the Urban Era, Urban Ecology (5 October, 2014),; United Nations 2007 World Urbanization Prospects: The 2007 Revision, United Nations (2007),

[2] Thomas E. Dahl, Wetland Loss Since the Revolution, National Wetlands Inventory: Fish and Wildlife Service,

[3] David Allan, Global deforestation, Global change program, University of Michigan (1 April 2014)

[4] Report on the Environment: Forest Fragmentation, Environmental Protection Agency, file:///C:/Users/tatsw/Downloads/forest-fragmentation.pdf

[5] See World Health Organization publications ( and the vast multitude of others.

[6] Why Native Plants Matter, Audubon,


[8] See

[9] This program intends to have the city cultivate milkweed in gardens and help residents grow milkweed on their property in order to help monarch butterflies reproduce during their migration- in direct violation of the statute in question.  See

[10] St. Louis City Code Section 11.04.040

[11] Supra note 9

[12] Plant Assessment Form: Sinapis arvensis, California Invasive Plant Council,

[13] See

[14] See

[15] Friend or Foe: Giant Hogweed and Its Look-alikes, Home, Yard and Garden Pest, 8 (11 June, 2010), University of Illinois,

[16] See

[17] Sara BhaduriHauck, Toxic Plant Profile: Milkweed and Dogbane, University of Maryland (9 Oct. 2015),

[18] Id. 

[19] Id. 


[20] Id.

[21] Supra note 9

[22] See

[23] City of St. Louis, Ordinance 68607 City of St. Louis Forestry Ordinance, 6 Apr, 2010,

[24]  A Word About Species Names…, Indian River Species Inventory, Smithsonian Marine Station at Fort Worth,


[25] Ballwin Code of Ordinances, Section 29-1,

[26] Doug Miner, Woman defends native plants in her yard; city says clean it up, 40 South News (9 Aug., 2016),

[27] See here:


[29] Id. 

[30] Id. 

[31] Id. 

[32] City of Chesterfield Code of Ordinances, Section 20

[33] Clarkson Valley Code, Article II, Section 215,,%20MO_%20Whole%20Code.pdf

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