How to Identify Poison Ivy

The best way to avoid problems with poison ivy is to learn to identify it. Since poison ivy in present in a vast portion of North America, it's likely you'll run it to it at some point if you live in areas it grows or if you travel to any. grow almos There are only three things that are absolutely true about poison ivy identification: (Note that the following criteria applies to poison ivy but not necessarily poison oak or sumac.)

1. Poison ivy always has 3 leaves

Poison ivy never has more than 3 leaves on each stem. If you see 5 leaves, 7 leaves or any number higher than 3, you're not looking at poison ivy (however, you could be looking at poison oak, which is also harmful).

If you see a group of 3 leaves on a vine but also see a group of 5 or more leaves on the same vine, then that can't be poison ivy. You're most likely looking at Virginia Creeper instead. Occasionally a poison ivy leaflet drops off and you'll have 2 in a bunch, but never more than 3.

Getting technical: The correct way to describe poison ivy is to say each poison ivy leaf consists of 3 leaflets. The picture at the right shows one poison ivy leaf (circled in orange). That leaf consists of 3 leaflets. Whether you call them leaves or leaflets, just remember there are always 3.

2. Poison ivy does not have thorns

Raspberries, blackberries, and other bramble-type plants look very similar to poison ivy because they have 3 leaflets and even may have leaf "notches" like poison ivy can have, but they have thorns on the stems. Poison ivy stems are either smooth or hairy, but never thorny.

The picture to the right is NOT poison ivy because the stem is thorny. I believe this is a wild raspberry bush since I saw others in the vicinity that were bearing fruit.

Click the photo to see a larger version that clearly shows the thorns. In the full size photo, look in the lower right corner... that IS poison ivy hidden in with the raspberry bush. Look out for that sort of thing because poison ivy frequently grows intermixed with other plants!

3. Poison ivy leaves are arranged alternately on the stem

"Alternately" means each leaf or group of leaflets doesn't grow right across from each other and usually alternate sides of the stem (in other words, as you're looking at the plant, one set of leaflets might be on the left side, the next set of leaflets on the right, the next on the left, etc.). The poison ivy picture on the right shows alternate leafing well. Click on the photo to see a larger version.

The other type of leaf arrangement is called "opposite". Leaves that are arranged opposite from each other are right across the stem from each other. Young Box Elder trees are often mistaken for poison ivy, however, Box Elder leaves are opposite. Poison ivy leaves are never opposite - they are always alternate.

The diagram below shows more about the difference between alternate and opposite leaf arrangement:

Alternate Leaf Pattern: Alternate leaves only have a single leaf (or group of leaflets) attached at one location on a stem, often the leaves alternate from one side to the other as they go along the stem or they may be in a spiral pattern. Poison has three leaflets occurring alternately on the stem.

Opposite Leaf Pattern : Opposite leaves refer to two leaves being attached at the same location on a stem, but opposite each other on either side of the stem. Box elder and young maple trees have opposite leaves.


Uncertain Identification Criteria

Now that we've learned the three hard and fast rules, here is other popular criteria for poison ivy identification. However, you can't completely count on these things to ALWAYS be true, so don't ever count on them exclusively.


Poison Ivy Habitat

Poison Ivy can grow practically anywhere. It can be in deep woods to full sun fields to the beach. It grows on telephone poles, signs, fences and trees, or it can be a free-standing plant or bush. It has no soil preferences and can grow in anything from dry, sandy, clay-filled soil to dark, rich soil. It often creeps along the ground. So long as there's some kind of soil, sunlight and water, it will grow.

It is not limited to wild areas, either. Poison ivy is fond of gardens and fence lines in your yard. It likes to grow against the house or garage or inside of your bushes and hedges. It will be hidden in with your other plants.

About the only place poison ivy usually does not grow (at least not for very long) is in mowed lawns. That's because mowers cut off the leaves. Poison ivy needs its leaves to make food through photosynthesis. Without food, it will die.

This is why you almost never see it growing in the middle of a lawn. However, if you only weed whack a fence every couple weeks, poison ivy can move right in.


Totally off the wall: I worked as an environmental educator for 5 years and had at least one live, potted poison ivy plant in my office for show and tell. It had a nice sunny window in my office, so it had light and water... really all it needed. However, keeping the plants taught me two things: it does not like to live in pots and it does not like to be overwatered. I managed to kill (unintentionally) every plant I had. So, there's your solution: pot it and overwater it. You'll kill it, guaranteed.

How to Kill Poison Ivy

An almost guaranteed way to kill ivy off in the yard is to use a spectrum herbicide. However, be careful, because it will kill everything, not just the ivy.

I'm not a fan of chemicals at all, so I prefer to go with a different method: put vinegar on the leaves and the sun will help kill it off. However, you usually have to do that more than once to be effective. Again - be careful because vinegar will also kill everything else it touches. I conductied an experiment with this method and had good results.

Of course, you can't and shouldn't carry weed killer on a photo shoot. Even if you used it, it would not work instantaneously. A better idea is to just learn to avoid poison ivy.

By the way, NEVER burn poison ivy plants or vines! The urushiol oil can spread in the wind, get into your lungs (or someone else's), and cause a very severe reaction.


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