A Comprehensive Guide To Hazardous & Poisonous Plants In Therapeutic Settings

Therapeutic horticulture represents the intersection of humanity’s deep-rooted connection to nature and the healing aspects of gardening. Drawing on the tranquility of gardens, it cultivates an environment conducive to physical, psychological, and social growth. By immersing individuals in the natural rhythms of the plant world, therapeutic horticulture nurtures well-being and fosters a renewed sense of purpose. Amidst this lush world of growth and healing, it’s important to bear in mind the reality of hazardous and poisonous plants and that safety must be at the forefront in this work.

hazardous plants and plant safety

The Importance of Plant Safety in Therapeutic Horticulture

An integral part of creating this therapeutic environment is ensuring the garden’s safety. It is not merely about preventing inadvertent brushes with poison ivy or the prick of a thorny rose. It is about safeguarding the sanctity of the garden experience.

This guide will illuminate the lesser-known characteristics of some common plants, explore what you should do if a participant comes into contact with hazardous and poisonous plants and safety tips you should implement in your therapeutic practice.

Table of Contents

hazardous plants and plant safety

Understanding the Risks: Hazardous Plants in the Garden

Identifying Hazardous Plants: From Thorns to Toxins

Beneath the captivating beauty of many plants lie potential dangers. Some produce natural plant toxins, while others sport menacing thorns, dangerous milky saps or allergenic pollen. Identifying hazardous plants correctly is vital to prevent harmful encounters.

The field of therapeutic horticulture necessitates an extensive understanding of its diverse botanical constituents. For instance, the seemingly innocuous Daffodil harbors potentially harmful alkaloids (a group of naturally occurring chemical compounds that are known to have potent pharmacological effects). All parts of the plant are toxic and contact with the skin can cause a severe reaction. 

In the context of horticultural therapy and therapeutic horticulture, the ability to accurately identify these hazardous  plants becomes crucial. It is the responsibility of the horticultural therapy practitioner to be able to discern these dangers amongst the various flora in their care and to educate participants and mitigate risks wherever possible.

Familiar Foes: 12 Common Poisonous Plants in Therapeutic Horticulture Settings

When practicing therapeutic horticulture, you’ll likely come across an array of visually stunning plants. But don’t let their captivating beauty fool you. Many plants, even those common in therapeutic settings, are not as benign as they may seem. Here are examples of 12 hazardous plants you may come across in TH programs, please note this is by no means a conclusive list!

Oleander: This is a beautiful shrub with funnel-shaped flowers that can be white, pink, or red. All parts of Oleander are extremely toxic and can cause severe digestive upset, heart trouble, and even death if ingested.

Foxgloves: They are tall, majestic plants with bell-like flowers that range from purple and pink to white. The leaves of the Foxglove plant are known to contain cardiac glycosides, a group of organic compounds affecting the heart, potentially leading to heart failure if ingested.

Figs: Decorative ficus species, such as weeping fig, contain latex-like proteins in their sap. Therefore, the plants can be a problem for people with latex allergies, who may experience skin or eye irritation, coughing, or other symptoms, either from contact with the sap or through inhalation. Keep in mind that brushing against some figs can also make your skin more sensitive to the sun’s ultraviolet rays, potentially causing burns.

Rhododendrons: These are large, evergreen shrubs with clusters of bell-shaped flowers. Rhododendrons are toxic due to grayanotoxins present, leading to nausea, vomiting, and even coma if ingested in large amounts.

Euphorbia: One of the characteristic features of Euphorbia species is the presence of a milky white sap, or latex, which is often toxic and can cause a range of reactions upon contact, such as skin reactions like redness, itching, and blistering. If it enters the eyes, it can lead to severe discomfort and potential temporary blindness. Ingesting the latex may result in symptoms like nausea, vomiting, and abdominal pain.

Giant Hogweed: Contact with the sap of giant hogweed can cause serious skin and eye irritation, blistering, scarring, and even blindness if the sap gets in the eye. The skin rash may look like a second-degree burn and can leave you with long-lasting scars and sensitivity to sunlight.

Hydrangeas: Known for their large clusters of flowers, Hydrangeas can be a spectrum of colors. They contain cyanogenic glycosides, which can release cyanide when the plant is chewed or digested, causing dizziness, nausea, and potentially fatal respiratory failure.

Poison Ivy: A poison ivy rash typically appears a few days after exposure, and can even take a week or two if this is your first time in contact with the plant. When it does, you’ll know it: You’ll see very red skin, swelling, and blisters, and you’ll feel a serious itch.

Larkspur: Tall plants with spikes of blue, purple, or white flowers, Larkspurs are toxic due to alkaloids that can affect the nervous system, potentially causing paralysis or heart failure.

Baby’s Breath: Baby’s breath (often used in flower arranging) generally isn’t an irritant while it’s still alive, but when it’s dried, it can irritate the eyes, nose, and sinuses, as well as the skin. It can additionally cause asthma in people who touch it frequently.

Lily of the Valley: This plant has small bell-shaped flowers and is highly toxic. It contains cardiac glycosides, which can cause symptoms like nausea, vomiting, slow heart rate, and even heart failure.

Nightshade: This plant bears shiny black berries and bell-shaped flowers. Nightshade’s poisonous qualities come from solanine, which can cause gastrointestinal and neurological disorders, including hallucinations and, in severe cases, death.

Plant Safety: Ensuring a Secure Therapeutic Environment

Basics of Plant Safety: What It Is and Why It Matters

Plant safety focuses on the strategies to minimize risks associated with hazardous plants. It covers areas like correct plant identification, safe handling practices, providing proper signage and immediate response measures for accidental exposure. The importance of plant safety cannot be overstated, as it acts as a strong shield against potential hazards present within the therapeutic garden.

identifying toxic plants

Identification Guide: Spotting the Hazardous Plants

Some plants may subtly hint at their hazardous nature through their physical features. Certain leaf patterns, unusually bright colors, or distinct odors may indicate toxicity. Many of us are familiar with the concept of ‘leaves of three, let them be’, an adage that helps us steer clear of poison ivy. However, not all toxic plants are so easily identifiable and you should always be 100% certain on what a plant is before ever using it in a therapeutic horticulture program. Some of our most dangerous botanical adversaries are masquerading as harmless, even beautiful, additions to our gardens and parks. 

Specificity is key when it comes to identification. Each hazardous plant has unique characteristics that set it apart. The bright, showy flowers of the deadly nightshade, the unique umbrella-like clusters of the poison hemlock, and the glossy leaves of the oleander—each has distinct features that, when recognized, can prevent exposure to their toxic constituents.

While we’ve covered several key markers, remember this is not an exhaustive list, and some hazardous plants may not exhibit any of these common warning signs. A detailed guidebook, mobile application, or online resource, with comprehensive imagery and descriptions, can be indispensable tools for both beginners and seasoned gardeners.

What should you do if an individual comes in contact with a hazardous or toxic plant?

If you come across a toxic plant that is known to you, for example Giant Hogweed, the first thing you want to do is to report it. For example, in British Columbia, you can do this:

Via email:

By telephone:

  • 250.360.3302

In case of contact with a toxic plant, the first step is to identify the nature of exposure – whether it is through skin contact, inhalation, or ingestion. Each scenario necessitates a different response.

During sessions of horticultural therapy, it’s common to encounter various plants. This is why it is so important to only ever work with plants that you know all the potential hazards of in your Therapeutic Horticulture program. However, it’s still good practice to equip yourself with basic first aid skills specific to plant poisoning and to keep essential first aid supplies on hand, such as water, soap, lotion for skin reactions, and contact details of local poison control centers. Ensure that you have a cell phone (with reception) with you at all times in the garden, in case of emergency. 

Professional Plant Removal: When and Why?

At times, the removal of hazardous plants, especially harmful exotic plants or rampant poisonous plants in forests, may be necessary. Professional plant removal services ensure this is done safely and efficiently.

You may consider getting a professional assessment when creating a new therapeutic garden from scratch, ensuring that the garden starts on the right footing, free from any potentially harmful species. Established gardens can benefit from this as well. It is especially relevant when a garden’s flora has grown and evolved over time, with new species potentially entering the mix.

An additional circumstance that might necessitate professional plant removal is when the participants of your therapeutic horticulture sessions have specific sensitivities or allergies. For instance, certain plants might be fine in a general setting but harmful to someone with particular allergies or health conditions. In such scenarios, an expert can suggest safer alternatives that provide similar aesthetic or therapeutic benefits.


Further learning: Intro to Therapeutic Horticulture e-learning course

In June, we launched our self-paced Intro to Therapeutic Horticulture course, designed to provide students with an overview of the principles and practices of horticultural therapy, including the physical, social and psychological benefits of working with plants. If you are interested in further deepening your knowledge and understanding, the course includes advanced lessons on Hazardous Plants and Plant Safety.