2026 Conference Speakers

The 2026 AHTA Conference Presenters

Speaker Bios

Andy Ziegler, MD

Andy Zeiger is a resident physician in pediatrics at Columbia University. He received his M.D. from Thomas Jefferson University and B.S. in Molecular, Cellular, and Developmental Biology from the University of Washington. He has written six AHTA Magazine articles and presented on horticultural therapy topics to many audiences, including the AHTA Growing Impact campaign, Philadelphia Flower Show, and numerous medical school and residency settings. His research explores the integration of horticulture into pediatric care. Andy has published 13 peer-revied scientific works and presented at national meetings of the American Thoracic Society, American Horticultural Therapy Association and the Aerospace Medical Association.

Antoinette Vasseur, CNIP, CPD

Antoinette Vasseur, CNIP, CPD, is the Therapeutic Nature Program Manager at ClearView Communities in Frederick, MD, where she designs and facilitates nature-based therapeutic programs for adults in mental health treatment. She is a Certified Nature Informed Practitioner and holds an Advanced Certification in Permaculture Design. Antoinette is the creator of InnerRoots™, an inner-ecosystem framework that weaves permaculture principles with therapeutic nature practices to support self-awareness, nervous system regulation, reflection, and inner growth through relationship with the natural world.

Arushi Sinha, PhD

Dr. Arushi Sinha is a medical anthropologist and communications leader with extensive expertise in scientific publishing. Her leadership skills bridge the gap between clinical evidence and impactful communication, ensuring excellence across diverse therapeutic landscapes, including mental health, neurology, and oncology. By leveraging a deep understanding of the publishing lifecycle, Dr. Sinha translates complex data into meaningful narratives. She has mentored the next generation of healthcare professionals, fostering a human-centric approach to medical evidence, melding therapeutic innovation with evidence-based rigor.

Binxia Xue, HTR, PhD

XUE Binxia, Ph.D., is a research fellow in the School of Architecture and Design, Harbin Institute of Technology. He is also a member of the Key Laboratory of Cold Region Urban and Rural Human Settlement Environment Science and Technology，Ministry of Industry and Information Technology, and the Horticultural Therapist-Registered, HTR. The research direction is healthy living environment and natural healing system.

Calliope Correia, HTR, M.Sc. 

Calliope Correia is a Registered Horticultural Therapist based in Fresno, California. With more than eight years at Land Together, she began as Program Manager at Avenal State Prison, where she supported participants in transforming a small piece of toxic land into a thriving ecosystem. Her work is rooted in therapeutic horticulture and strengthens connection—to community, to self, and to the land. Now Regional Lead for Southern California and the Central Valley, Calliope oversees six correctional facility programs, including both California women’s institutions. She is passionate about cultivating relationships and expanding equitable access to therapeutic services that foster meaningful, lasting change.

Colleen Griffin, HTR

Colleen Griffin, HTR has worked as a contracted provider in private practice since 2018. She is a graduate of the Horticultural Therapy Institute (HTI) and holds a BS in Public Health from the University of Maine. In 2022 she joined the faculty at HTI, where she teaches Fundamentals and Management courses. Colleen co-owns Cultivating Well-Being, LLC, a therapeutic horticulture practice focused on community wellness and environmental stewardship. She is an active member of the American Horticultural Therapy Association and a master gardener volunteer through the University of Maine Cooperative Extension.

Collie Turner, THP

Collie Turner, THP, is the Founder and Executive Director of Heroic Gardens, a nationally recognized nonprofit advancing community-based therapeutic horticulture for U.S. Veterans. Since 2018, the organization has introduced more than 4,900 Veterans and their families to the healing power of plants and nature through innovative therapeutic horticulture programs. Heroic Gardens has received the Outstanding Programming Award from the Mid-Atlantic Horticultural Therapy Network and a national Commendation from the U.S. Department of Veterans Affairs for its Mission: Windowsill program—one of only five programs recognized in partnership with the VA. Collie holds a Certificate in Horticultural Therapy from Temple University and regularly speaks about grassroots leadership, community health, and nature-based healing.

Leah Diehl, HTM, RLA

Elizabeth (Leah) Diehl, RLA, HTM is Director of Therapeutic Horticulture and Lecturer in the Horticultural Sciences Department at the University of Florida (UF) and is a landscape architect, master gardener, and horticultural therapist. She developed and manages the Certificate in Horticultural Therapy at UF, conducts research, and runs therapeutic horticulture programming for diverse populations. In partnership with UF Health departments and clinics, Leah has published papers exploring therapeutic horticulture on student mental health, low back pain, psychiatric inpatients, women with cancer, adults with end-stage kidney disease, and also on the benefits of nature in human health.

Faryn Hart. LCSW, HTR

Faryn is a Registered Horticultural Therapist (HTR) and Licensed Clinical Social Worker (LCSW) who has volunteered at San Quentin State Prison with Land Together since 2016. Faryn currently works as a Child and Family Therapist in Richmond, CA with families who have experienced significant challenges including separation, discrimination, and system engagement. Prior to this work, they facilitated horticultural therapy programming in residential eating disorder treatment as well as with a non-profit in San Francisco, Homeless Prenatal Program, working with families experiencing financial and housing insecurity.

Gayle Gratop, HTR

Gayle Gratop, HTR, is the Family, Consumer, and Health Sciences Agent for the University of Arizona Coconino Cooperative Extension in Flagstaff. Her career with Extension began in 2019, and since 2022, she has partnered with community organizations and local school districts to provide horticultural therapy/therapeutic horticulture programs for at-risk youth. Her educational background includes degrees in environmental studies, horticulture, and agricultural education. She is a 2021 graduate of the Horticultural Therapy Institute and is currently working on a PhD in Interdisciplinary Health where her research investigates stressors, coping, and mental health needs for women in Arizona agriculture. 

Gunjan Koul

Gunjan Koul is the Founder and Executive Director of Seed & Bloom, a nonprofit bringing therapeutic horticulture, culinary arts, and nature-based activities into prisons in New Mexico. She holds a certificate in Horticultural Therapy from the New York Botanical Garden and draws on her background in education, gardening, and restorative programming to create spaces centered on healing, creativity, and connection. Her work includes partnerships with initiatives such as the GreenHouse Project at Rikers Island and the Conservation in Prisons Project. Through gardens, kitchens, and learning environments, Gunjan believes in the power of plants, shared experiences, and joy to foster growth.

Hsiang-Hua Chen, MS, HTR w THTA

Hsiang-Hua (Melanie) Chen is a horticultural therapist (HTR with Taiwan Horticultural Therapy Association) with a background in psychology and neuroscience. Her work focuses on supporting wellbeing through horticultural therapy and nature-based activities. She provides therapeutic sessions and programs for diverse populations, including older adults and individuals with different needs, etc. Through her practice, she integrates knowledge of the mind and brain with the restorative qualities of plants and horticultural/gardening activities. She is also interested in small-scale practice-based research to better understand the therapeutic effects of horticultural activities.

Isa Pena

Isa is a beekeeper, urban farmer, and program manager with Land Together living on Coast Miwok land in the Bay Area, CA. isa facilitates therapeutic in-prison garden programming and leads outdoor leadership programs for youth with incarcerated loved ones. isa completed their Permaculture Design Certificate in 2022 through Soul Flower Farm’s ROOTS program, is a Soul Fire Farm’s FIRE Immersion program alum and is currently pursuing certification as a horticultural therapist through the AHTA and as master beekeeper through UC Davis’s California Master Beekeeper Program. 

Jeanne Schultz, HTR

I’ve been involved in the Horticultural Therapy field since 2020. I earned a certificate in HT from HTI and became a registered therapist shortly after. I apply my background in education and as a Peer Support Specialist - Addictive Disease, while working with several nonprofit organizations in the Atlanta area. I’m excited to have a part in this year’s conference and to be a member of the AHTA Board of Directors. 

Jennifer Smith-Sims, HTR

Jennifer Smith-Simms is a dedicated professional with over 34 years of experience in the horticulture field, and she has been an integral part of the Missouri Botanical Garden for the past 24 years. In her role as Public Programs Manager, she oversees various educational initiatives including Adult and Youth & Family Education, Scout Programs, and Therapeutic Horticulture within the Education Division. Holding a B.S. in Plant and Soil Science with a focus on Therapeutic Garden Design. Jennifer has been a registered horticultural therapist with the American Horticultural Therapy Association since 2004.

John Pilat

John Pilat is an Engineer, father and artist whose lifelong connection to nature led him to explore horticultural therapy and its healing potential. After 15 years supporting Veterans, John discovered Heroic Gardens and quickly realized it offered both a community and pathway to personal wellness. Through working alongside licensed therapists and particapating in therapeutic horticulture programs, John has learned science based healing techniques while supporting other Veterans on similar journeys. Time in the garden has strengthed his well being and expanded his creative expression. When not gardening, John enjoys cooking for his children and creating unique artistic pieces that reflect his love of nature.

Katie Andrews

Katie has been working in Social and Therapeutic Horticulture (STH) for five years. She trained at Thrive, the Society for Horticultural Therapy, gaining the STH Diploma with distinction and the John Weighman Prize for Excellence. Katie works at the Ridgeline Trust, a therapeutic garden in Reading, UK with mixed needs groups and people experiencing mental ill health. She also works in community settings running STH sessions focusing on improving wellbeing. Before this, Katie was an RHS trained gardener and also ran her children's school garden project. Her earlier career was spent working in communications.

Kayte Kitchen

Kayte is the Coordinator of the Therapeutic Garden Program at the Royal Children’s Hospital in Melbourne, where she enhances the well-being of patients, staff, and caregivers through nature-based experiences. With over 25 years of experience in education and counselling, she combines her horticultural expertise with therapeutic practices to foster healing and emotional resilience. Through her work, she aims to facilitate personal growth and well-being for patients and their families, showcasing the transformative power of nature therapy. Kayte also runs her own private practice, Admirari Nature Therapy where she conducts individual and group sessions that emphasize sensory experiences and nature immersion. These sessions help participants reconnect with the natural world through reflective activities that promote emotional regulation and mindfulness.

Lana Dreyfuss, LPCC, SEP, HTR

Lana is a licensed professional clinical counselor, somatic experiencing practitioner and horticultural therapist registered. She/they holds a Masters from the University of Maryland in counseling. Currently working at United Indian Health Services in Northern California, living gratefully on Tolowa Dee-Ni land and serving Native American community members providing behavioral health services to include the modality of horticultural therapy. Lana has been serving on the AHTA Board of Directors since 2004, currently serving as Secretary. Lana leads the Credentialing Work Team of AHTA promoting the credentialing of horticultural therapists to raise the standards of the profession. Lana is grateful to Revolution AMC, Professional Testing Corporation and to countless individuals who have helped create this historic moment for AHTA through participating in the Job Task Analysis, Item writing for the exam, and Exam development tasks. 

Lara Fahnstock

Lara Fahnestock has first-hand experience with the healing power of nature and gardens. In her role as Director of Therapeutic Gardens, she can share this passion with others. Lara oversees DUG’s therapeutic gardens from the initial build and planting to training the onsite staff and working directly with participants. Lara is a 2024 graduate of the Horticultural Therapy Institute, has a Biology/ Pre-Med degree from Colorado College, is a Licensed Massage Therapist specializing in trauma-informed care, and holds leadership certificates from the Naropa Institute and the Alexander Association.

Marisol Clarke, HTR

Marisol works as a Horticultural Therapist for Skyland Trail. She enjoys connecting adult and adolescent clients who struggle with mental health to all aspects of the natural world. She is a firm believer to just get outside and be present as a first step to healing. Marisol enjoys working creatively and connecting weekly HT lessons to other disciplines like culture, language, math, science, and writing. When not working, Marisol runs a small goat farm with her husband and son that provides nature-based events and spaces for respite for the local community.

Matthew J. Wichrowski, MSW, HTR

Matthew J. Wichrowski MSW, HTR has been practicing horticultural therapy at Rusk Rehabilitation NYU-Langone Medical Center for over 30 years and is currently Clinical Associate Professor of Rehabilitation Medicine. He teaches in the Therapeutic Horticulture Certificate Program at New York Botanical Garden, presents regularly at national and international conferences, and has won many awards for his work. Matt is also Editor-in-Chief of the AHTA’s Journal of Therapeutic Horticulture. His research interests center around the effects of nature on human health and wellness and his work has been published in a variety of media. 

Meghan McKieran

Meghan Mckiernan, BS, HTR currently serves as the 

Manager of the Therapeutic Gardens Program at Legacy Health, Located in Portland, OR. Meghan has been in this role since August of 2020 and has been working in therapeutic gardens since 2015. Meghan is a graduate of the horticultural therapy degree program from Colorado State University. As a registered horticultural therapist, 

she calls upon an extensive, broad-based background to facilitate interdisciplinary garden design teams and to develop therapeutic programs for patients, visitors, and employees. The focus of her training is on gerontology, pediatrics, in-patient rehabilitation, horticulture, and fund developments/ donor-relations. Her work focuses on gardens in healthcare, horticultural therapy for a wide variety of populations, health benefits of gardening and nearby nature, therapeutic garden design, and HT internship supervision. 

Paul Mallory

Paul Mallory (he/him) first joined the Seed and Bloom team in March of 2025. His role has since expanded to Program Manager as he now helps facilitate in each of the different programs that Seed and Bloom offers. Paul joined the team because he is passionate in his belief that everyone in his community deserves the opportunity to live with dignity and joy, and he loves that Seed and Bloom strives to offer just that. He is excited by the power food has to connect people, whether it is through growing food, cooking, or sitting down and enjoying a meal together.

Rebecca Reimer

Rebecca Reimer is an educator and horticultural therapy practitioner passionate about helping people build resilience through plants, gardens, and hands-on learning. Her work uses horticulture to create meaningful spaces where students and participants can grow in confidence, responsibility, emotional regulation, and connection. Rooted in the belief that growth often happens through challenge, Rebecca sees the garden as a powerful place to practice perseverance, hope, and healing. Through school-based gardening and community projects, she helps others discover that, like plants in a grove, people can be supported, strengthened, and equipped to thrive together.

Seth Lemons, DNP, BS, APRN, AGACNP-BC, CCRN-CMC

Seth Lemons DNP, BS, APRN, AGACNP-BC, CCRN-CMC was an intensive care nurse for 8+ years in rural Southern Ohio before transitioning to his current role as a critical care nurse practitioner fellow at The Ohio State University. He is professionally interested in the utilization of nature-based interventions in healthcare settings to promote patient and employee physical and emotional health and wellness. In conjunction with his Doctoral of Nursing Practice education at OSU, Seth completed a Horticultural Therapy Certificate Program through the University of Tennessee-Knoxville, and directed a hospital-based therapeutic gardening program to reduce stress and burnout in ICU employees. 

Dr. Shakiba Ghasemi Assl, MD

Shakiba Ghasemi Assl is a postdoctoral researcher at UCSF’s Center for Health and Nature. She studies how people use technology to connect with nature and how these experiences can support healing and mental well-being. With a background in medicine and global health, she brings a human-centered perspective to research on nature and health.

Sol Mercado

Sol MercSol is a Reentry Coordinator at Planting Justice, an organization based in Oakland. Sol spent 16 years in prison out of a 31-year sentence and was released 5 years ago. Since her release, Sol has become a passionate advocate and freedom fighter, using her voice to advocate for those still incarcerated. One of Sol’s most meaningful contributions is her work building healing gardens inside prisons. These gardens serve as living memorials to victims of crime and as spaces for healing, reflection, and growth. Through nature, Sol teaches incarcerated individuals the power of restoration—both of the land and of the self. 

Stephanie Ramirez, LCSW, THP

Stephanie Ramirez, LCSW, is a psychotherapist with over nine years of experience providing trauma-informed care and supporting programs that serve diverse communities. Her work spans individuals with severe mental illness, developmental disabilities, military populations, and those who have experienced complex trauma. She brings a collaborative, client-centered approach to care and leadership, helping cultivate compassionate teams and inclusive services. Stephanie focuses on integrating holistic modalities, including horticultural therapy and expressive arts, into mental health treatment. She is passionate about how nature-based practices help people take root, grow through adversity, and bloom into more connected, resilient versions of themselves.

Teresia Hazen, MEd, HTR, QMHP

Teresia Hazen served for thirty years as coordinator and leader of Legacy Health's therapeutic garden program across twelve gardens in the Portland, Oregon, metro region's six-hospital system. In addition to being a registered horticultural therapist (HTR), she holds a Master of Education degree (MEd) and a K – 12 Public School Administrative Credential. She is a Qualified Mental Health Professional (QMHP). The focus of her training is on child development, gerontology, addictions counseling, special education, horticulture, and curriculum design. Teresia draws on her broad, extensive background to facilitate interdisciplinary garden design teams and develop therapeutic programs in healthcare gardens.

Yuliya Rashkovska

Yuliia Rashkovska is a Ukrainian landscape designer, PhD candidate, and specialist in therapeutic and rehabilitation gardens, as well as a member of the Guild of Landscape Architects of Ukraine. She is the founder of the “Therapeutic Gardens” initiative and the charitable foundation “Rehabilitation Gardens,” and the creator of healing spaces for children’s hospitals, rehabilitation centers for veterans, and community recovery environments. In her work, she combines evidence-based design, sensory landscapes, and social impact, exploring the role of nature in physical and emotional recovery. She has presented her projects at international events in Bergamo, the United States, and countries of the European Union, highlighting the importance of healing gardens in times of crisis, war, and human resilience.

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