Garden: Least Wanted #1, Poison Ivy

Weeds are something that every gardener has to deal with. My own attitude toward weeds is not as always as hostile as that of the typical gardener. My mom, from whom I learned a lot of what I know about gardening, preferred a garden style that was somewhere between strictly formal, with no plants tolerated out of place, and natural or wildflower, where everything except the most noxious weeds are allowed to grow naturally. Her view tended to be that wildflowers and natural offspring of deliberately cultivated plants were welcome as long as 1) they didn't grow too big or crowd or choke out nearby plants, 2) they didn't look too unattractive or out of place - obviously a subjective judgment, but most garden choices have to be subjective. Taking care of the same garden for my father later, I followed a somewhat similar pattern, except that I err more on the side of giving things a chance to grow. Sometimes this "erring" is costly. Dad mildly but firmly informs me that I need to get more ruthless rather than waiting until halfway through summer to see if those unidentified seedlings of April will turn out to be nice wildflowers, only to discover that they are fast-growing weeds with microscopic flowers that are threatening to devour whole flower beds by the end of June - by which point they have developed clumps of thick roots the size of carrots and need a considerable amount of effort to be removed without tearing out 3 or 4 surrounding plants with them.

In spite of my far too indulgent attitude toward many plants that turn out to be weeds, there are a very few weeds that even I loathe enough to want to eliminate on sight. At the very top of the list is Toxicodendron radicans, better known as poison ivy, the little three-leaved plant growing out of the cracks of the stone wall just beneath a branch from an evergreen shrub here:

It's also known as Rhus radicans, or "The three-leaved spawn of Satan",
though the latter term might just be mine.

This plant is unfortunately familiar to many, perhaps most, people living in the eastern half of the United States and Canada. It's actually not a bad plant in many respects - it is a native plant, its foliage looks reasonably attractive, its berries are eaten by several different species of birds, and it even gets nice red foliage before dropping its leaves in autumn. It has just one slight flaw from a human perspective - all parts of the plant are covered by an oily chemical called urushiol that causes a severe itching and burning rash in the majority of people. Any physical contact between human skin and any part of the plant causes, for most people, anything from a slightly itchy rash to severe swelling and blistering that resembles a fairly serious burn. Some people have no reaction as children, but develop the allergy as adults. Unlike some toxins, the body actually tends to become more sensitive to the oil the more times it is exposed to it. The oil is potent enough that touching objects that have touched the plant, such as clothing and tools, is usually enough to cause a reaction. The WORST thing to do is burn the plant, because this simply vaporizes the oil and can cause severe irritation inside the nasal passages and lungs if one inhales the vapors.

Granted, poison ivy is far from the only plant that can cause a severe and painful reaction for people who simply touch it. Quite a few plants have urushiol - in the United States alone, there are two species of Poison oak and one of Poison sumac that cause similar, or sometimes even more severe effects. Some tropical regions have a number of plants that cause much more severe reactions than poison ivy or its relatives. Different people have different levels of both sensitivity and severity of reaction.

Still, in the northeastern United States, these other plants are non-existent or rare, while poison ivy grows abundantly and lushly in exactly the kind of places where people are likely to encounter it - in gardens, along the edges of yards, along sidewalks and streets, up the sides of trees and shrubs. It's a plant that thrives along the edges of land disturbed by human activity, and therefore many more people will literally come into contact with it than would be the case for a plant that grows mainly in deep woods or swamps. Many of these people will have a reaction that will range from merely irritating to quite painful and even debilitating (though temporary).

Poison ivy usually grows as a vine, either growing up trees, shrubs, rocks, fences, and buildings, or spreading along the ground. Sometimes it will grow more like a shrub. Its most characteristic feature is the leaves in clusters of three, with the middle leaf extended on a petiole (leaf-stalk) while the leaves on either side have little or no leaf-stalk. The leaves typically have a "shiny" and oily appearance, and they are often have a dark reddish hue when they are first emerging:

Growing along the ground with newest growth at upper right.

The stems or vines of poison ivy have just as much oil as the leaves. They are characterized by a distinctly "hairy" appearance when they climb up objects, especially as they get older and thicker:

"Hairy" poison ivy vine growing up chain link fence among other types of vine.
Note the reddish leaves emerging from the upper portions - this was a couple of weeks ago.

Unfortunately the "hairiness" is not nearly as obvious on young vines, and poison ivy also grows along the ground and as a shrub - in which case the stems often have no root hairs at all, since the hairs are used to cling on the objects to support the plant's growth upward.

1 year old stem with some root hairs, but mostly smooth.

There are several other plants that can be confused with poison ivy, especially if you are as paranoid about it as I am.

For example, there's Virginia creeper:

It has five rather than three leaves, but when the plant is growing three leaves sometimes emerge before the other two, making it look very similar to poison ivy. It's not related to poison ivy at all - it's actually a pretty close relative of grapes. In spite of a certain vague resemblance of leaf shape, it is not related to another well-known plant. It's not safe for everyone - it actually produces a different chemical that can cause bad allergic reactions in some people, but for a smaller percentage of the population than poison ivy. I've never had a bad reaction after years of weeding it with bare hands, and I'm really hoping that it stays that way.

Virginia creeper leaves have a similar oily shine to those of poison ivy, and the two plants are both vines that often grow right alongside each other. Below is part of the stone wall between the proper garden and the weed-rich waste area behind it. Poison ivy is growing over the stones toward the left, Virginia creeper toward the right. One branch of the poison ivy extends toward the right and is intermixed with the Virginia creeper. This gives some idea of how one could mix the two up if one is not constantly paying close attention.

Even the bare stems look similar. Compare the Virginia bare creeper vine below with the bare Poison ivy vine earlier in this post.



Another one that can be confused with poison ivy is a very young hickory sapling, which has leaves which are reddish and a little oily looking when they are newly grown. The hickory leaves grow in groups of five, like Virginia creeper, but it's easy to miss the extra two leaves if you aren't looking closely. Unlike poison ivy, hickory tree leaves have fine "teeth" all around the edges, and have a different overall shape:



There are also several types of wild berries, such as blackberries, raspberries, and strawberries, that grow their leaves in groups of three and can look similar to poison ivy. Their leaves tend to have more "teeth" around the edge, though.


So, Poison ivy is my personal most hated weed. When it comes the natural ecosystem as a whole, though, there are plenty that are worse ....