Both Poison Ivy (Toxicodendron radicans) and Poison Hemlock (Conium maculatum) are considered dangerous to humans, especially children. Therefore, it’s recommended to remove the poisonous pair.
Of course, this is much easier said than done. So, as Sun Tzu said: “Know the enemy.”
Characteristics of Poison Ivy
Poison Ivy isn’t technically “poisonous”. Instead, it has a particularly nasty oil called Urushiol, which is found in the leaves, stem and roots. Just brushing against the leaves can deposit the sticky oil on your skin, and a serious rash or blisters will develop very quickly.As the name implies, it has the typical habit of a vine when mature, and sadly, it’s a perennial one. It has hairy, aerial roots to help it attach itself as it climbs, which means older vines can be difficult to dislodge.
It has leaves in groups of three, white berries, and aerial roots that look hairy. It’s also deciduous and its seeds are viable for 5 to 6 years.
Characteristics of Poison Hemlock
Poison Hemlock is a biennial plant and regenerates from seed. In ideal conditions however, it can act more like a perennial. It is also a prolific seeder, but the good news is that the seeds only remain viable for 2 or 3 years.Mature plants look similar to carrots and parsnips, except that hemlock has pointed leaves, purple spots along the stems, and isn’t hairy. They can grow from 3 to 10-feet tall.Poison Hemlock is a notoriously poisonous plant due to the alkaloids present in it, and the entire plant is poisonous if ingested. Poisoning can also occur from contact via open cuts, or via the eyes. In some people, handling hemlock can cause a skin irritation and even a serious rash.
Preparation for Removal
So, how do you eradicate a 6-foot tall poisonous herb? Or a vine that causes blisters on contact? The answer is: very carefully!
The first step is appropriate clothing. Long pants, a long-sleeved shirt, thick gloves (preferably water-proof) and closed shoes.
The next step is to choose your weapons wisely. A long-handled shovel, a rake and a pair of secateurs are my go-to tools. Long handled tools allow you to keep a relatively safe distance from the plants which minimizes contact (and when you’re only 5 foot 6, it certainly helps).If you are dealing with a few scattered plants, then suiting up and digging them out manually is the best option. This is easier when the soil is moist, and best done before any seeds appear.
Make sure you remove everything (leaves, stems and roots) and don’t put them in the compost. Put them in a bag and throw them in the regular trash.
Removal of Poison Ivy
It’s possible to cut the vine at the base and leave the upper part of the plant to die off – just be careful when you eventually remove it, since even dead plants contain urushiol and will still cause a rash.
Now for the roots. You can either dig them out, or you can out-compete the ivy by maintaining a thick, short lawn. Another option for the roots is smothering (read below for details).
In most cases, only humans are irritated by the plant, and many animals, including domesticated ones such as goats and rabbits eat it, especially the young shoots. You can even hire a goat. But don’t touch any animal that has been in contact with poison ivy since the oil will be present on their fur.
Removal of Poison Hemlock
For tall plants, I minimize contact by chopping off the top of the plant with either my shovel or secateurs first, leaving about a foot at the base to help with digging out the tap roots (or read below about smothering).
For scattered plants, once the mature plants are completely removed (don’t forget to dig up that pesky tap root), then it’s usually just a matter of re-visiting the site and keeping a sharp eye open for the juvenile plants for the next 2 or 3 years.
Thankfully the seed dispersal is low, so it’s unlikely to be very far from where you dug up the parent plant. The juvenile plants are much easier to remove with a weeding tool, and you can spray very young seedlings with a vinegar solution.
Decrease the PH and Increase the Shade
Poison Hemlock has a hard time establishing in acidic soils, especially under heavy shade. Ideally you want to keep soil disturbance to a minimum, so once the adult plants have been removed, try planting an acid loving perennial and dropping the pH by watering it in with a vinegar solution. Avoid any of the solution touching the leaves.
The drop in the pH may last for a month or up to a year; depending on the soil type and rainfall, so a cheap pH meter is always a great investment.
The hemlock moth (Agonopterix alstroemeriana) is the only insect that can help with controlling large infestations of poison hemlock. The downside is that they can be expensive to buy, but for around $100 you can have a crew of tiny employees doing the hard work for you.
Smothering Method for Poison Ivy and Poison Hemlock
One low cost method that can be utilized for any weed is smothering. Lawn clippings, wood chips, straw, gravel or even other weeds can be used. Anything to stop the sunlight from germinating the seeds or stimulating re-growth.Some hints to maximize the effectiveness of smothering are:
- Remove as much of the weed as possible first. The less leaves it has, the less chance it has to keep growing. A weed eater (especially one with a blade) can be an efficient way to do this, just make sure you wear a full-face mask and eye protection.
- A few sheets of overlapping newspaper or cardboard should be laid down first, with the smothering materials over the top.
- Completely cover the infested area. Too much is better than not enough.
- Make sure the smothering layer is at least 4 inches at all times. The layer will settle and start breaking down, so aim for 6 inches when initially laying down a smothering layer.
- Keep the area smothered for as long as the seeds remain viable.
How Not to Remove Poison Ivy and Poison Hemlock
It is not recommended to burn either of these poisonous plants. The toxins in the plant are released into the smoke and inhalation can cause severe respiratory problems.
Household vinegar solutions desiccate the leaves of all plants, but it has almost no effect on established roots. Hence why it won’t actually kill mature plants. For this reason, a vinegar solution will only be effective at killing very young seedlings that don’t have established roots.
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