29 Common Garden Plants That Are Poisonous

Plants are an important factor in the lives of all humans for one reason or another. They provide food and clean the air we breathe. For those of us who garden, they provide countless hours of personal enjoyment. But what about the plants that have harmful effects on humans?

Many of the common things we grow in our gardens are poisonous, and it’s important to ID and handle them safely. Things we grow in our gardens sometimes contain toxins that are harmful to the human body. Even coming in contact with the sap of some plants can be dangerous. Ingesting others could be fatal.

There are groups of plants that you can safely assume are toxic. Many flowering bulbs, for example, contain poisonous compounds. These compounds tend to be most concentrated in the bulbs themselves. Anything with the word poison in the name we can assume is poisonous, as well. Deadly Nightshade tells us all we need to know right there in the name. 

There are plenty of plants that fly under the radar, though, and these are potentially the most dangerous. If we know what to avoid, obviously, it’s easier to protect ourselves from those things that are a danger. Let’s talk about some common plants in our gardens that house hidden and not-so-hidden dangers. You will find many of these in local nurseries and may even have them in your own garden. 

Oleander

Botanical Name: Nerium oleander

• Plant Type: Evergreen shrub
• Hardiness Zones: 8-10
• Poisonous Parts: All

This attractive plant is one that most southern gardeners are familiar with. It is a shrubby evergreen that produces large, beautiful clusters of flowers. It’s also extremely poisonous. All parts of the plant are toxic.

Sometimes, even coming in contact with the leaves can cause skin irritation. Oleander contains cardiac glycosides, which can affect the heart and ultimately prove fatal. Steer clear of this plant if you have curious animals or small children that visit your garden. 

Foxglove

Botanical Name: Digitalis purpurea

• Plant Type: Herbaceous annual, perennial, or biennial
• Hardiness Zones: 4-9
• Poisonous Parts: All

Foxgloves are beauties in the garden. Their tall, stately stems and bell-shaped blooms beckon to bumblebees. They are easy to grow and also highly poisonous to humans and animals. All parts of a foxglove are toxic, and ingestion can result in a host of negative effects. Digestive pain, vision problems, and general weakness are all common side effects. The greatest danger is to the heart. Foxgloves contain digitalis glycoside, which can slow or stop the heart. 

Hydrangea

Botanical Name: Hydrangea macrophylla

• Plant Type: Perennial shrub
• Hardiness Zones: 3-9
• Poisonous Parts: Bark, flowers, leaves, stems

It’s hard to believe that a plant as popular as a bigleaf hydrangea could be harmful. All parts of hydrangea contain hydracyanosides, well-known toxins. The most harmful parts are the flowers and leaves.

Ingesting portions of the plant can cause severe digestive upset. While only considered moderately toxic to humans, ingestion of a large amount could prove fatal to a child or small animal. 

Lily-of-the-Valley

Botanical Name: Convallaria majalis

• Plant Type: Rhizomatous perennial
• Hardiness Zones: 3-7
• Poisonous Parts: All, especially roots and seeds

Lily-of-the-valley is a lovely flowering perennial that symbolizes happiness, purity, and youth. It’s also highly poisonous. All parts of lily-of-the-valley contain cardiac glycosides and saponins, which adversely affect the heart. However, there’s only a risk when large amounts of the plant are consumed. 

The seeds are especially toxic. Eating as few as one to five seeds can cause cardiac arrhythmia. Another consideration: these are often grown as cut flowers. The water left over from these flowers will also be poisonous. 

Calla Lily

Botanical Name: Zantedeschia

• Plant Type: Bulbous perennial
• Hardiness Zones: 7-10
• Poisonous Parts: All

The beautiful calla lily is another common entry on the ‘Do Not Eat’ list. Not that you were considering, but this one contains calcium oxalate crystals. This makes eating any part intensely painful, like eating tiny shards of glass! If swallowed, these crystals will continue on through the digestive tract wreaking havoc. 

Though it is rare for any serious or fatal effects to result, I wouldn’t take a chance. Make sure to give adequate warning to children and keep this one away from pets. 

Castor Bean

Botanical Name: Ricinus communis

• Plant Type: Perennial or annual shrub
• Hardiness Zones: 9-11
• Poisonous Parts: Flowers, leaves, sap, and especially seeds

Castor bean is an attractive and exotic-looking shrub that makes a nice addition to the landscape. Unfortunately, all parts of the shrub, but especially the seeds, are extremely poisonous. Castor seed oil is a common ingredient in beauty products, but the oil doesn’t contain the toxic compound.

Ricin is the dangerous toxin contained in castor bean, and it is 12,000 times more poisonous than rattlesnake venom, by volume! I would probably not plant this in my garden, but if it’s there, and you don’t want to remove it, exercise caution when tending to it. A few seeds are enough to kill an adult.

Angel’s Trumpet

Botanical Name: Brugmansia spp.

• Plant Type: Perennial shrub or small tree
• Hardiness Zones: 7-10
• Poisonous Parts: Flowers, leaves, seeds

For such a beautiful specimen, an angel’s trumpet certainly can cause a lot of trouble. The flowers, leaves, and seeds of the plant are poisonous, containing dangerous compounds such as hyoscyamine, scopolamine, and atropine.

These alkaloids can cause paralysis, tachycardia, hallucinations, and death. The plant no longer exists in the wild, so you’ll only encounter this one in gardens. It’s stunning, but keep your distance and wear gloves when pruning and handling seeds. 

Hyacinth

Botanical Name: Hyacinthus orientalis

• Plant Type: Bulbous perennial
• Hardiness Zones: 4-8
• Poisonous Parts: All parts, primarily the bulbs

Hyacinths smell heavenly. Between their visual appeal, potent fragrance, and cool season habit, these are very popular spring flowers. Like many bulbous perennials, however, they are toxic to humans and animals. The entire plant contains some alkaloid compounds and calcium oxalate crystals. The highest concentration is in the bulb. 

Eating these can cause extreme oral and digestive pain, and they can be an allergen. This one is rarely fatal to humans but can be to small animals. Utilize gardening gloves when planting them to avoid contact dermatitis. 

Dumb Canes

Botanical Name: Dieffenbachia seguine

• Plant Type: Herbaceous perennial
• Hardiness Zones: 10-12
• Poisonous Parts: Leaves, roots, sap, stems

Dieffenbachia is a common tropical garden and houseplant. It has large, tropical leaves with striking variegation and thrives in indirect light. It contains the same compounds as many others on this list.

Ingesting parts of the plant can may cause oral and digestive issues. Even more concerning, it may cause swelling of the mouth and airways. It is rarely fatal to humans, but causes severe discomfort. It can be fatal to small animals by way of asphyxiation.

Narcissus

Botanical Name: Narcissus spp.

• Plant Type: Bulbous perennial
• Hardiness Zones: 4-8
• Poisonous Parts: Flowers, leaves, roots, stems

This genus of plants includes daffodils, and all parts of this common spring flower contain a chemical called lycorine. Research this chemical, and you’re likely to find plenty of studies lauding its positive effects. Outside a controlled medical environment, there is a toxic element in narcissus plants, especially when consumed in large amounts. The chemical contained can cause nausea, vomiting, and other digestive troubles. 

The highest concentration of lycorine lies in the bulbs of the narcissus plant. Ingesting these is rarely fatal, but it’s not worth the risk. Additionally, the sap can cause skin irritation, so handle the flowers with care. 

Larkspur

Botanical Name: Delphinium

• Plant Type: herbaceous annual or perennial
• Hardiness Zones: 3-9
• Poisonous Parts: Flowers, leaves, seeds, stems

As a pet owner and a parent, this is one that I steer clear of. It makes a wonderful addition to the cutting garden but sadly, is highly poisonous. Larkspur, or delphinium, are pretty, flowering perennials sometimes grown as annuals. These plants contain several mixtures of alkaloids that are toxic to humans and animals.

The chemicals are present in larger amounts in new growth and seeds. Young specimens tend to be more dangerous than mature ones. The side effects are numerous, with the most severe being paralysis and death. There is no cure for larkspur poisoning.

Iris

Botanical Name: Iris spp. 

• Plant Type: Bulbous perennials
• Hardiness Zones: 5-9
• Poisonous Parts: Roots, sap, seeds

Just like many other spring flowers that come from bulbs, irises are not for eating. Irises, and in particular, their roots and bulbs, contain noxious compounds. These aptly named compounds include irisin, irisine, and iridin. 

Ingesting this plant can lead to pain and burning in the mouth, throat, and abdomen. Vomiting and diarrhea are other common maladies brought on by eating parts of the iris plant. Contact with various parts of the plant can also cause dermatitis. Ingesting is not likely to be fatal, but it will be highly uncomfortable. 

Bleeding Heart

Botanical Name: Dicentra spp.

• Plant Type: Herbaceous perennial
• Hardiness Zones: 3-8
• Poisonous Parts: All

Bleeding hearts are easy to care for, and their flowers are unique and beautiful. This entry is highly pest and disease-resistant. One thing it is not is edible. Compounds in the plant can cause skin irritation after contact, but that’s not the worst of it. All parts of this plant, and especially the leaves, contain dangerous alkaloids. 

Eating this plant has some serious side effects. Mild interactions can involve sedative, narcotic, and spasmodic effects. In more serious cases, ingestion can cause serious damage to kidney function and heart arrhythmia. 

Monkshood

Botanical Name: Aconitum

• Plant Type: Herbaceous perennial
• Hardiness Zones: 3-7
• Poisonous Parts: All, especially roots and seeds

Monkshood goes by many names. It has lovely purple flowers and a delicate appearance, in spite of its relative adaptability. This cultivar prefers moist soil and full sun but grows fine in partial shade, too. Growing it isn’t an issue, but ingesting it is. The entire plant, but especially the seeds and roots, are poisonous. 

An extract from the plant, Aconitum lycoctonum is used in herbal medicines. Other types contain aconitine and other alkoloids. Consuming these can cause stomach and mouth pain, irregular heartbeat, and breathing issues. The feeling of creeping on the skin, as though one is covered in insects, is also noted. 

Autumn Crocus

Botanical Name: Colchicum autumnale

• Plant Type: Bulbous perennial
• Hardiness Zones: 4-9
• Poisonous Parts: All

All types of crocus can be poisonous, but autumn crocus is particularly dangerous. This plant isn’t a true crocus but bears a strong resemblance. Autumn crocus contains an alkaloid called colchicine. The progression of poisoning from this perennial includes gastrointestinal problems, followed by life-threatening complications. These can include liver or kidney failure, heart failure, as well as respiratory distress. 

The effects of this plant are very dangerous for anyone already suffering from specific ailments. Those with kidney, liver, or heart diseases are highly vulnerable to any exposure. 

Wisteria

Botanical Name: Wisteria spp.

• Plant Type: Woody perennial vine
• Hardiness Zones: 5-9
• Poisonous Parts: Seeds and seed pods

I have a special place in my heart for wisteria. It’s just such a wonderfully nostalgic vine with the most lovely growth habit. It’s also, you guessed it… poisonous. The seeds develop inside delightful, velvety seed pods, both of which are highly toxic. Even the wood can be troublesome if eaten. 

The seeds and pods of the plant contain the chemicals lectin and wisterin. It’s highly unlikely to ingest a lethal amount of wisteria, especially for humans. However, you will end up with a burning mouth and a very upset stomach. 

Daphne

Botanical Name: Daphne mezereum

• Plant Type: Deciduous or evergreen shrub
• Hardiness Zones: 4-7
• Poisonous Parts: Bark, fruits, leaves, sap

We’re not talking about a Bridgerton here, although the beauty of this sweet-smelling plant does justice to The Diamond of season one. Unlike our favorite Duchess, the daphne plant is highly toxic. All parts contain the compounds daphnin and mezerin, with the highest amounts contained in the berries. 

Daphne wears the label of severely toxic. Some lesser symptoms of poisoning are thirst, vomiting, and swelling of the lips and tongue. On the more severe end of the symptom spectrum are internal bleeding, difficulty swallowing, and coma. I’m not saying don’t grow it, but plant it where children and pets can’t access it. 

Rhododendron

Botanical Name: Rhododendron spp.

• Plant Type: Evergreen or deciduous shrub
• Hardiness Zones: 4-8
• Poisonous Parts: All, especially leaves

Rhododendron is a large genus of plants that also includes azaleas. These deciduous and evergreen shrubs are absolutely stunning in the spring with their large clusters of sizable blooms. These plants contain toxic resins called grayanotoxins, with a high concentration found in the leaves. 

These toxic resins can cause some seriously negative health effects. Gastrointestinal irritation is the least of these effects. Eating too much of this shrub can cause kidney and liver damage, hemorrhage, and secondary aspiration pneumonia. Honey from bees that feed on these plants is often found to contain concentrations of toxins. 

Night Blooming Jasmine

Botanical Name: Cestrum nocturnum

• Plant Type: Evergreen shrub
• Hardiness Zones: 9-11
• Poisonous Parts: All, especially sap and berries

Night-blooming jasmine is said to have aphrodisiac properties. It could be the tauntingly heady fragrance that floats across a summer evening breeze. Or, it could be the elevated temperature and rapid pulse brought on by the chemicals atropine and solanine contained in the plant. 

All parts of night-blooming jasmine are toxic, but the berries and sap are the most dangerous. This one may look and smell sweet and innocent, but its history is anything but. There have been fatal poisonings in children and animals. The sweet scent can even cause dizziness and breathing difficulties. 

Yew

Botanical Name: Taxus spp.

• Plant Type: Evergreen shrub or tree
• Hardiness Zones: 4-8
• Poisonous Parts: Bark, fruit, leaves, especially the seeds

Yews are attractive and interesting evergreens. They add texture and interest to the garden all year. They produce bright red berries which mature in the summer. The only non-poisonous part of the entire plant is the flesh of these berries. 

Don’t start prepping to make jam just yet, the seeds are the most toxic part of the plant. The toxic alkaloid taxine, contained in the plant, causes some serious health effects, including death by cardiac arrest. 

Cherry

Botanical Name: Prunus spp.

• Plant Type: Deciduous tree
• Hardiness Zones: 5-9
• Poisonous Parts: Leaves, bark, and pits of fruit

Here’s a common tree in the garden that might surprise you with how toxic it is. I’m calling this one cherry, but it encompasses all the trees in the Prunus genus. Plums, peaches, nectarines, and apricots fall into this group. 

The leaves, bark, and pits are toxic. They contain cyanogenic glycosides. If that sounds familiar, it should. It breaks down into cyanide! Don’t chew or ingest the seeds or any other part of these trees. Digestion and chewing can release the poison. If you have livestock, plant your trees in an area where they can’t access them. 

Lantana

Botanical Name: Lantana camara

• Plant Type: Perennial shrub
• Hardiness Zones: 7-11
• Poisonous Parts: Flowers, fruits, leaves, and sap

Butterflies love lantana for its abundance of nectar. It may be a treat for pollinators, but lantana is poisonous to humans and livestock. It is most dangerous in large amounts, so cows and other grazing animals tend to be more affected than humans. Even smaller amounts can cause various unpleasant effects, including gastrointestinal upset.  

Mountain Laurel

Botanical Name: Kalmia latifolia

• Plant Type: Evergreen shrub or tree
• Hardiness Zones: 4-9
• Poisonous Parts: All

Touted as a beautiful, shade-tolerant, flowering evergreen, there is a darker side to mountain laurel. Yes, the shrub is very pretty, with broad evergreen foliage and clusters of sweet, pink flowers. However, it is extremely poisonous. It’s so poisonous that honey made from these flowers is toxic, too! 

All parts of the plant contain grayanotoxins, which are diterpene compounds. The symptoms are complex and extensive. Nearly all functions of the body can experience complications after ingestion. Consuming as little as 0.2% of a human or animal’s body weight can be fatal. 

Sago Palm

Botanical Name: Cycas revoluta

• Plant Type: Tropical evergreen
• Hardiness Zones: 9-12
• Poisonous Parts: All, especially seeds

Sago palms are a popular landscaping element in warm-climate gardens. They have statement-making form and their adaptability makes them almost too easy to take care of. Most folks know that these palms are poisonous to pets. They are also very toxic to humans. 

The seeds contain the most toxic compounds and are the easiest to consume, which is why pet owners should beware. You should also be very careful when pruning this tree, as all parts are toxic. Side effects can be less serious like gastrointestinal discomfort or skin irritation. Advanced side effects include liver and neurological issues. Half of all ingestion cases are fatal.

Gloriosa Lily

Botanical Name: Gloriosa superba

• Plant Type: Herbaceous tuberous perennial vine
• Hardiness Zones: 8-12
• Poisonous Parts: All, especially tubers

Gloriosa lily is related to autumn crocus, and similarly, it is pretty but poisonous. This tropical vine is popular for its brightly colored flowers. Like all other plants in the Colchicaceae family, all parts of the gloriosa lily are toxic. They contain a toxic alkaloid named for the family, colchicine. 

The tubers contain the highest concentration of the alkaloid, making them the most dangerous. Eating the plant, and especially the roots, can be fatal. 

Morning Glory

Botanical Name: Ipomoea alba

• Plant Type: Annual vine
• Hardiness Zones: 10-12
• Poisonous Parts: Seeds

Morning glories are often mentioned when poisonous plants are the topic. They do have some toxic properties, but it’s not as troublesome as some sources may indicate. Eating the flowers and leaves of the morning glory is not harmful, except that they can be a choking hazard. The real danger is in the seeds.

Morning glory seeds contain an alkaloid that is similar to lysergic acid diethylamide (LSD). Ingesting these seeds can cause gastrointestinal upset, but more concerning, hallucinations. Keep kids away from this vine.

English Ivy

Botanical Name: Hedera helix

• Plant Type: Evergreen perennial vine
• Hardiness Zones: 4-13
• Poisonous Parts: All

We’ve all heard of, and probably encountered the wrath of poison ivy. That’s not the only type of ivy to worry about. English ivy, which is a very common landscape element, is also toxic to humans. This plant has attractive foliage and a classic vibe. Just don’t eat it, or let it grow on the side of your house. It will do damage to your house and your body.

The sap of the vine can cause skin irritation in humans. If consumed in significant amounts, English ivy can cause dangerous effects in humans and animals. The foliage is much more toxic than the other parts of the plant, so keep curious pets and children away. 

Nicotiana

Botanical Name: Nicotiana spp.

• Plant Type: Flowering annual or perennial
• Hardiness Zones: 2-10
• Poisonous Parts: All

We all ought to know by now that tobacco is not healthy for humans. Did you know that it’s not just dangerous to smoke the dried leaves? All parts of the nicotiana plant are potentially toxic to humans. These annuals and perennials are often used as ornamentals. They have pretty, pleasant-smelling flowers and are easy to grow. 

On the downside, certain species of these plants contain nicotinic alkaloids. These alkaloids can have widely varying effects on the body, determined by their concentration and length of exposure. Less severe reactions include abdominal pain and hypertension, among others. More severe reactions include coma and respiratory failure. This refers specifically to N. glauca, N. tabacum, and N. x sanderi. 

Honeysuckle

Botanical Name: Lonicera spp.

• Plant Type: Perennial vine
• Hardiness Zones: 4-9
• Poisonous Parts: Berries

This last vine is likely to be a surprise. How many of us grew up plucking the flowers from this vine to suck out the sweet sap at the base of the bloom? Well, we were probably safe, as the flowers are edible, but this is not true of the entire plant. 

Honeysuckle berries and the seeds they contain are poisonous to humans. Though their effects are not often fatal, ingesting the seeds of this plant will cause digestive discomfort, including severe diarrhea. Most parts of the plant contain saponins, which are something akin to soap. They can also cause issues with blood clotting.