Horticultural Therapy as an Intervention for Schizophrenia: A Review

Abstract

Background:

Schizophrenia is a mental illness that impacts multiple domains of a person's functioning therefore requiring multiple methods of treatment, which can become time consuming and costly. Horticultural therapy (HT) is a plant-based approach to reaching client goals and can do so in a holistic manner.

Methods:

A literature review was conducted in Google Scholar for “horticultural therapy” + “schizophrenia” and resulted in five relevant articles. These articles were evaluated through the Newcastle–Ottawa Scale and assigned a quality score.

Results:

HT administration and measurement were done differently across studies, yet HT was found to improve functioning in multiple domains, including social, vocational, psychological, and neuropsychological.

Conclusions:

HT seems to be an effective approach to addressing client concerns in more than one domain. This suggests that HT may be a more affordable, integrative, and time-conscious intervention for people with schizophrenia. However, the studies reviewed were of low quality and make it unwise to draw definitive conclusions. Future studies should follow set standards for conducting and reporting research.

Introduction

Schizophrenia is one of the most well-studied psychotic disorders. The diagnosis includes two categories of symptoms: positive and negative. Positive symptoms are an increase in problematic symptoms such as delusions and hallucinations, whereas negative symptoms are a decline in function, including diminished emotional expression and avolition, and a decrease in motivated behavior. In addition, those who exhibit schizophrenia may also struggle with dysregulated moods such as depression and anxiety, sleep disturbances, disinterest in food, and cognitive deficits, resulting in vocational and functional impairment. Schizophrenia has a lifetime prevalence of ∼0.3%–0.7% of the population with onset ranging from the late teens to mid-30s.¹ Most people with schizophrenia need daily living support and many struggle to maintain employment and social relationships.¹ Owing to schizophrenia being a chronic disabling condition, it is essential to treat it as effectively as possible to maximize the functional capacity of those diagnosed with the disorder.

The impact of schizophrenia is widespread within the brain, affecting structure, neurological function, and neuropsychological function. A review of 65 studies of medication-naive clients found several structures that differed from healthy individuals, including those that are responsible for functions such as voluntary movement, relaying sensory and motor signals, regulating consciousness and sleep, and executive functions such as decision-making and working memory.² Approximately 8% of medication-naive clients with schizophrenia experienced dyskinesia, or involuntary movements that often occur in the face and upper limbs, approximately 23% experience parkinsonian symptoms, and a self-reported 16% experience decreased pain perception.² Finally, neurological soft signs, or abnormalities in tasks that involve integrating senses and coordinating and sequencing motor patterns, have been reported by people with schizophrenia.² These neurological abnormalities indicate that it is not unusual for schizophrenia to involve movement and sensory integrating deficits. The most prominent neuropsychological abnormalities affect verbal and spatial memory, attention, and executive functioning (e.g., sequencing, organizing, and flexibility), with learning and language abilities also being negatively impacted.² Memory impairment is positively correlated with the severity of negative symptoms.² The neurological and neuropsychological abnormalities have typically been associated with greater differences between patients with schizophrenia and healthy controls compared with structural abnormalities. These differences are also detectible at young ages, such as children reaching developmental milestones late; achieving lower test scores; and struggling with motor skills, memory, and attention.²

Given the diversity of cognitive and psychological symptoms associated with schizophrenia, the types of therapy used to treat the disease encompass a variety of approaches. Medication has been found to be effective in decreasing psychosis relapse and decreasing the severity of relapses³ as well as decreasing mortality rates.⁴ Nonetheless, during an 18-month trial, 74% of participants discontinued their medication.⁴ Drug noncompliance in patients with schizophrenia is as high as 50%.⁴ Although neuropsychological impairments tend to be similar across medication-naive and medicated clients, medication tends to exacerbate structural^2,4 and neurological deficits.² Clients who have used antipsychotic medication have larger basal ganglia and thalami, which are involved in coordinating voluntary movement and relaying sensory information.² Dyskinesia rates increase once clients are introduced to any type of antipsychotic medication, as do neurological soft signs. It is important to both understand the naturally occurring neurological abnormalities in schizophrenia as well as the changes that occur once a client begins antipsychotics to be able to best understand the illness itself and the experiences of clients. Practitioners can better tailor treatments to meet the needs of their clients by understanding the structural and functional issues in those with schizophrenia. Because medication can exacerbate symptoms of schizophrenia, it is important to explore nonpharmacological interventions.

There are a variety of psychosocial treatments that work to improve functional recovery and cognitive abilities. These treatments include skills training, cognitive remediation, social cognition training, supported employment, and psychotherapy. Through these treatments, clients with schizophrenia learn to manage their symptoms, interact within recreational and occupational settings, improve their cognitive abilities, process emotions of self and others, and build a familial support system.³ Each type of therapy has been found to be effective in treating a specific aspect of schizophrenia. However, these effects remain domain-specific, requiring people with schizophrenia to seek several types of treatment to see holistic improvement.^5,6

Different integrated therapies have been attempted by combining previously effective treatments in a variety of novel ways. By integrating therapies, the goal is to reduce treatment costs and impact a wider range of outcomes. The only integrated therapy that has demonstrated greater improvement than the individual therapies it involves is integrated psychological therapy (IPT; combining social cognitive interventions and social skills into a cognitive behavioral therapy group). Although IPT is effective for many, increased research into different strategies of integration is needed to provide more customized care and options for providers and clients.⁶ Horticultural therapy (HT) is one such potential integrated therapy that merits more research due to its potential to improve several different domains of functioning in clients with schizophrenia through its unique plant-based modalities. HT and similar gardening-based interventions have shown promise across a variety of clinical diagnoses, including depression,⁷ anxiety,⁸ and schizophrenia.^9,10

HT is conducted by a trained professional who uses horticulture activities in a client-centered therapy that works to meet defined treatment goals.¹¹ Different countries have their own governing bodies for training and registering horticultural therapists. In the United States, the American Horticultural Therapy Association fills this role. To become a horticultural therapist, a person must earn a bachelor's degree in HT or complete the equivalent coursework (including psychology, horticulture, and HT classes) and complete a 480-hour supervised HT internship which includes direct client access and completing various projects. Currently, few manualized treatments exist, so the exact form of HT varies across settings and therapists.

HT helps clients to maximize all aspects of their well-being, including social, emotional, physical, spiritual, environmental, and intellectual. An example of a HT goal for a client with schizophrenia who is experiencing auditory hallucinations may be to direct attention away from the hallucinations to the desired activity. An objective that the client may try to reach within a session would be to concentrate on repotting plants for 30 minutes.¹² The process of working toward and achieving objectives and goals offers many benefits to clients, including an increased sense of responsibility and accomplishment, increased appropriate social interaction, an outlet to engage in self-expression and creativity, improved mood and lessened anxiety, new leisure skills and knowledge, improved functional skills such as attention and problem solving, improved vocational skills, and exposure to sensory-stimulating and grounding activities.¹² HT activities have the unique ability to help the client develop multiple areas of functioning within one activity, making it an efficient multifunctional therapy for clients with schizophrenia who experience a variety of impairments (see Table 1 for a more complete description of how HT can treat various symptoms of schizophrenia).

Table 1.

Examples of How Horticultural Therapy Can Treat Symptoms of Schizophrenia

Typical treatment	Domains improved	Example of how HT can treat
Medication and compliance	Psychosis, negative symptoms	Teach medication compliance through the client engaging in unprompted routines at the beginning of each session. Increase coping abilities for side effects and ways to maintain function despite the side effects.
Skills training	Manage symptoms and medication, recreational activities, problem solving, basic workplace skills	Present clients with a variety of activities to increase interest and likelihood of continued horticultural recreation. Give tasks with increasingly vague directions and/or present group with a problem to be solved. Expect basic work skills such as timeliness, appropriate dress, and staying on task.
Cognitive remediation	Attention, memory, reasoning, problem solving, auditory/visual perceptions	Increase amount of time expected to be spent on a single task. Increase length and complexity of directions. Provide grounding opportunities by stimulating the senses.
Social cognition training	Processing emotions, interpret social cues, empathy, attributional biases	Use group work to improve cooperation, connection, and comprehension.
Supported employment	Function in work environment	Expand upon basic work skills by expecting higher order functions such as independently selecting and completing tasks that need to be done.
Psychotherapy, family and/or psychotherapy	Familial support, symptom management	Incorporate families into HT. Work on therapeutic goals such as grounding and reappraising cognitions.

HT, horticultural therapy.

The objective of this review is to compare the effectiveness of HT to standard care in clients with schizophrenia. This review is important because the chronic nature of schizophrenia necessitates understanding different sustainable modalities of care and coping. In addition, understanding the effects of HT on schizophrenia will help to determine the therapy's current uses and benefits. Finally, understanding the underlying neurology of schizophrenia can be used to further improve HT treatments to best fit the symptoms and needs of clients with schizophrenia. By knowing areas of the brain most impacted and the functions they serve, practitioners may be able to more deeply understand typical deficits their clients experience and create interventions accordingly.

Methods

A search of Google Scholar through January 2018 used the terms “schizophrenia” and “horticultural therapy.” The search included articles that used HT and whose participants were diagnosed with schizophrenia. Articles were excluded when participants were not diagnosed with schizophrenia and when HT was not specifically used (i.e., if the focus was on therapeutic gardens). Relevant articles were found within the first 60 search results, and after that, no articles through search result 200 met inclusion criteria. Within the first 60 results, 48 articles were excluded due to not meeting criteria, and 8 were excluded for not being in English. A total of four articles were included. The reference sections of each article, in addition to the reference sections of other related articles, were examined to ensure no relevant studies were overlooked. Several potential articles were identified and examined, but only one study⁹ met all inclusion criteria. Five total studies were included (Fig. 1).

Figure 1.

Literature search process.

The five articles were reviewed for each of the following: aims, diagnostic criteria, design, method, and description of control and experimental groups. The methodological quality of the five articles is given in Table 2. The Newcastle–Ottawa Scale (NOS), a scale devised to assess the quality of case control studies by assigning a score of 0–8, was used to evaluate the selection of participants, comparability between groups, and methods of exposure to the treatment. Scores for the reviewed studies (excluding the case study, which cannot be assessed with the NOS) ranged from 1 to 2, indicating that the studies were of low quality. Oftentimes, low scores were assigned because information was lacking regarding each of the criteria areas (e.g., not specifying control group activities, not stating the type of data collected, and not sharing participant characteristics such as age). Review of the articles proceeded nonetheless due to a lack of alternative higher scored articles in the area of interest and because the quality of the studies was similar to others in the field of HT.

Table 2.

Summary and Quality Assessment of Included Studies

Author, year (location)	Participants	Summary of findings	Quality assessment
Oh et al., 2018 (South Korea)¹⁴	28 participants. Recruited from a mental health clinic and 2 mental health rehabilitation centers.	HT group participants had significant improvements in their positive, negative, and general symptoms as measured by the PANSS. The BPRS found significant improvement of clinical symptoms for HT participants. No improvement was found in control participants.	Aims were clearly described. Only some patient characteristics were shared (age, number of hospitalizations, gender, comorbid diagnoses). Specific outcomes (e.g., psychopathological symptoms or observed improvements) were not described. Criteria used to diagnose schizophrenia were unclear. HT group was one 2-hour meeting per week for 10 weeks and the activities for each session were briefly described. The therapists were certified HTs. Random assignment was not used. Control group activities were unclear. Participants were rated on two validated scales by a psychiatrist pre- and postintervention. NOS: 1
Son et al., 2004 (South Korea)⁹	25 participants in HT group, 25 in control (no activity) group, with “comparable levels of symptoms,” all were “accommodated for in a social welfare center” (whether that was inpatient or outpatient is unclear)	Participants in the HT group had a significant increase compared with the control group for self-esteem, interpersonal relationships, nonverbals, and substance of conversation. There was also a significant increase in participation, verbal interaction, self-concept, and identity in the HT group. The HT group experienced a significant decrease when compared with the control group in interpersonal sensitivity, depression, and anxiety.	Aims and outcomes were clearly described. Participant characteristics (e.g., age) were unclear. Criteria used to diagnose schizophrenia were unclear. Controls were schizophrenia clients at the same center as the HT group participants. Participants were given five scales before, during, and after the intervention. The HT group was for one hour, twice per week, for five months. NOS: 1
Wu et al., 2008 (Taiwan)¹⁵	Two HT groups were run, each with a control group chosen by the ward's occupational therapist. Group 1 ended with 9 participants per group, and Group 2 with 15 participants in the HT group and 14 participants in the control group. All participants had a “schizophrenia diagnosis.” Six participants from Group 1's HT group were in Group 2's HT group. Participants were inpatients at a psychiatric hospital.	Group 1's HT group improved, both from pre- to post-tests and when compared with the control groups, on attention. Group 2 showed a significant increase for the HT group in basic work skills, dealing with authority, orderliness/organizational skills, attendance, being on time, motivation, social space recognition, negotiation, group adaptation, automatism, and communication skills. Compared with the control groups, the HT groups reported feeling more relaxed, enjoying talking to others, feeling as if they learned new skills, and feeling less stressed. The participants who were in Group 1's and Group 2's HT groups experienced larger benefits than the new participants, but the differences between new and returning members were not significant. Areas that the returning members benefitted in that the new members did not include proper eye contact, proper words, personal hygiene, need for repeated direction, work without supervision, and coping with pressure.	Aims, participant characteristics, and outcomes were clearly described. Group 1's HT was once per week for 15 weeks, for 90 minutes each time, with the control group doing regular hospital activities. Group 2's HT was twice per week for 12 weeks, with the control group doing sheltered setting work. Criteria used to diagnose schizophrenia were unclear. Participants were given three surveys in Groups 1 and 3 different ones in Group 2, before and after the intervention. Attrition included five participants from Groups 1 and 2 from Group 2 due to discharge, refusal of test, withdrawal from program, and different diagnoses. NOS: 1
Kam and Siu, 2010 (China)¹³	Single-blind study of 24 participants randomized into two groups, 22 of whom had a schizophrenia diagnosis. Participants were recruited from sheltered workshops and other vocational rehabilitation services.	The randomization and scales were done by an independent assessor. The HT group (as opposed to the control) experienced a significant decrease in depression, anxiety, and stress. Qualitative results indicated that the HT group also experienced decreased work stress, improved social skills, an expanded social network, feeling respected, learning new skills, increased motivation, increased self-confidence, and an increase in connection to nature and horticulture as a leisure activity.	Aims, participant characteristics, and outcomes were clearly described. The HT group consisted of 1 hour per day of HT for 10 consecutive days, whereas the control group received standard care. Standard care included a variety of work-related tasks, both indoors and outdoors. Criteria used to diagnose schizophrenia were unclear. Attrition included two participants from the HT condition, reasons for which were unclear. NOS: 2
Minei et al., 2008 (Japan)¹⁰	Case study. One individual with chronic schizophrenia, male, age 74 years, participant in a geriatric daycare program.	During HT, participant talks to other participants and expresses his desires. Participant continues to water plants as part of his chosen routine.	Aims, participant characteristics, and outcomes clearly described. Criteria used to diagnose schizophrenia were unclear, although some symptoms that align with the DSM-5 were described (e.g., hallucinations and delusions). HT group was one time per week for 90 minutes. It was unclear whether objective data were collected. NOS: n/a

BPRS, Brief Psychiatric Rating Scale; DSM-5, Diagnostic and Statistical Manual of Mental Disorders, 5th edition; n/a, not applicable; NOS, Newcastle–Ottawa Scale; PANSS, Positive and Negative Syndromes Scale.

Results

HT was administered in diverse settings and with diverse methodology and was found to improve several domains of functioning, including social, vocational, psychological, and neuropsychological. All studies were found to offer benefits in several domains for clients with schizophrenia.

The amount of time spent in HT sessions, the leaders of the sessions, and the activities within each session varied by study. The HT groups in the studies reviewed met one to two times per week, were 90–120 minutes in length, and lasted 10–15 weeks. The one exception is the group studied by Kam and Siu,¹³ which was 1 hour per day for 10 consecutive days. The groups were run within inpatient units, at day programs, and as stand-alone programs. Some programs were run indoors, some outside, and some included both locations. Although most articles did not specify who led the HT groups, two identified their leaders as including an occupational therapist¹³ and a horticultural therapist.¹⁴ Kam and Siu¹³ included activities such as touring the garden, learning about organic farming, learning to water and fertilize plants, weeding and working with the soil, harvesting, identifying and drawing herbs, making a scarecrow, making herbal tea, potting plants, and visiting a greenhouse. Minei et al.¹⁰ included cultivation, cooking, and making crafts. Wu et al.¹⁵ incorporated plant identification, propagation, craftwork, and harvesting produce. Oh et al.¹⁴ included making a vegetable garden plot, fertilizing, planting, hydroponics, mulching, harvesting, weeding, pest control, and making tea. Son et al.⁹ did not describe what occurred during the HT groups.

Social skills were found to improve in a variety of ways, including verbal interactions with others,^9,10,15 communication skills,^13,15 expanded social network,^9,13 understanding of nonverbal communication, decreased interpersonal sensitivity, improved substance of conversation,⁹ increased social space recognition, proper eye contact, improved personal hygiene, and improved group adaptation.¹⁵ Improvements that were seen, but did not reach statistical significance, included interpersonal behaviors such as independence, cooperation, communication, response to commands, and therapeutic relationships.⁹ Areas that did not see improvement included relationship stability,¹⁰ participation, responsibility,¹⁵ and interpersonal relationships (as assessed by the Social Behavior Scale, which assesses verbal, nonverbal, and substance of conversation).⁹

Vocational skills improved in several ways, including learning new work skills,^13,15 dealing with authority and negotiating, basic work skills, attendance, being on time, needing directions repeated less, working without supervision, working automatically, coping with pressure,¹⁵ increased participation,⁹ and decreased work stress.¹³ Work behaviors on the Work Behavior Scale did not improve,¹³ and there were not improvements in vocational adjustment.⁹

Psychologically, participants experienced several benefits, including decreased anxiety and stress,^9,13,15 decreased depression,^9,13 increased self-esteem,^9,13 greater engagement in new routines/leisure activities,^10,13 feeling respected, feeling a connection to nature,¹³ decreased positive and negative symptoms, decreased general and clinical symptoms,¹⁴ increased motivation, increased organizational skills, increased verbal skills,¹⁵ increased expressing of desires,¹⁰ improved self-concept, and improved self-identity.⁹ Areas that did not see improvement included need-drive adaptation, exercise-perceptivity,⁹ subjective quality of life, phobic anxiety, frustration tolerance, paranoid ideation, psychoticism, obsession, and hostility, although previous research has shown obsession and hostility to decrease after HT.¹⁵

To understand neurophysiological effects, Son et al.¹⁶ used an electroencephalogram (EEG) to examine the difference between people with schizophrenia viewing a plant compared with viewing a blank wall. The purpose was to eliminate the bias of using nonpeer-reviewed measures that is common in HT studies as well as to understand some of the physical changes that occur in patients with schizophrenia when simply viewing a plant. In the plant-viewing condition, δ waves decreased, indicating that brain activity increased in locations associated with attention, motor planning, and working memory.⁹ Increased activity in these areas from simply viewing plants demonstrates the impact that HT can have on impairments that clients with schizophrenia often experience. The study also found that the plant-viewing condition resulted in decreased heart rate and blood pressure, which in previous studies of individuals with and without a variety of diagnoses indicated decreased stress and increased overall health.⁹ Using techniques that track neuronal activity or involve neuroimaging can be beneficial to HT by confirming which parts of the therapy activate the areas that the therapist is attempting to change. These tests can also provide a new way of examining and understanding HT, specifically its effects on people with schizophrenia.

Discussion and Conclusions

Overall, the most consistently found improvements included interacting with others, communication skills, larger social networks, learning new skills, dealing with authority, decreasing anxiety, decreasing depression, increasing self-esteem, engaging in new activities, and increased motivation. Although each area of functioning (social, psychological, neuropsychological, and vocational) showed areas of improvement and areas of no change, it was more common to find benefits than to find that participants were unaffected by the intervention. In addition, no areas of functioning were reported to decline as a result of HT. Likely reasons behind the slight discrepancies across studies include using different measures and different types of HT interventions.

These improvements are important to note because the singular treatment of HT was able to provide improvements across a variety of domains, including social, vocational, psychological, and neurophysiological. This indicates that HT is an integrative treatment option that merits further study. Integrative therapies, such as HT, offer the benefit of being more time and cost efficient and offer additional stability for clients as they are able to receive benefits in one location with one therapist, as opposed to several different therapies. There is also evidence that increased time in HT relates to increased benefits, as demonstrated by Wu et al.,¹⁵ who compared clients in their study who had and had not been in HT before, finding that those who had recently been in HT experienced benefits above and beyond those who had not.

Further studies should look to increase the quality of the research and/or the written report of the research, by using and describing methods such as randomization, diagnoses confirmation, and community controls. Further studies should be clear about treatment goals and objectives to best assess which activities and approaches best help with each symptom or functional impairment. Assessments should be conducted with validated instruments and follow a priori methodology. A more detailed description of which interventions are used and who implemented them would also be useful. Additional research should be conducted to assess whether results are consistent across different cultures. It is also important for future studies to focus on empirically supported techniques in therapy. The field of HT is fairly new, particularly with regard to research, so utilizing empirically supported techniques as well as more elaborately describing the methods used would likely lead to wider acceptance of HT. Neurological imaging and assessment could also be incorporated both as a pretest/post-test measure and as a during-activity measure, such as Son et al.'s¹⁶ study on plants and EEG. The addition of neuroimaging techniques would help to identify both in-the-moment changes in functioning and longer term changes that occur due to the intervention. By using what we know about the neuropsychology of schizophrenia and the effects of HT on clients with schizophrenia, HT interventions can be better tailored to maximize their effectiveness for improving the lives of those with schizophrenia.

Footnotes

Author Disclosure Statement

No competing financial interests exist.▪

References

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders: DSM-5. Washington, DC: American Psychiatric Association, 2013.

Torrey

. Studies of individuals with schizophrenia never treated with antipsychotic medications: A review. Schizophr Res, 2002; 58:101–115.

Janicak

, Marder

, Tandon

, Goldman

. Schizophrenia: Recent Advances in Diagnosis and Treatment. New York: Springer, 2014.

Morrison

, Turkington

, Pyle

, et al. Cognitive therapy for people with schizophrenia spectrum disorders not taking antipsychotic drugs: A single-blind randomised controlled trial. Lancet, 2014; 383:1395–1403.

Bustillo

, Lauriello

, Horan

, Keith

. The psychosocial treatment of schizophrenia: An update. Am J Psychiatry, 2001; 158:163–175.

Patterson

, Leeuwenkamp

. Adjunctive psychosocial therapies for the treatment of schizophrenia. Schizophr Res, 2008; 100:108–119.

Gonzalez

, Hartig

, Patil

, et al. Therapeutic horticulture in clinical depression: A prospective study of active components. J Adv Nurs, 2009; 66:2002–2013.

Clatworthy

, Hinds

, Camic

. Gardening as a mental health intervention: A review. Ment Health Rev J, 2013; 18:214–225.

Son

, Um

, Kim

, Song

. Effect of horticultural therapy on the changes of self-esteem and sociality of individuals with chronic schizophrenia. Acta Hortic, 2004; 639:185–191.

10.

Minei

, Kiyuna

, Tanaka

, Takaesu

. Horticultural therapy for the aged with chronic schizophrenia. Acta Hortic, 2008; 790:63–66.

11.

Haller

, Capra

. Horticultural Therapy Methods: Making Connections in Health Care, Human Service, and Community Programs, 2nd ed. Boca Raton: Taylor & Francis Group, 2016.

12.

Simson

, Straus

. Horticulture as Therapy: Principles and Practice. Binghamton: The Food Products Press, 1997.

13.

Kam

, Siu

. Evaluation of a horticultural activity programme for persons with psychiatric illness. Hong Kong J Occup Ther, 2010; 20:80–86.

14.

, Park

, Ahn

. Assessment of the psychopathological effects of a horticultural therapy program in patients with schizophrenia. Complement Ther Med, 2018; 36:54–58.

15.

, Chang

, Hsu

, et al. The beneficial effects of horticultural activities on patients' community skill and motivation in a public psychiatric center. Acta Hortic, 2008; 775:55–70.

16.

Son

, Song

, Um

, et al. Effects of visual recognition of green plants on the changes of EEG in patients with schizophrenia. Acta Hortic, 2004; 639:193–199.