People and Poison Ivy


An ecological, social, and natural scientific discussion
about understanding and solving a painful problem

Umar K. Mycka, Poison Ivy Horticulturist
Jacob Pilon, MSW RSW



Poison ivy plants in your home environment often cause a medical emergency which arises from and is based outside in your garden and that requires a horticultural solution.

A solution is to remove the entire plant so that the problem is mitigated.
This approach crosses many professional boundaries: dermatological, social science, plant biology, and horticultural.
An added handicap is that the plant type is found in North America and not Europe so although it was studied in the colonial period as a horticultural oddity, it was not a threat to people living in Europe so it has not been carefully analyzed for its  threatening nature and how people can avoid it.

This article examines from a social science and ecological science vantage point the variety of approaches to keep people and poison ivy a safe distance from one another and what can be further done under the present challenging conditions.

In a nutshell

People know of and fear the dermatitis caused by poison ivy but we don’t clearly know how to identify the plant mainly due to its malleable form and our incomplete and outdated identification cues.

A comprehensive interdisciplinary examination could raise our current antidotal discussions to solid useful facts and information.


From the Evergreen State of Washington to New Mexico, the Land of Enchantment, a creeping menace (Toxicodendron rydbergii) is invading the forest floors and spreading through backyard and landscape shrubs, tormenting more and more people. And from the Pine Tree State of Maine to the Palmetto State of South Carolina, it disguises itself as an innocent vine (Toxicodendron radicans), yet also, with a vengeance, mercilessly inflicts its ferocity upon many.  Canadians from the Million-acre farm of Prince Edward Island to the Wild-rose country of Alberta are liable to feel the sting.  Even Mexico can’t escape. Neither can Guatemala, Bermuda or the Bahamas.

This nemesis continues its devastating march, unchecked. Even though it inflicts severe suffering on people of all ages, no rule of law has been created to capture it, punish it, or end its tyranny. So it seems to be left up to solitary individuals to identify this poisonous stalker and to avoid touching it. But this is easier said than done. Why have we failed for so long to defeat this noxious invader? Why haven’t we been able to identify or understand it?

The ecological, social, and natural scientists have for some time been engaged in a serious conversation to seek solutions to this spreading challenge. Hopefully a collaborative effort will lead to a greater understanding of poison ivy, and help us to say goodbye to this Itch!

Just what is hampering us from finding a solution?

The traditional poison ivy image we have of ‘leaves of three’ is somewhat vague. And the elusive masquerader shows us that ‘Leaves of Three’ is not always me!

Hapili, the Human and Poison Ivy leaflet interface


Whats Holding Us Back?

On this one point many experts from botanists to dermatologists agree. They know what the plant looks like and follow the ‘touch-me-not’ rule. But for the rest of us, this is obviously easier said than done. One major reason is our lack of ability to identify what the leaves really look like. Another is that the knowledge we have about its complicated growth strategy is not only limited and incomplete, but also extremely outdated. If we don’t know why or how it is on the increase, we just follow whatever folklore has been passed on to us, while the poison ivy ignores our beliefs and brazenly continues on its relentless marathon of growth. Most of us don’t even realize the part we are unknowingly playing in helping it to spread out of control over the North American continent.


Ask A Poison Ivy Horticulturist

What Does it Look Like? How Does it Grow and Spread?

If you had a chance to pick a poison ivy horticultural expert’s brain, what would you want to know? Here are some possible questions we thought might come up:

How can I identify the leaves and vines (to avoid touching it)?

How can I understand its growth pattern (so I can halt it in its early stages)?

What can you tell me to help me understand its complexity and end my perplexity?


How can I identify the leaves and vines?

First we need to look at the poison ivy leaf structure itself, even though each stem has three separate growths, called leaflets, together those three connected leaflets comprise one single leaf. The genius of the poison ivy plant is that a single leaf splits into one terminal leaflet with a leaflet stalk (called a petiolule), plus two lateral leaflets and a leaf stalk (or petiole). Think of how our hand ends in five fingers (each finger unique), but it’s still our one hand.

It is no wonder that the old saying, “Leaves of three let them be,” only gets us so far. A more useful saying for identification might be “Leaflets three, must look like me,” So to accurately identify the plant, we have to go further in our analysis. We have to examine the leaves more closely and see that they are not identical to one another. And yet like people, they do share similar broad characteristics. You can see in (Figure 1) how the terminal leaflet could be compared to our head attached to the neck (petiolule), while the two lateral leaflets are like two arms attached to the body (petiole).

The growing environment affects the shape of the plant leaflet’s edge. The edge margins of the leaflet are determined when the leaflet is in the formative embryonic stage. They develop to a particular and specific combination of shapes based on conditions the leaflet anticipates it will encounter when it emerges. Just as many things in nature, including people, grow and change to best suit their basic needs, the leaflets position themselves in whatever pose will best facilitate the vine to grow in a desired direction.

Poison ivy leaflets' different margin edge shapes


How can I understand its growth pattern?

Poison ivy depends upon the sun to calculate its best possible growth path. The variations we see among leaf shapes actually reflect stages of growth at each particular place along the plant’s growth trajectory.

But poison ivy is not limited to creeping along the ground. There is a climbing variety, a very determined type, which is essentially a plant on a mission. Starting from a seed, it must struggle to find its way to a suitable vertical object (like a tree, fence, rock or structure) and climb to a height where it is able to gather the amount of filtered light needed to grow into a mature plant. In fact it is actually navigating and climbing through its environment towards its ideal height. Once it reaches the point where it can begin the life of a mature flowering plant, it will stop growing upward and begin branching out horizontally.

If we reflect on this process it makes a lot of sense because the poison ivy plant invests energy and a full season’s growth to sending ground vines towards its vertical target. Its very life and future depend on at least one of them succeeding.

Botanical sketch of 2 year old poison ivy plant showing traveling ground vines


 How can I better understand Poison ivy’s complexity and end my perplexity?

(Figure 4)

How does it know to do this, find its place in the Universe? There is a mathematical approach called triangulation that calculates how two known factors can be used to predict the course of an unknown factor. In this case, the two given parts of the triangle are (1) the sun’s path through the sky and (2) the distance and height of a nearby tree. In the process of traveling from the position of the seed’s germination until the ground vine contacts a tree and grows upward and reaches an ideal height, these two known factors seem to influence the Poison Ivy plant, causing it to follow the uncertain yet fairly predictable path, just as the snow geese always fly south in the winter.

Visual indicators of the navigation of a poison ivy vine

So we see that far from being a plant that springs up out of nowhere, each step of poison ivy’s growth is part of a carefully executed plan. This is a beginning in our exploration of the full complexity of its growth strategy.   
Factors Contributing to the Growth Spurt

Contrary to popularly held urban myths, poison ivy is usually not spread onto your property from your neighbor’s unkempt yard, but rather has more likely been introduced by a very specific method: the birds that perch and flock around your yard. Both migratory and over-wintering birds actually eat poison ivy fruit and then disseminate the seeds across the North American continent (the Arctic and tundra regions notwithstanding). Moreover, the recent popularity of bird watching and feeding as a hobby attracts these birds to yards all over the country. So, not only are we watching the birds, but the birds are also watching us! As they perch on feeders and the rails of outdoor decks, they drop the poison ivy seeds right there, thus creating prime spots that eventually establish growth areas for new developing plants.

A Prairie Warbler eats poison ivy fruit

Another significant influence in the fast spread is the landscaping decisions made by both individual homeowners and community planners, which almost promises a large amount of poison ivy growth within an area or site. Take for instance, the shared and often wooded or fenced borders between each subdivision lot in the sprawling suburbs. These provide an excellent habitat for poison ivy growth. And since the suburbs have multiplied and spread exponentially, so has the poison ivy.  The old careful personal hand-gardening habits once used by landscapers, homeowners, and small gardening companies run by sole proprietors have more and more been abandoned, thus giving way to speedier and often neglectful techniques to maintain residential properties and remove poison ivy.

Nowadays this personal touch has been largely replaced with what could be referred to as ‘flash gardening’, in which large crews of laborers unskilled in good horticultural practices quickly blitz through properties using power tools. This flash gardening all too often leaves untouched the property edges and anywhere else that power mowers or line trimmers cannot easily access, allowing poison ivy and other vines to grow unnoticed and unchecked. And because there is usually an additional charge for a crew to clean up the edge areas and hard to reach places, homeowners often just let them grow wild. Now, since it takes about four years for poison ivy to grow from a seed to the point of flowering and producing fruit, it is easy to see how quickly and easily this plant can make its unwelcome and overwhelming presence felt. And once it’s in, it’s hard to get rid of!

If we go a step further and look at this issue from a global perspective, we begin to hear a lot of voices citing climate change as one influencing factor in increased poison ivy growth. Studies that have shown an increase in ambient atmospheric carbon dioxide of 22% since the late 1950’s, (IPCC, 2001)[1] suggest that poison ivy growth may have taken advantage of the available carbon in the air to significantly increase its growth (Ziska et al, 2007)[2].

In addition to the factor of climate change, both poison ivy’s own process of how its seeds are spread and its growth strategy have a strong impact on people’s lives and how they interact in their personal and community spaces.


Search for understanding

Lately, many opportunities for people to become really educated about poison ivy have surfaced, and can be generally classified into two categories: formal academic botanical studies and informal learning.

Formally, there have been a handful of large-scale academic studies undertaken that provide accurate and insightful knowledge on poison ivy and poison oak (Toxicodendron diversilobum) growth in North America; unfortunately these papers are not widely distributed, nor well read. And all too often they are not really understood by those outside of the scientific disciplines. (See footnote [3] for a listing of some recommended studies)

Informally, education is prevalent about poison ivy in the form of traditional folksy rhymes, from the early days of the United States when the country’s economy was mainly agricultural, and the majority of the population lived in small rural communities. Summer vacations and camps presented opportunities to learn to identify poison ivy. But since many vacation spots in the mountains and rural areas of North America (prime poison ivy country) have fallen from favor, the once popular cabins and motor inns have been abandoned.

In the early decades of the 20th century, poison ivy identification was essentially a first-hand, orally passed-down skill by older friends and relatives to the uninitiated usually on a one-on-one basis. Before the days of the internet and media communication, it was a common enjoyable pastime to identify, study, and memorize the names of wildflowers and other plants, including poison ivy. (Along with making mud pies!)

This kind of informal, anecdotal poison ivy education, although it was popular and easy to understand, no longer works in our present day circumstances where we lack experienced tutors with accurate knowledge about what poison ivy looks like and where it grows. These crucial yet missing components have left us without good solutions to the identification problem.


People and Poison Ivy: looking beyond personal problems toward a wider understanding

It’s easy to see that this lack of social education, in addition to the other multitude of factors we have discussed, has spawned a near perfect storm for poison ivy growth in yards and community spaces all over North America. And this is no tempest in a teapot. Real suffering, fear, and self-blame have been inflicted on many who have touched this allergy inducing plant.

Largely due to this wide-spread oversimplification and inaccurate perception of what poison ivy looks like and how it grows, those unfortunate enough to have come in contact with it in their very own yard often come away from this experience with suffering and deep feelings of self-recrimination, expressing thoughts such as “I should have known better,” and “I should have been able to avoid it!”  They are prone to personalize the entire confluence of factors that led to their poison ivy experience, even though they more than likely had nothing to do with it and had no way of identifying or avoiding it. It’s unfortunate that the needed and necessary information was not accessible --or easily comprehendible-- to them.

We must no longer tolerate the unchecked growth of poison ivy in human spaces. All too often its effects bring about social isolation, as well as profound social stigma for people afflicted with the rash. Not only do they have to deal with pain and possible disfiguration, but can develop serious complications from underlying health conditions. Some of these experiences have even resulted in people carrying physical scars and fostering a fear of plants, gardening or even enjoyment of the outdoors.


So given these circumstances, what’s to be done?

Given all this, how then can we as individuals, professionals, and communities come together to begin addressing appropriate actions to provide relief and remedies for ourselves and our neighbors?

We recommend that steps be taken for more accurate and statistically analyzable data to be collected about the before and after effects of poison ivy on individuals (in terms of education and awareness of the plant both before and after contact). Whether this information could be collected in the form of a standardized survey outlining the physical, emotional and social impacts of poison ivy is a question that needs further discussion, but regardless of the format we believe that gathering such information is an important step towards developing accurate systems of response to the problem through a collaborative, interdisciplinary intervention.

We also invite readers to further educate themselves about poison ivy, its characteristics and identifying features. It will help if many more will join in the conversation on how best to address the multiple challenges that this complex and widespread species presents.



1. IPCC (Intergovernmental Panel on Climate Change). 2001. Climate Change 2001: The Scientific Basis. JT Houghton, LG Meiro-Filho, BA Callander, N Harris, A Kattenberg, and K Maskell, eds. Cambridge, UK: Cambridge University Press. 572 p.

2. Ziska LH, Sicher RC, George K, Mohan JE 2007. Rising atmospheric carbon dioxide and potential impacts on the growth and toxicity of poison ivy (Toxicodendron radicans). Weed Science 55: 288-292.

3. Mohan, JE, LH Ziska, WH Schlesinger, RB Thomas, RC Sicher, K George, and JS Clark. 2006. Biomass and toxicity responses of poison ivy (Toxicodendron radicans) to elevated atmospheric CO2. PNAS 103(24): 9086-9089.

4. Gartner, Barbara Lachenbruch. 1990. Appendix, The logistics of working with poison oak. 132-162, in Consequences of the vine vs. shrub growth forms for biomechanics, growth, and hydraulic architecture of western poison oak, Toxicodendron diversilobum. (PhD Dissertation) Dept. of Biological Sciences; Stanford University. 162 pp.

5. Gillis, W. 1971. The systematics and ecology of poison-ivy and the poison-oaks (Toxicodendron, Anacardiaceae). Rhodora 73:72-160, 161-237, 370-443, and 465-540.

6. Gillis, W. 1975. Poison-ivy and its kin. Arnoldia 35:93-123.

7. WL Epstein, MD, and VS Byers, Ph D, Poison Oak and Poison Ivy Dermatitis - Prevention and Treatment in Forest Service. USDA For Serv Equip Dev Ctr Pub. 8167 2803, Missoula, MT.

Other articles related to the dissertation in Item 4:

Gartner, BL, C Wasser, E Rodriguez, and W L Epstein. 1993. Seasonal variation of urushiol content in poison oak. American Journal of Contact Dermatitis 4:33-36.

Gartner, BL. 1991. Structural stability and architecture of vines vs. shrubs of poison oak, Toxicodendron diversilobum. Ecology 72:2005-2015

Gartner, BL. 1991. Relative growth rates of vines and shrubs of western poison oak, Toxicodendron diversilobum (Anacardiaceae). American Journal of Botany 10:1345-1353.

Gartner, BL. 1991. Is the climbing habit of poison oak ecotypic? Functional Ecology 5:696-704.

Gartner, BL. 1991. Stem hydraulic properties of vines vs. shrubs of western poison oak, Toxicodendron diversilobum. Oecologia 87:180-189