Ask the Expert: Dr. Derrick Stowell and Horticultural Therapy

We feature an expert in the mental health and substance use disorder field to answer questions. This issue we talk to Dr. Derrick Stowell of University of Tennessee Gardens about horticultural therapy and it’s benefits for those with substance use disorder, mental health issues and traumatic brain injuries.

Q: How would you describe the people-plant relationship? (Community, social, cultural, etc.)

The people-plant relationship is a complex relationship between humans and plants. It deals with genetics, human history, and survival. Some of the pioneers in describing the people-plant relationship include Dr. Diane Relf, Joel Flagler, Dr. Raymond Poincelot, and Charles Lewis. This relationship goes back to the beginning of time when we as humans were hunters and gatherers. We relied on plants for food, and sometimes protection/hiding from animals trying to rely on us for their food. Research shows that people respond to plants in many ways including lower stress, faster recovery from surgery, preferences for viewing pictures and art that are focused on plants and nature scenes. We also have the deep connection of plants that provide us with food, oxygen, housing, clothing, most of our survival needs. Gardening or horticulture provides opportunities for us to tend and care for plants. In some ways it provides a way for us as people to give back to plants for all they provide us. Plants can survive without humans, but we would not be able to survive without plants. This is both a humbling realization and also one that gives us a very different perspective on this relationship.

Q: What is horticultural therapy? How is it different than a hobby and recreational gardening?

Horticultural therapy as defined by the American Horticultural Therapy Association is the “participation in horticultural activities facilitated by a registered horticultural therapist to achieve specific goals within an established treatment, rehabilitation, or vocational plan. Horticultural therapy is an active process which occurs in the context of an established treatment plan where the process itself is considered the therapeutic activity rather than the end product.”

You may find that people sometimes use the term gardening or fishing is my “therapy.” You even find those on some t-shirts or bumper stickers. Dr. Relf in Chapter 1 of Farming for Health (2006, p. 3) even stated this difference. But it is important to note that the research shows the benefits of nature, plants, and gardening on individuals. The difference is therapy is something that is conducted by a trained therapist. Therapy is prescribed and a form of active treatment for an individual with an illness or injury. My philosophy is that all humans need activities that provide therapeutic outlets to help manage stress and overall health and wellness. When someone gets sick or has an injury, they then may need to seek out medical treatment and that could include horticultural therapy. As a therapist I can help assess and develop goals and objectives to help a person with their overall health and wellbeing goals. My main goal is to then help them regain or maintain functioning and learn to use horticulture as a therapeutic tool once they are discharged from treatment. Some horticultural therapists work in community settings where they provide programs and interventions that promote overall health and well-being.

Q: What is a horticultural therapist, and what settings do they work in?

A horticultural therapist is someone who has become professionally registered by the American Horticultural Therapy Association. The official designation is Horticultural Therapist-Registered (HTR). To become registered, an individual needs to have a minimum of a bachelor’s degree with coursework in horticultural therapy, plant science, and human science. They also need to complete an internship supervised by an HTR. The horticultural therapy course can be found at one of AHTA accredited horticultural therapy certificate programs. An individual needs nine semester credits in horticultural therapy, 12 credits in plant science, and 12 credits in human science. For more details about specific course titles and content you can visit

Q: Please describe what happens on a physiological level when someone interacts with plants.

I am not a neuroscientist. However, there are some basic concepts of how horticultural therapy interacts with plants and the impact on the brain. Some of the basic concepts come from theories such as E.O. Wilson’s Biophilia. Wilson states that humans have an innate connection to living things. That connection is what helps us as humans respond to animals and plants around us. Kaplan and Kaplan’s Attention Restoration Theory illustrates how we respond to prolonged high levels of stress. As we experience stress, our bodies respond through our nervous system. Our body releases hormones including adrenaline and cortisol to help manage the stress. This sets the body up for a fight or flight response. These mechanisms are key to our survival. But the prolonged arousal can cause things like loss of focus on activities, high blood pressure, anxiety, depression to name a few. Being around nature allows our body to recover from stress and helps us to be able to regain focus on difficult tasks. Detweiler et. al (2015) studied the impact of horticultural therapy on cortisol levels. Researchers found that the horticultural therapy program lowered cortisol, which is a common stress hormone. A study by Park et. al (2019) found that a horticultural therapy program showed increased cognitive function in seniors. The results illustrated that presence of brain nerve growth factors may play a role improving brain health from participating horticultural therapy programs.

Q: How can horticultural therapy help someone with substance use disorder, mental illness, and/or a traumatic brain injury?

One element of horticultural therapy is that it should be guided by assessment of each individual and in collaboration with their treatment team. This allows the therapist to develop appropriate goals and objectives for each person. I’ll give a few brief ways that horticultural therapy can improve each of the populations you discussed above.

Substance Use Disorder: Horticultural therapy can provide several benefits to this group. One being that gardening is considered a top leisure pursuit in the United States. So, finding positive outlets for stress and an individual’s leisure time is an important part of the recovery process. Horticultural therapy programs can also provide group experience for individuals to begin to develop positive social interactions with peers. Often when someone has a substance use disorder, they may also have other health challenges such as poor nutrition and physical health challenges. Horticultural therapy can also teach individuals how to grow and care for fruits and vegetable and provide fresh produce at home to help someone regain healthy eating habits. The physical activity related to gardening can also reduce stress, improve physical functioning. After completing a rehabilitation program, an individual may also be interested in giving back. A horticultural therapist could suggest local volunteer opportunities related to horticulture and give individuals an opportunity to help take the skills they learned to provide horticulture, plants, fresh fruits and vegetables to local groups or volunteer at a local community garden.

Mental Health: Horticultural therapy has been shown to help reduce depression, stress, and anxiety. The act of growing and caring for a living thing is a key element in horticultural therapy. Providing opportunities for someone who has a mental health diagnosis to see success in growing plants can have a valuable impact on their self-esteem and help them gain skills to manage stress. The physical components of gardening are considered moderate physical activity by the Centers for Disease Control and Prevention (CDC). The physical activity related to horticultural has the same effect as any other physical activity. This includes improved mental health and better overall health and well-being. It also helps that you may enjoy gardening and plants more than, say running, or working out in the gym.

Traumatic Brain Injury: Those recovering from a traumatic brain injury may need to work on improving stamina and physical strength. Horticultural therapy gives an opportunity for individuals to adapt horticulture activities to everyone’s needs with increasing challenge as treatment progresses. For someone who has a severe traumatic brain injury, challenges such as impulsivity or agitation could be present. Horticultural therapy programs can give an individual the opportunity to practice making choices such as what to plant. Horticultural therapy can also provide space for an individual who is agitated to learn and practice positive coping mechanisms while gardening.

Q: What are some tips for people who want to try this at home to support their own recovery?

You may want to look and see if anyone in your community is a horticultural therapist. Check out what types of programs they offer and consider joining a group and learning more. Growing plants can be done almost anywhere, inside, or outside. So even, if you live in an apartment, you can grow house plants or some microgreens. If you live in an apartment and want to grow more vegetables, look for a local community garden and see what it takes to get your own garden plot. If you are not familiar with gardening, don’t worry. There are many resources such as your local county extension office, public gardens, and garden clubs that have many horticulture experts who love to share what they know about plants. Gardening in general is an exceptional way to help maintain wellness and health. Start small and learn as you go. Don’t worry if you think that you have a “brown or black thumb.” Don’t be afraid to make a mistake along the way. I am always learning and being involved in horticultural therapy or gardening for the therapeutic benefits is a learning opportunity.

Q: What are some additional resources for our readers?

I encourage readers to check out AHTA’s website ( for more information. They are setting up an online search function to find HTRs. This is for consumers looking for a facility or individual who is practicing horticultural therapy so you can find a local resource if you are interested in being involved in a horticultural therapy program. The goal is to have that function running in the next few months. Readers may also want to check out some books if you are interested in being more involved in the profession. Several ones that I utilize in my practice include:

For more information about gardening, check out your local public garden for a list of classes and workshops.

Dr. Derrick Stowell is the Education and Horticultural Therapy Program Administrator for the University of Tennessee Gardens. Dr. Stowell is also an adjunct assistant professor for the University of Tennessee (UT) where teaches the UT’s Horticultural Therapy Certificate Program. He received a bachelor’s degree from Maryville College in Environmental Studies and Outdoor Recreation. He has a master’s degree in Therapeutic Recreation from the University of Tennessee. Dr. Stowell received his PhD from the University of Tennessee in Plant, Soil and Environmental Science. He is a Certified Therapeutic Recreation Specialist (CTRS) and also a Horticultural Therapist-Registered (HTR(). He has received numerous awards including the 2016 American Horticultural Therapy (AHTA) Rhea McCandliss Professional Service Award, and  the 2022 American Horticultural Society’s Horticultural Therapy Award. Dr. Stowell has served on the board of directors for the AHTA and is AHTA’s current Immediate Past President. He spends his time teaching, implementing horticultural therapy programs for a variety of populations, supervising interns, and conducing horticultural therapy research.

If you have a question for the experts, or you are an expert interested in being featured, please email Experts have not been compensated for their advice. We may earn a commission via some of the links on this post – at no cost to you.

Last Updated on November 11, 2022

Leave a Reply

Your email address will not be published. Required fields are marked *