By Dr. Mercola
Most poisonous plants are invasive weeds, including poison ivy, oak, sumac and the plant recently discovered in Virginia — giant hogweed. Giant hogweed is on the federal noxious weed list, which means it is unlawful to propagate, sell or transport it across state lines as it is invasive and often crowds out native plants.
While poison ivy, oak and sumac often are hidden among other low-lying bushes or found growing up trees, giant hogweed, which can reach a height of 10 to 15 feet, is a striking and dangerous plant. While each of these poisonous garden plants can cause varying degrees of skin rashes and burns, giant hogweed sometimes causes long-lasting or permanent damage.1
Poison ivy, oak and sumac are closely related and often found in similar environments. All three grow throughout the U.S., except Hawaii, Alaska and parts of Nevada.2 While irritating and uncomfortable, the rashes are not usually dangerous unless the oil is aerosolized from burning the plants. Inhaling fumes may trigger an allergic reaction in your lungs. However, there are natural ways to rid your yard of these invasive plants without resorting to chemicals or fire.
The rashes from poison ivy, oak and sumac can be unbearably itchy if left untreated. While your primary care physician may want to prescribe a corticosteroid, there are much safer treatments you may begin at home without multiple side effects.
Although steroids are commonly prescribed for a number of different conditions, the medications are linked with significant side effects, including fluid retention, elevated blood pressure, osteoporosis, mood swings and an increased risk of infection.3 In other words, these are drugs you likely want to steer clear of as much as possible.
Learning to recognize each of these invasive plants (as prevention is the best medicine), ways of preventing rashes and burns from poison plants even after you've been exposed, and the treatments you can use at home to alleviate the symptoms will help you enjoy more of the outdoors.
History of the Hogweed
Giant hogweed (Heracleum mantegazzianum) is a member of the carrot and parsley family of plants and native to Caucasus Mountains on the border of Europe and Asia.4 The plant was originally introduced to Great Britain as an ornamental due its unique size and impressive flowers. Originally named after the mythical god Hercules, it was then imported to the U.S. and Canada as an ornamental plant in Victorian gardens.5
The size of the flowers made the plant a favorite with beekeepers as the plant provided a substantial amount of nectar. Presently, the plant is established in New England and along the Mid-Atlantic and the Pacific Northwest6 regions of the U.S. The plants can be found growing along streams and rivers, forests and roadsides.7 It prefers abundant light and moist soil, and the size of the plant ensures those growing under it are choked out.
A powder was made from the dried seeds and used as a spice in Iranian cooking.8 As with so many invasive plants, the giant hogweed escaped cultivation. In addition to being on the federal noxious weed list, several states have also listed the plant on a list of prohibited plant species. Hogweed is a perennial, living three to five years, with tuberous root stalks. It survives between growing seasons, enduring dormancy during the winter months.9
Large white flowers form at the top of the plant and are flat-topped and umbrella-shaped, often measuring 2.5 feet across. Horticulturist describe the flowers as resembling “Queen Anne's Lace on steroids.”10 The plant produces seeds in the late summer that may remain viable in the soil for up to 10 years.
Toxins of Hogweed Increase Sun Sensitivity
While striking and producing beautiful flowers, the plant also produces a toxic sap, which when in contact with the skin and combined with sunlight, can cause severe irritation, burns and blisters. This phytophotodermatitis is caused by photosensitizing furanocoumarins11 making the skin photosensitive and unable to protect itself from sunlight. This may cause third-degree burns, affecting layers of the skin down to the dermis.
The plant’s watery sap contains furanocoumarins, a psoralen. The photo toxic effects occur when psoralen binds to nuclear DNA under the influence of ultraviolet radiation and causes the death of affected cells.12 This irritation may worsen when the skin is moist from sweat or there is dew on the plant.
The reaction may start as quickly as 15 minutes after exposure, although it often takes 48 hours for blisters to form. These blisters may become pigmented and scab over, taking weeks to heal. The scars left from hogweed burns can last for months or even years. Once exposed to hogweed sap, the skin can remain photosensitive for several years.13 If the sap gets into your eyes it can cause photosensitivity of the cornea and result in temporary or permanent blindness.
Identifying Giant Hogweed
As impressive as this plant may be, it is often mistaken for other invasive weeds and plants in the carrot and parsnip family. You can see pictures of the impressive leaf span and flowers of the giant hogweed in this short video. The plant may grow up to 15 feet in height with stems 1 to 3 inches in diameter. The stem of the giant hogweed has inconsistently placed dark purplish spots. The stems may also be covered with hairs but not as prominently as on the leaf stalks. Some of the plants confused with the giant hogweed include:14
- Cow parsnip: The cow parsnip resembles giant hogweed closely, but grows only 5 to 8 feet tall.
- Angelica: This plant may be differentiated by smooth, green to purple stems without bristles and nodules. The flowers seldom reach 1 foot across and the plant is much shorter, gaining no more than 8 feet in height.
- Poison hemlock: This plant is a non-native biennial, also shorter than giant hogweed and growing only up to 9 feet in height. Although the stem has purple blotches, the stems and stalks are smooth and hairless.
- Wild parsnip: This plant also causes phytophotodermatitis but without the severity of giant hogweed. It seldom gets taller than 5 feet and the stems have vertical grooves running along the length.
For a positive identification, take pictures of the entire plant and send them to your local county Extension office.15 They can help identify the plant and give assistance with removal and control in the following years. It's important you take strong precautions before attempting to remove this plant and that you always wear appropriate protective gear.
Identify Common Garden Poison Plants and Prevent Rashes
There’s a reason it’s difficult to identify poison plants in your garden — they can vary based on the season, species and area of the country they are growing in. As shown in the short video, poison ivy and oak can have a different appearance in different locations, and can grow as a vine or shrub. Poison ivy, oak and sumac are also found in different areas of distribution throughout the United States and Canada.16
While the Eastern species of poison ivy is located mainly on the East Coast and Central Midwest area of the U.S., Western poison ivy is found throughout the West, Canada, East Coast and much of the Midwest. Pacific poison oak is found along the western U.S. and the West Coast of Canada, while Atlantic poison oak is found along the southern east coast and Southern States of the U.S. Poison sumac is found predominantly on the east coast Canada, the U.S. and Texas.
Avoiding these plants is the best way of preventing the rash, blisters and itching that accompanies exposure to the oil coating the poison leaves. The old saying, “Leaves of three, let it be,”17 is a good rule of thumb for identifying poison ivy. The leaf shape, color and variety may change, but the arrangement doesn't. Look for stems with a large leaf on the end and two slightly smaller ones flanking it.
Poison oak leaves also cluster in sets of three, with the edges of solid green leaves white, reminiscent of an oak tree.18 However, poison sumac has leaf stems containing seven to 13 leaflets with one growing from the end of the stem and the others paired opposite each other. Leaves may have black or brownish black spots filled with urushiol, the oil triggering the contact dermatitis, rash and blistering.
Recognizing the plant may help prevent exposure, but sometimes it happens anyway. Retired biomedical scientist Jim Brauker explains that by understanding the science of how urushiol oil affects your skin, it may be possible to get poison ivy on your skin, be allergic and still not get a rash.19 He explains a method not requiring any special products or treatments, but instead using friction and consistency.
Since the urushiol takes a couple hours to soak into the skin, by washing it off the exposed parts of your body, you can avoid a serious poison ivy rash altogether. However, getting the oil off isn't as easy as it sounds. The molecule, similar to engine grease, sticks to your skin and spreads rapidly.20
Brauker recommends scrubbing thoroughly with flannel or a washcloth, rinsing and repeating three times to get rid of all of the oil. This process does not apply to urushiol coming in contact with sensitive skin under the eye or in cuts. In these cases, the urushiol is likely to penetrate much more quickly.
Symptoms of Poison Ivy, Oak and Sumac Exposure
In most cases, the symptoms associated with poison plants, such as ivy, oak or sumac, include a red rash within a few days of contact, swelling, itching and streaking or weeping blisters.21 The fluid from these blisters is not contagious. Instead it is the urushiol causing the skin reaction. Therefore, after coming in from an exposure, it is important to take off all your clothing and wash it immediately, as well as any garden equipment you may have been using.
The contact dermatitis is the result of the reaction of urushiol to your skin. The oil is found on the flowers, stem, leaves and roots of the plant and it takes very little oil to cause a reaction. Unfortunately, the oil remains active in the plant long after the plant has died.22 After the oil is absorbed and metabolized, your immune cells recognize it as a foreign substance and send out cytokines and white blood cells. During this process some of your normal tissue is damaged, resulting in the symptoms you experience.
In some cases, you may not react with the first or second exposure, leading you to believe you're not allergic and won't get a rash. However, increasingly people have the allergic reaction with repeated exposure. If the plants are burned and you inhale the fumes you may and experience difficulty breathing. This requires immediate emergency care. Lesions on your skin can continue to appear for up to two weeks. It may also be necessary to see your physician if:23
The reaction on your skin is severe or widespread |
Your skin continues to swell over several days |
Your blisters begin oozing pus |
You have a fever greater than 100 F (37.8 C) |
The rash doesn’t improve significantly, or get better, within a few weeks |
The rash affects the area on or around your eyes, genitals or mouth |
Treatment After Exposure to Poison Garden Plants
After exposure to giant hogweed, it's important to cover your skin from exposure to the sun and get indoors where you can wash your skin with soap and cold water as soon as possible. It is important to keep it covered anytime you are outside and to stay out of the sun for three to four days to reduce your skin reaction and potential burning.24 If a reaction does occur, this area may remain very sensitive to sunlight for several years, so it may be important to keep the area covered from the sun when possible.
Following exposure to poison ivy, oak or sumac, it's important to wash the urushiol off your skin with soap and water, using friction from a washcloth. If you do experience an outbreak, for the most part you may be able to treat it at home using natural products to reduce the swelling, itching and pain without resorting to over-the-counter medications or prescription corticosteroids. Try a combination of the following to address each of the different symptoms.
While untreated poison ivy often resolves spontaneously within two to three weeks, the following suggestions may help your body to heal faster and relieve the pain and itching resulting from the contact dermatitis.25,26,27
• Itching and inflammation: Cold compresses or soaking the area in a lukewarm oatmeal bath may help reduce the inflammation and soothe your skin. Consider using oatmeal in a container accommodating the entire area or take an oatmeal bath. Filter the water as it leaves the tub or pour the fluid down the garbage disposal from a small basin used to soak an area of your body, so it doesn’t clog your drain.
Baking soda in a lukewarm bath is recommended by the American Academy of Dermatology to soothe the skin and reduce the inflammation.28 The inside of a banana peel or watermelon rind may also help reduce the itch from the rash. Calamine lotion or capsaicin cream may help to reduce itching.
Dairy products, such as buttermilk or yogurt applied to your skin (unless you have a dairy allergy) may help draw the fluid from your blisters. Soak in the tub with tepid water for 20 minutes with 12 chamomile tea bags to reduce the itchiness and uncomfortable feelings on your skin. Consider brewing the tea or dark-brewed coffee and dab it on your rash with a cotton ball every few hours.
• Do NOT scratch: The rash is very itchy, but you must refrain from scratching as much as possible. Bacteria under your nails may trigger a skin infection and scratching increases the damage to your skin and the potential for scarring. If the blisters from the rash do break open, leave them alone and covered to prevent infection.
• Reduce the reaction: A paste of bentonite clay and water covering the area where you first notice the contact dermatitis may reduce the reaction your skin experiences, and therefore your symptoms. Bentonite is a natural clay found at your local health food store.
• Speed healing: Soak a paper bag in apple cider vinegar and lay it across the rash. If you cool the apple cider vinegar first it will also help to reduce the itch as the vinegar helps to speed healing of the rash.
• Cool the burning: One of the symptoms of contact dermatitis from poison ivy is a burning sensation over the rash area. The gel from an aloe vera plant may help to cool the burn from the rash in much the same way it helps soothe a sunburn.
Control Poison Garden Plants Naturally
Using a safe and effective method to kill the plants in your yard without resorting to chemicals helps reduce damage to the environment and your exposure to poison as well. No matter what method you use to remove plants, it’s essential to cover your skin with long pants, long shirt and gloves.29 The extra minutes you spend preparing may save you days of itching and burning. Duct tape your pants around your socks and your shirt around your gloves, and make sure your gloves don’t have any holes.
Giant hogweeds are tough plants and difficult to eradicate from your garden, but not impossible. Never touch the weed with your bare skin and don’t touch your gloves covered in sap with your bare skin. Natural manual or mechanical methods include cutting the roots and removing the entire plant.
Manual control does not cause immediate death and you'll need two or three treatments each year for several years to deplete the root reserves and ultimately kill the plant. Cutting the roots is ideal for a single plant or small infestation. Plants having flowers heads should be cut before seeds have matured to prevent spreading.
Do not mow plants if they're larger than your mower and never mow them if there's a flower or a seed head attached to the plant. Another option is to cut the plants to the ground and cover with soil and plastic or landscape fabric with mulch on top. Check this each year to ensure seedlings do not get through and then add vegetation. The New York State Department of Environmental Conservation30 has a resource page describing each of these methods in detail.
The fastest way to get rid of poison ivy, oak or sumac is to dig them up, ensuring you get at least 8 inches deep into the soil to remove as much of the root system as possible.31 Disposal of the plants you dig up is another important factor to reduce the spread of the oil. Do not compost, shred or burn the plants as this causes the oil to spread. Instead, bag the plants and roots in plastic and dispose of them in the garbage.
Once the plants are removed, cover the area with cardboard or mulch to help prevent regrowth of the plants. Watch the area around the cardboard for tiny plants growing up from roots you may have missed. If suiting up and digging up the plants isn’t your style consider a nontoxic solution of 1 cup of salt, 1 gallon of water and 1 tablespoon of dish soap.32
Mix this solution thoroughly and pour it into a sprayer. Use the stream setting on the sprayer if the plant is close to other plants you would like to save, as this formulation will kill all plant growth.
Once you’re done treating or pulling poison plants, you will want to strip off the clothes you’re wearing, being careful you don’t touch the outside of the clothes with your bare hands. You may want to have a friend remove your gloves while they are wearing disposable vinyl gloves.