Top 30 Poisonous Flowers and Toxic Plants Every Gardener Should Watch Out For

Some of the most poisonous plants have the most beautiful blooms. We may not regard plants as immediately harmful, but handle, prepare, or eat the wrong one, and you could be in some serious trouble. 

For poisonous plants, toxicity is a pretty neat defense mechanism against being eaten. It ensures their survival long enough to reproduce the next plant and carry on the species. While some deterrents are very obvious – spines, spikes, bright red thorns and a layer of wax, some can appear harmless at first glance. Their defenses are more subtle – the whole plant may be poisonous, or in parts, or it can release a toxin or highly harmful chemical when disturbed.

Most of the plants on this list store poisonous substances for later use. They only turn dangerous as soon as the plant is injured in some way, and the defense mechanism is triggered. Some plants are toxic enough that just brushing one with your bare skin will cause some serious irritation. Others can really ruin your day, and if you’re not careful, can result in death.

The general rule of any plant is that even if you’re ninety-nine percent sure what it is – don’t eat it. Unless you’ve planted it yourself, grown it from seed or bulb, and it’s supposed to be eaten, and you know exactly what it is, and it’s definitely what it looks like, that one percent can cause you a lot of grief, or not. Because you’ll be dead. Most of the plants on this list you wouldn’t dream of eating. Some of them are pretty maintenance-free, so there’s no need to handle them, but let’s be on the safe side!

Below I’ve outlined some of the most common plants you’ll find in gardens which can be poisonous or otherwise harmful. I’ve also gone through some of these plants’ toxic properties, and some of their effects on animals and humans. 

If you suspect someone has eaten a toxic plant or has come into contact with one, don’t hesitate to take them to the emergency room. Best case scenario, it will be nothing, and least they’ll have a clean bill of health. Use the same approach for your pets, as the longer you wait, the more complicated it can get. 

Lily of the Valley

Convallaria majalis, the birth flower of May, is a stunning perennial which is part of the lily family. Unlike most lilies, this is a compact, woodland plant that’s often used as ground cover. It bears another name – glovewort – referring to its early use as a hand salve for chapped hands. 

You can identify this plant by the tiny bells of flowers, usually white or pink in a sea of big, luscious green leaves. The flowers sit on arching or upright stems, flowers pointing to the ground. They often produce red-orange berries once they have finished flowering, and it goes without saying that you shouldn’t eat these!

It’s long-lived and very easy to grow, if you can mimic its natural habitat. Moist soil and lots of shade, and apart from that, it’s pretty undemanding.  It can grow up to twelve inches tall and can spread out, which makes for the perfect plant to fill a bare patch underneath trees and shrubs. It is worth noting though that a lily of the valley is self-sterile, which means that if you’ve taken cuttings of the same plant and planted them together – copies or clones of the original plant – they won’t set seed.

It’s highly poisonous, and all parts of the plant can be toxic. One plant contains roughly thirty-eight cardiac glycosides, which affects the heart and causes it to beat more rapidly, which is true for both humans and animals. As within a lot of nature, what can be poisonous can also be beneficial. These compounds, which are also found in foxgloves, can treat congestive heart failure and an irregular heartbeat, but they have been replaced by synthetic drugs as they’re still toxic. In the past, they’ve been used to coat weapons, and as rat poisons. 

Among an irregular heartbeat, which can easily be fatal, this plant can also cause stomach pain, nausea, blurred vision and a slow and irregular pulse. Always be careful when handling a lily of the valley – if you need to handle it at all. 

Castor Oil Plant

Ricinus communis, the caster oil plant, belongs to the Euphorbiaaceae family, or euphorbias, which have some stunning features. It’s also considered by the book of Guinness World Records as the most poisonous common plant. It’s often grown for its oil, which has a number of uses in the motor industry, and has been historically used in WWI planes and other internal combustion engines. 

A castor oil plant features reddish-green spiky blooms and glossy leaves with lots of teeth. It’s a fast-growing, flowering shrub that can reach three meters tall. The name castor oil potentially derives from the name ‘castoreum’ which is a perfume base made from the glands of a beaver, as it is used as a replacement. It’s also referred to as the palm of Christ, from a popular belief that castor oil can heal wounds. 

Nearly all parts of the castor oil plant are harmful, but the most toxic part is the seeds, which produce ricin when broken. Symptoms usually appear within 2-4 hours of eating the seeds, but they may not appear until 36 hours later. The leaves are also highly dangerous, which can cause neuromuscular disorders when ingested.

Signs of castor oil plant poisoning include a burning sensation in the throat, bloody diarrhea, nausea, a heart rate increase, abdominal pain, and seizures. It’s worth noting that cold-pressed castor oil which is sold commercially is not toxic to humans in normal doses.

Foxglove

Digitalis, or foxgloves, have an unusual, curious appearance, with tall stems and stacked, trumpet-shaped flowers, which come in a kaleidoscope of colors.  They’re a flower favorite of bees and other pollinators, making them immensely useful in attracting wildlife to your garden. They also self-seed like crazy. Depending on the type, they’re either biennial (flowering every other year) or perennials (flowering every year), and can reach up to two meters tall. Providing you don’t touch them, they’re beautiful plants that can add some lengthy color interest to your borders. 

Foxgloves have numerous medicinal uses as well as ornamental, but their unusual appearance can attract the attention of children and pets, so if you have either, steer clear of foxgloves. In particular, the leaves, flowers, and seeds are poisonous. 

Signs of foxglove poisoning include blurred vision, heart and kidney problems, vomiting, and diarrhea. Direct contact with the skin can cause a nasty irritation. 

The good news is that foxgloves don’t require maintenance that means you have to handle the plant. If you want it to flower prolifically, deadhead the old spikes when they’ve finished flowering, but make sure to wear gloves and wash your hands afterward. 

Daffodil

When we think of winter ending, Narcissus or daffodils spring to mind. A symbol of the start of spring and of Easter, we associate them with rebirth and hope. So it may come as a surprise that they’re poisonous, and can make both humans and animals quite ill. 

The bulbs daffodils grow from are similar to onion bulbs, so be careful you don’t mistake one for the other. Daffodil bulbs produce oxalates, and two alkaloids called scillitoxin and lycroine. Eating a daffodil bulb will result in any or all of these: drowsiness, diarrhea, convulsions, vomiting, and contact with the skin can cause irritation.

Daffodils die back after flowering through spring, and it’s important not to cut back the foliage, as the bulbs use these for energy to regrow next year. Daffodils range in appearance, with yellow or white flowers (sometimes a mixture of both) which can occur singly at the end of each stem, or can appear in clusters. You can recognize the newer breeds which deviate from the normal six petals and central trumpet, some have more petals, different shaped trumpets or no trumpets at all. 

Tulips

Tulipa, or tulips, come in a wide variety of appearances, with some mimicking other plants, like peony tulips. They’re widely admired for being easy to grow, and for their breathtaking beauty when they come up every year. They’re often planted in containers to give a beautiful display of color, but they can also be planted in the ground. 

As with daffodils, tulips grow from bulbs which are poisonous, and can be mistaken for an onion. Dogs can often mistake these and can become quite ill. Some signs of tulip poisoning are lethargy, weakness, vomiting, and hypersalivation.

Tulips also contain tulipalin, which causes skin irritation on direct contact. The whole plant contains this allergen, but the bulb has the most concentration.

Oleander

Oleanders are known for their beautiful huge blooms in yellow or pink, and thrive in tropical climates. The Nerium oleander has been so widely planted that no specific region has been established as its origin. It’s also a member of the dogbane family, so keep it away from pets. They can grow from seven to twenty feet tall, and usually grow as a shrub. They can be trained to grow into a small tree with one trunk. The yellow oleander is known as Thevetia peruviana. They are both poisonous, and contain chemicals that affect the heart, including neriifolin, oleandrin, and thevetin A and B. 

The good news is that because this plant tastes bitter, poisoning cases are rare, and the risk of dying from ingesting this plant is relatively low compared to some other plants on this list. 

Signs of oleander ingestion include stomach cramps, an irregular heartbeat, bloody diarrhea, vomiting, and drooling. If you’re unlucky enough to come into contact with the sap, it can cause skin irritation, eye inflammation and rashes.

In animals, signs of ingestion include pupil dilation, rapid breathing, mouth irritation, and can lead to death. If you’re in any doubt, contact your local vet to be safe.

Desert Rose

Adenium obesum, the desert rose, is a slow glowing plant with a thick, succulent stem and gorgeous deep pink flowers. Like the name implies, the bloom shape is similar to a traditional rose. It’s part of the Apocynoideae group of the dogbane family, native to Eastern and South Africa, and Arabia. The leaves arrange in a spiral shape, growing from a thick trunk. 

Traditionally, the sap is used as an arrow poison and a fish toxin. The plant secretes this sap when it has been bruised or broken, which will cause harm to both animals and humans. Animals have also been known to fall ill immediately after just licking the plant! If you have to handle this plant, do so with gloves. Signs of being poisoned by a desert rose include low body temperature, tremors, seizures, dilated pupils, weakness, and mouth sores. 

Where it can’t survive outside, it’s often grown inside in warmer conditions as a houseplant or trained as a bonsai for its lovely ornamental value. It requires lots of sun and regular watering in order to thrive. The flowers appear during the summer months, and it loses both its leaves and flowers when it goes dormant in the winter. 

Angel’s Trumpet (Brugmansia)

The Brugmansia is a real showstopper. Named after the large, fragranced, trumpet-shaped flowers which can grow a foot long, this is a plant you won’t forget. It forms a branching canopy and grows vigorously.  The flowers come in pink, white and yellow, depending on the cultivar. When the plant reaches maturity, it can grow up to fourteen foot high, and spread up to fifteen feet, so this is a plant that wants a lot of room! 

They add a huge ornamental and tropical feel to your garden, and can be grown in containers or indoors if you prefer. It needs lots of water, and a warm, sheltered environment to thrive.

Unfortunately, this plant is on this list, because it’s highly toxic. This can happen very easily by accident, when plant residue enters the bloodstream or stomach. You can easily poison yourself by contaminating your hands, and then rubbing your eyes or not washing your hands before you eat.

Symptoms of brugmansia poisoning in humans include fever, hallucinations, difficulty breathing, memory loss, dry mouth, and confusion. In animals, it can appear as disorientation, rapid behavioral changes, paralysis, slow or fast heartbeat, seizures and loss of appetite. Unfortunately, this plant’s unusual appearance will attract curious animals and children alike, so keep a watchful eye if you’re around the angel trumpet plant. 

Monkshood (Wolf’s Bane)

Aconitum napellus, or more commonly known as monkshood or even wolf’s bane, is grown for its ornamental value and vivid blue flowers. While the name ‘monkshood’ refers to the shape of the flower, the Greek name lycoctonum literally translates to wolf’s bane, which was used to kill wolves with laced arrows or baits. They’re the source of food for many caterpillars and moths, as well as long-tongued bumblebees, so be prepared to see some unusual pollinators if you plant monkshood! It thrives in wet soil which drains quickly, and prefers partial shade. They’re also closely related to delphiniums. 

Monkshood is extremely dangerous, containing alkaloids like aconite and aconitine. You can even be poisoned through broken skin or a cut which comes into contact with the plant. The first signs of monkshood poisoning are usually nausea, vomiting, and diarrhea. Tingling or numbness in limbs can also occur. In more severe cases, visible motor weakness, confusion, dizziness and paralysis in the heart can occur. 

Larkspur (Delphinium)

Delphinium, or larkspur rarely poisons humans. However, it’s to blame for many livestock deaths with its toxicity. While eating any part of a delphinium is a terrible idea, it’s the seeds and younger plants that have the highest toxicity levels. Grown and handled properly, this is a beautiful plant known for its vivid blue flowers, growing atop huge, spiky stems.

You can recognize delphinium poisoning in animals with the following symptoms: sudden falling, colic, drooling, labored breathing, abdominal pain, constipation, and diarrhea. 

Poinsettia

Traditionally grown as a houseplant in the run-up to Christmas, the euphorbia pulcherrima is a lovely plant with usually red or white leaves that resemble flowers. They do come in other colors, but red, white and green are the most common, grown as festive decorations. These plants are not as poisonous as some others on this list. The toxic part comes from the milky sap, which is a trait of the Euphorbiaceae family. This usually results in skin irritation, redness, and a horrible itching sensation. If you’re unlucky enough to eat a poinsettia, you’ll experience vomiting and diarrhea.

Mountain Laurel

Kalmia latifolia is a lovely perennial grown as a shrub or trained as a tree, from the heather or Ericaceae family, and comes from North America. You can recognize them by their gorgeous round pink or white flowers, and glossy evergreen leaves. When an insect lands on the flower, the stamens inside fling the pollen onto the insect. They can grow up to forty feet high! 

Mountain laurels are mainly toxic to animals, and all parts of the plant are toxic. Horses, sheep, cattle, and goats suffer in particular. Symptoms of mountain laurel poisoning include heart irregularity, muscle tremors, rapid breathing, vomiting, and drooling. 

Bleeding Heart

One of the most unusual flowers you’ll find in nature, Lamprocapnos spectabilis is easily recognizable, thanks to the pink heart-shaped flowers with white tips. Native to Siberia, Korea, Japan, and Northern China, this perennial reaches up to four feet in height. Bleeding hearts (see also Bleeding Heart Flower Meaning and Symbolism) prefer moist soil with lots of nutrients, which drains well, and they don’t like full sun if you’re in a hot country. If you live somewhere cooler, they quite like the full sun. If you gently peel back the two outer petals and invert the flower, you’ll see the shape of the white petals, and why it’s also called ‘lady in a bath’. They’ve also been bred to achieve different colors – alba, which is white, ‘valentine’, which is red and white, and ‘gold heart’, which has yellow leaves. 

Bleeding heart plants contain isoquinoline alkaloids, which can cause trouble to humans and animals alike. In humans, it will mostly manifest as skin irritation, diarrhea or vomiting, but it’s much more serious in animals. Dogs in particular will suffer from liver and kidney damage if they eat enough of it. If you see signs of weakness, suddenly lethargy, tremors or seizures or any of these symptoms, even in a mild form, it’s time to get your dog to the vet. 

Hydrangeas

Hydrangeas are firm favorites in many gardens. They’re easy to take care of, and it’s hard to match the bountiful flowers this plant produces all the way from spring through until the first frosts. It can add a lovely sense of structure to any garden, as hydrangeas grow quite tall, and they also make good dried flowers. But there’s always a trade-off. Yes, it’s poisonous. In some people, hydrangeas can cause skin irritation. The buds are also poisonous if ingested. They’re particularly harmful to cats, dogs, horses and children, and the culprit is called glycoside hydrangin. Signs of hydrangea poisoning include nausea, increased heart rate, fatigue, coma, and loss of appetite.

Calla Lily

Like a lot of beautiful flowers, the calla lily or zantedeschia aethiopica is highly poisonous. Recognizable by the lush, arrow-shaped foliage, and small spadix flowers which come in white, green, yellow, pink, and red, these are popular houseplants. Having a poisonous houseplant can be disastrous if you have pets or children, as ingesting it will result in injury, or it can even be fatal. Poisonous or not, always keep your plants out of reach of children, whether they have two legs or four.  

Calla lilies are highly toxic, and most of the plant parts contain calcium oxalate crystals. These are responsible for swelling of the tongue, lips, or throat, stomach pain, burning sensations, and diarrhea.

Baby’s Breath

Often prized as cut flowers or additions to bouquets, Gypsophila or baby’s breath are lovely plants, which come both as annuals and perennials. They hail from the carnation family, and sport tiny white or pink flowers, only growing to a maximum height of 120 cm. 

They’re not the worst plant on this list for toxicity, but that doesn’t mean you can let your guard down. Some people are allergic to the plant full stop. Every part of the plant contains the saponin gyposenin, which causes dermatitis, difficulty breathing, and sinus irritation. 

Pets who eat this plant will suffer from a very upset stomach, and it’s a good idea to take them to a vet if you suspect they’ve eaten baby’s breath.

Amaryllis (Naked Lady Lily)

The gorgeous amaryllis is famed for being an extremely tall lily, which has strong red or white flowers, which often appear when the foliage has died down – hence the lily being ‘naked’ – and have a gorgeous scent. In traditional plant symbolism, amaryllis stands for radiant beauty and determination.  

The plant produces lycorine and other toxic substances, which are harmful to both humans and animals alike. Amaryllis poisoning often presents as body tremors, vomiting, diarrhea, anorexia and excessive drooling. The good news is that the plant apparently tastes pretty bad, so most animals won’t eat a lot of it. If you suspect someone or a pet has been poisoned, seek professional help, even if you’re unsure. 

Iris

Irises are admired across the world for their wildly different blooms, which come in all kinds of colors and heights. They’re perennial bulbs, which don’t like to be buried up the rhizome, as this can stop them from flowering. Often, they have three inner petals which stand upright, and three outer petals which drape downward. Usually, in the middle of the bottom petal, the flower will have stripes of a different color. 

Irises contain quite a few toxic compounds, but the severity of symptoms these cause tend to be quite low. You can recognize iris poisoning by some of its clinical signs – vomiting, diarrhea, stomach pain, and skin irritation.

Water Hemlock

Cicuta, or water hemlock, is a very dangerous perennial. It’s also known as cowbane, or poison parsnip. It grows from two to seven feet tall, and features clusters of small white flowers on long stalks. This makes it easy to mistake for quite a few different plants, some of which are edible, so you should steer clear, just in case. It’s considered to be one of North America’s most poisonous plants. You can find it growing in meadows, along marshes, streams, and other wet areas. 

Both the stem and the leaves contain cicutoxin, which makes it highly poisonous. It causes the brain to become hyperactive, which causes seizures. It also causes convulsions, hypoxia, and sweating, confusion, and dizziness. These symptoms can appear within fifteen minutes. It may take months for them to clear. 

Morning Glory

Ipomea, or morning glory, is a climber which features flowers that open with the sun, though the blooms can be rather short-lived. They come in an abundance of colors, flowering in early summer. Some of the more impressive varieties are “Heavenly Blue,” which are blue with a white throat, “Scarlett O’Hara”, a deep red with a white throat, and “Kniola’s Black Knight”, which are a lovely dark purple with a pink throat. 

Morning glory seeds are particularly harmful, containing lysergic alkaloids that present a similar reaction in the body as LSD, like hallucinations or liver failure. Keep these plants out of reach from children and pets.

Lantana

Lantana camara is a wonderful ornamental shrub, though its growth pattern is very invasive. It grows up to four meters tall. Like hydrangeas, lantanas boast dense clusters of small flowers which come in many colors, and are attractive in any garden. They can also be multi-colored. Lantana attract pollinators with their lovely fragrance, but in domestic settings they can do much more harm than good. 

In humans, symptoms include difficulty breathing, weakness, vomiting, diarrhea, and death.

In animals, signs of lantana poisoning include jaundice, inflamed eyes or mouth, live and kidney failure, appetite loss and frequent urination. 

Clematis

Hugely popular for their wide range of unusual flowers, the perennial clematis belongs to the buttercup family. They’re also known as traveler’s joy, and grow up structures as a flowering vine. 

The culprit responsible for making this plant toxic is a chemical irritant known as glycoside ranunculin, which converts to something called protoanemonin, when leaves are broken or chewed. This causes severe pain if ingested. The plant does contain an irritant which can affect the skin, but this is fairly rare. In any case, it’s best to handle a clematis with gloves. 

Clematis poisoning in humans usually presents as vomiting, diarrhea, and excessive drooling, and comes from eating the plant.

While animals generally won’t chew on a clematis for very long because of the bitter taste, symptoms include vomiting and diarrhea. They usually subside after the animal stops eating the plant, but if you suspect a plant has made your pet unwell, take it to the vet just in case. 

Yarrow

Yarrow, devil’s nettle, or achillea millefolium, is a very useful plant. Traditionally, it was used to staunch bleeding wounds. It can be used to dye wool, and acts as a companion plant in repelling pests from crops. It’s also used to combat soil erosion, and have been utilized for their anti-inflammatory properties. Like any plant, it can be dangerous if used incorrectly. 

They’re fast growing, and feature tiny white or pink flowers atop a long step and feathery foliage. Direct contact with the skin can result in nasty rashes, dermatitis and eczema. Yarrow is also responsible for multiple livestock deaths every year. 

Bloodroot

Bloodroot, sanguinaria canadensis, is a perennial which hails from the eastern part of North America. It boasts large, delicate white flowers which appear in early spring. They’re prized for their ornamental value, though the flowers only last for a couple of days. It’s had a bad reputation, stemming from fake cures for cancer and other ailments, dating back to the 1920s. 

The name ‘bloodroot’ refers to the color of the sap that the roots produce. It’s used as a natural red dye by Native Americans. It’s also very poisonous, and acts as an irritant. Signs of bloodroot poisoning include heart failure, faintness, dizziness, nausea, and vomiting. 

Marigold (Tagetes)

Marigolds are beautiful annuals known for their vivid colors – yellow, gold, orange, or red – and as the perfect companion plant to tomatoes, as they mask the smell of other plants with their own, confusing pests and directing any damage away from crop plants. They’ll bloom for a long time, if you keep deadheading the fading flowers. While you can eat these lovely plants, over-indulging leads to toxicity. The leaves and roots both can be toxic, and have caused dermatitis, eye irritation and blisters.

Peace Lily (Spathiphyllum)

While not true lilies, peace lilies are no less beautiful. They’re known as an air-purifying plant, which absorbs mildew and mold. They’re part of the araceae family, and feature unusual white flowers that form from the leaves. Furthermore, they’re perennials which hail from tropical America, and dramatically droop when they want more water. They’re not nearly as toxic as some plants on this list, but the peace lily’s leave contain calcium oxalate crystals, which make your lips, tongue and throat burn if you eat them. The name comes from the white flowers, which emerge above the green leaves and resemble flags of surrender, or peace.

Peruvian Lily

Alstroemeria or the lily of the Incas, are herbaceous perennial plants which love full sun and well-drained soil. They come in a variety of colors, from a light pink, yellow, red and purple. They also feature spots in the petals in a different color. 

Unfortunately, they’re highly poisonous. Some people grow them as houseplants, in which case extra vigilance is required. The plant contains glycosides, which can cause dermatitis on contact, and poisons both humans and animals. Signs of Peruvian lily poisoning can include eye irritation, blisters, dermatitis, nausea, vomiting and diarrhea. 

Rhododendron

Known for some of the most beautiful flower displays on the planet, rhododendrons are highly prized shrubs. They can have five flowers open from a single bud, which makes for some impressive displays in a wide range of colors. They grow in acidic soil which needs a pH between 5.0 to 5.5, and need good drainage and partial shade, which makes them good plants to have near big trees. Some rhododendrons are evergreen – so their leaves don’t drop during winter, giving some structure to your borders in the barest month, but others are not. 

Rhododendrons contain grayanotoxin, which is harmful to both people and animals. Symptoms usually appear within a few hours, and can include colic, weakness, leg paralysis, a weak heartbeat, diarrhea, and vomiting. 

Buttercup

Do you remember playing with buttercups as a child? Trying to see whether people liked butter, or not? Regardless of the answer, buttercups brighten up anywhere they choose to seed, whether it’s in a patch of lawn or in a border. They’re often considered weeds as they self-seed and are invasive. 

Unfortunately, they’re also highly dangerous. They contain something called glycoside ranunculin, which is present in the plants of the Ranunculus family. This toxin causes excessive drooling, diarrhea, and a reddening of the oral membranes.

Wisteria

Wisteria has been admired all over the world for its unusual, draping clusters of flowers, ranging from pink, purple to white. Some varieties hail from Japan and China, others are native to America. 

Classified as a poisonous ornamental plant, wisteria produces glycoside wisterin, which pets unfortunately like to eat, and throw up as a result. The seeds are particularly nasty for this. Signs of wisteria poisoning in pets include stomach pain, nausea and diarrhea, and you must be careful if you try to grow wisteria as a bonsai, as you’ll need eyes in the back of your head inside your house, as well as worrying about the outside. 

Leave a Comment