Poisonous to Touch Weed Series: Poison Ivy (Toxicodendron radicans and Toxicodendron Rydbergii)

By: Kimberley Pacholko

Eastern Poison Ivy, (Toxicodendron radicans) and Western Poison Ivy (Toxicodendron Rydbergii ) are important plants to learn how to identify for personal safety. Touching any part of this plant can cause a painful itchy rash with red swollen skin and painful blisters. I have had the miss fortune of being caught twice by this plant and can testify to how unpleasant the reaction can be. The skins reaction to contact with poison ivy is actually an allergic reaction to the urushiol oil contained in the plant. This oil is so potent that only one nanogram (billionth of a gram) is needed to cause a rash (Gov. of Canada 2016). How severe a reaction you have will depend upon how much of the oil you got on yourself, how thick the skin is on the area that came in contact with the oil and how sensitive you are to the oil.

Identification Of Poison Ivy

Overall Growth Habit: Eastern Poison ivy grow as aerial vines with thick woody stems that may climb from 6 to 10 m (6.5 to 11 yards) high on trees, posts, or rough surfaces (Gov. of Canada 2016). It can also grow as vines that trail along the ground with upright leafy stalks 10 to 80 cm (4 to 31.5 inches) high (Gov. of Canada 2016) or as a small shrub 30-120cm (1-4′) tall. Western Poison Ivy grow as a low growing shrub to a height of about 50-100 cm (20-30 in ) depending on location.

Leaves: The compound leaves of poison ivy have three pointed leaflets, thus the saying, sets of three let them be. The leaflets vary greatly in size, from 8 to 55 mm (1/10th” – 2″) in length (Gov. of Canada 2016). The stalk on the middle leaf is always longer than the two side leaves and the leaf edges typically have a few large teeth with rounded edges (not many small teeth or pointed) but they may also be smooth (entire), or anywhere between. The leaves also have a sharp edge that can easily cut skin. The leaves are arranged alternately up the vine.

The colour of the leaves depends on the time of season. In the spring, the leaves appear reddish and often shiny. In summer they are varying shade of green that may appear shiny or matt, turning to various shades of yellow, orange, or red in the fall.

Eastern poison-ivy (Toxicodendron radicans) Photo credit: Paul Wray, Iowa State University, Bugwood.org
Western poison ivy (Toxicodendron Rydbergii) Photo credit: Dave Powell, USDA Forest Service (retired), Bugwood.org
Eastern poison-ivy (Toxicodendron radicans) Photo credit: Terry S. Price, Georgia Forestry Commission, Bugwood.org
Eastern poison-ivy (Toxicodendron radicans) notice the hairy looking arial roots growing off the vine. Photo credit: Joseph LaForest, University of Georgia, Bugwood.org
Eastern poison-ivy (Toxicodendron radicans) notice how the leaves are a bit shiny. and new leaves are reddish in colour. Photo credit: Ohio State Weed Lab , The Ohio State University, Bugwood.org

Stems: may have a reddish tint and the middle leaflet stem is always longer.

Vines: The vines of eastern poison ivy are thick and woody and are covered in thin roots that help anchor the plant to what ever structure it is trying to climb eg: a tree trunk. These thin roots make the vine appear hairy. Old vines can be up to 15 cm (6″) thick.

Flowers: Poison ivy typically flowers in spring, April through June (sometimes as late as July), depending where it is located and whether it is from seed or established vine. “The flowers appear in clusters 5-12cm (2-5″) long. They are attached where the leafstalk meets the stem. Individual flowers are greenish white and only 3-6cm (1/8-1/4″) across” (Wertz, B. A. 1914).

Roots: Poison ivy roots seldom go below 12 inches deep, but they can spread up to 20 feet wide below the surface, while their vines clamber up to the tops of trees (Wertz, B. A. 1914).

Berries: The flowers develop into berries over the summer and by fall clusters of white berries, that are round and waxy, will become noticeable. The size of the berries ranges from 3 to 7 mm (.12 to .28 inches) in diameter (Gov. of Canada 2016). The berries often persist over winter, a good food source for the birds who are not bothered by the urushiol oil.

Look-Alike Plants

  •  Hog-peanut or ground bean (Amphicarpaea bracteata): Have sets of 3 leaflets but they are smooth and branch off of a much finer stem. The plant crawls along the ground and has a finer more delicate look to it.
  • Trillium spp.: Have sets of 3 leaves but there are no stems to the leaflets.
  • Wild raspberry (Rubus idaeus): Young plants have sets of 3 leaflets and look similar to poison ivy but they have thorns down their stems.
  • Strawberry (Fragaria): Has sets of 3 leaflets.
  • Manitoba Maple aka Box Elder (Acer negundo): Young plants look remarkably like poison ivy and I have misidentified this plant before. Their leaves do not have a shine or sheen to them and the leaves are arranged opposite on the stem, verses poison ivy which is alternate. Their flowers are either gray or bluish.
  • Jack in the pulpit (Arisaema triphyllum): Have sets of 3 leaflets but they have no stems.
  • Honewort (Cryptotaenia canadensis) Has sets of 3 leaflets.
  • Virginia Creeper – (Parthenocissus quinquefolia): is often confused with poison ivy but they have 5 leaflets.
  • Boston ivy (Parthenocissus tricuspidata) have sets of 3 leaflets but they are slightly smaller and more jagged.
  • Poison Oak (Toxicodendron diversilobum): Has sets of 3 leaflets but the fuzzy leaflets have scalloped edges that are more rounded.
  • Fragrant Sumac (Rhus aromatica): Has sets of 3 leaflets that are fragrant (have a lemony smell) and often appear glossy on the upper surface, paler beneath.
  • Toothwort (Lathraea): Has sets of 3 leaflets but they are more jagged.

Where does poison Ivy Grow?

Poison ivy can be found in every province in Canada except Newfoundland (Gov. of Canada 2016), the Canadian territories are also free of it. In America it grows in every state except California, Alaska, and Hawaii (Tec Labs n.d.). It grows in South and Central America, throughout Japan and China and is also found in Bermuda, Bahamas, Australia and New Zealand. It is not found in the U.K or Europe. (Wertz, B. A. 1914).

It grows on almost any kind of soil except peaty soils (Wertz, B. A. 1914). It prefers dry woodlands and thickets and disturbed sites but is also well adept at growing on flood plains, along shore lines, recreational areas, road sides and especially under telephone wires and fence rows where birds perch. In the home setting, yards backing onto or near green spaces may see poison ivy plants spreading into their yards from these adjacent areas. Birds however are likely the greatest source of poison ivy transference into residential areas.

Maps courtesy of U.S. Department of Agriculture
Western poison ivy (left); Eastern poison ivy (right) Distribution maps from the U.S. Department of Agriculture displayed here in accordance with their Policies).

How Does It Spread?

Poison-ivy reproduces primarily from seed that is dispersed by birds when they eat the fruit. It also propagates by leafy shoots sent up from roots and by stems that can take root where they touch the soil.

Symptoms Of A Poison Ivy Reaction

As mentioned in the introduction, skin reactions to the urushiol oil found in poison ivy is actually an allergic reaction known as contact dermatitis. Exposure to the oil, whether it be contact with the plant it’s self or contact with any surface that has any residue of urushiol on it such as pets fur, lawn mowers, shoes, shoe laces, clothing, golf clubs, etc. can cause a skin reaction. It does not take much Urushiol oil to have a reaction. It is so potent that only one nanogram (billionth of a gram) is needed to cause a rash (Gov. of Canada 2016)

Classic symptoms include:

  • Thin red lines. The edges of poison ivy leaves are fairly sharp and can produce fine cuts on the skin.
  • Intense itchiness
  • Rash that may appear within 24 hours to seven days. (Crosbie J. 2020).
  • Swelling
  • Redness
  • Painful blisters
  • Difficulty breathing, if you inhale the smoke from burning poison ivy.
  • gastrointestinal inflammation if ingested.

The severity of your symptoms depend largely on how much urushiol you get on your skin and how sensitive the individual is to the oil. It is quite common for a person who was not sensitive to urushiol oil in the past to suddenly become sensitive to it, as was my case.

Note: The puss from the oozing sores will not spread it to other parts of your body or to others.

What To Do If You Come Into Contact With Poison Ivy

If you are fortunate enough to spot the plant and realize you have made contact the first thing you should do is get out of the sun and heat and wash it off with cool water and soap. The sooner you wash it off the less urushiol you will absorb into your system. Cool water is recommended as hot water opens the pores and increases the spread. If you do not have soap you can use rubbing alcohol diluted with water (1/2 cup to 1/2 cup of water) or vinegar (2 tablespoons in 1 cup of water). Thoroughly clean any surface you may have contacted after touching the plant, using gloved hands. Wash the clothing you are wearing, shoes and shoe laces, gloves, door handles, etc.

If you are experiencing the symptoms but are unaware of where you came in contact with the plant or the urushiol oil then still follow the above steps but you will likely have to broaden your disinfecting area as you will have touched many more objects.

If your reaction is strong visit your doctor who will prescribe a topical corticosteroid cream to apply to the affected skin areas and an anti-inflammatory like prednisone to take orally.

Over the counter remedies include antihistamines like Benadryl or anti inflammatory pain relievers like Advil or Motrin or Aleve. In milder cases oatmeal products or calamine lotion may provide some relief from the itching as will after bite, apple cider vinegar or witch hazel. All in all the symptoms take between 2 and 4 weeks to go away, depending on how bad a case you got. If it is persisting chances are you are being re-infected.

If you have inhaled the smoke from burning poison ivy or ingested this plant you will likely be making a trip to the hospital as the smoke can cause inflammation and painful sores in the lungs and cause them to fill up with fluid. Ingesting this plant can cause painful sores in the gastrointestinal tract.

The amazing thing about urushiol is that it can remain allergenic on clothing for up to 10 years! Crosbie J. 2020

If you are out in the woods hiking or camping with few resources at your disposal there are a few natural remedies that may offer some relief.

  • Burdock or cocklebur (Xanthium strumarium L.) crush the leaves and apply to infected area.
  • Jewelweed (Impatiens capensis) slice the stem, and then rub its juicy inside on exposed parts. This will ease irritation and may prevent an outbreak.
  •  Common Plantain (Plantago major) shred the leaves and apply a poultice to the infected area. This may help to heal poison ivy rash and relieve virtually any skin irritation.

How Can You be Sure Your Reaction Is To Poison Ivy And Not Poison Oak Or Poison Sumac?

Poison oak and poison sumac also produce urushiol. If you did not actually see the plant you will not be able to differentiate the specific plant you brushed up against by the rash it produces, other than perhaps the thin red lines caused by the sharp edges of poison ivy. The reaction and treatment are the same for all three of these plants and thus it really doesn’t matter.

Pacific or western poison oak is found in western North America ranging from Baja California, Mexico, to British Columbia, Canada. Atlantic poison oak (T. pubescens) is native to the southeastern United States (Petruzzello M., Rev. 2017).

Poison Sumac is found primarily in the Eastern Unites States and up into the southern tips of Ontario and Quebec. You’re unlikely to stumble upon poison sumac unless you live around or near a swamp or peat bog (Tec Labs n.d.).

How To Get Rid of Poison Ivy Plants

Before attempting to remove poison ivy plants be sure to wear the proper protective clothing; close-toed shoes or boots, long pants, long sleeved shirt, water proof gloves and ideally face and eye protection. Do not touch your face or any bare skin with your gloved hand. Also try not to touch the surface of anything other than the tools you are working with. When you have finished removing the poison ivy wash your tools and any surface you may have touched. Wash your shoes and shoelaces off and change and wash your clothing.

Cultivation: Poison ivy does not survive cultivation. It can however become a problem in un cultivated areas.

Pull Poison Ivy: In the spring after poison ivy has broken dormancy and while the ground is still very moist pull the plants and their roots.

Cover Area With Black Plastic: Cover the effected area with some heavy black plastic weighted down with some mulch for a year or more.

Caution: Dead poison ivy plants can still cause rashes and must be handled with care, since the urushiol oil can stay active on any surface for up to 5 years. (Gov. of Canada 2016)

Disposal: Black bag poison ivy debris (do NOT compost or brown bag it) and label the bag poisonous plant material. Put it to the curb with your house hold waste. Alternately if you live in the country you can bury dead plants at least 30 cm deep. NEVER BURN POISON IVY!

Chemical Control: Use a systemic herbicide like Glyphosate. This is most effective when the plants are young. Multiple applications may be required due to the extensive underground stems.


Poison ivy does not affect animals or birds but it can produce severe reactions in humans. It grows abundantly in many different types of environments but is especially fond of the edges of dry woodlands and areas where birds like to perch. It’s appearance varies from ground covers to bushes to massive vines that climb to the top of trees; but the leaves always have three pointed leaflets and the stalk on the middle leaf is always longer than the two side leaves. The edges of the leaves typically have a few large teeth (although they may be smooth) and are always arranged alternately up the stems. The stems never have thorns and may have black markings on them; the result of urushiol turning black when it comes in contact with the air. Symptoms may include thin red lines, intense itchiness followed by a rash (often swollen and red). This is followed by painful blisters. If the poison ivy oils get in the lungs there may be difficulty breathing. The severity of one’s reaction to poison ivy can range from no reaction to mild, severe or even death. Learn how to recognize poison ivy for your own safety, then teach your family and friends.

Want to practice your poison ivy identification skills try this poison ivy quiz.

Poisonous to Touch Weeds Covered in This Series Include:

  1. Poison Ivy (Toxicodendron radicans and Toxicodendron Rydbergii)
  2. Giant Hogweed (Heracleum mantegazzianum)
  3. Cow Parsnip (Heracleum maximum)
  4. Wild Parsnip (Pastinaca sativa)
  5. Poison Sumac (Toxicodendron vernix)
  6. Poison Oak (Toxicodendron diversilobum) and (Toxicodendron pubescens)

Other Poisonous to Touch Plants Not Covered in This Series Include:

  1. Poke Weed (Phytolacca decandra): besides being mildly to highly toxic this plant can cause a rash in sensitive individuals.
  2. Stinging Nettle (Urtica dioica): “The leaves and young stems of this herbaceous plant are fitted with stinging hairs tipped with formic acid and other irritants. If touched, these needle-like hairs inject the stinging acid into the skin, triggering a burning, tingling sensation and an itchy rash. Thankfully the symptoms usually do not persist longer than 24 hours” (Petruzzello M. n.d.).
  3. Monkshood (Aconitum napellus): This is a highly toxic plant. The neurotoxins, aconitine and mesaconitine can be absorbed through the skin and cause severe respiratory and cardiac problems. So do not pick or handle this plant without gloves, especially by the root (Monica Wilde M. 2015).
  4. Oleander (Nerium oleander): This is a highly toxic plant. The gummy sap can cause skin irritation or possibly dermatitis in those who are sensitive. If you are growing this plant as an ornamental in your garden be sure to were gloves, long sleeves, long pants, closed shoes and protective eye wear before pruning this plant.
  5. Bloodroot (Sanguinaria canadensis): the flower of this plant produces a reddish toxic sap that looks very similar to blood and contains the toxin sanguinarine. If this sap comes in contact with bare skin it can cause burning. If you get a high concentration of sap on your skin it can even eat away the flesh. If ingested, it is deadly to animals.
  6. Wood Nettle (Laportea canadensis): like stinging nettle have stinging hairs along its stem.

Photo Credits: all photos taken by the author unless otherwise indicated.

References and Resources:

Burtchell J. 2019 (Updated) , Health Line, Retrieved on Jan 31,2021 from: Poison Ivy Rash: Pictures, Remedies, Prevention & More (healthline.com)

Clever Homestead 2013. Poison Ivies: Eastern Poison Ivy and Western Poison Ivy. POISON IVIES: Eastern poison ivy and Western poison ivy | CleverHomestead.com | Create your home, love your home.

Crosbie J. 2020 (updated) D.O.August 5, 2019, Des Moines University, Retieved on Jan. 31, 2021 from: Everything you need to know about poison ivy | News | Des Moines University (dmu.edu)

Gov. of Canada 2016 (modified). Poison Ivy. Retrieved on Jan. 31, 2021 from: https://www.canada.ca/en/health-canada/services/home-garden-safety/poison-ivy.html

Gov. of Quebec 2020 (updated), Retrieved on Jan. 31,2021 from: Identifying and getting rid of poison ivy | Gouvernement du Québec (quebec.ca)

Petruzzello M., Rev. 2017, OA. 2009, Assistant Editor of Plant and Environmental Science, Brittanica-‘Poison Oak’ Retrieved on Feb.1,2021 from: https://www.britannica.com/plant/poison-oak

Petruzzello M. n.d. is Assistant Editor of Plant and Environmental Science. 7 Dangerous Plants You Should Never Touch. Britannica. Retrieved on https://www.britannica.com/list/7-plants-you-cant-even-touch#:~:text=Stinging%20nettle&text=The%20leaves%20and%20young%20stems,sensation%20and%20an%20itchy%20rash.

Rosemary 2014, Your Great Outdoors – Mass Audubon Retrieved on Jan. 31, 2021 from: The Many Faces of Poison Ivy | Your Great Outdoors (massaudubon.org)

Tec Labs n.d., Retrieved on Jan. 31, 2021 from: Where to Find Poison Ivy, Oak & Sumac | Tec Labs (teclabsinc.com)

Wertz, B. A. 1914, Poison Ivy, Pen. State College of Agriculture, Retrieved on Feb. 1, 2021 from: Microsoft Word – POISON IVY.doc (maine.gov)

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