Introduction:The use of horticulture in mental health settings is widespread. Moreover, its effectiveness is supported by a body of qualitative evidence.Aims:The investigators in this research study sought to determine those aspects of their horticultural projects that conferred the greatest therapeutic benefit to their clients. They used outcome measures to rate the responses of participants, paying particular attention to the participants' expressed motivation.Method:Qualitative and quantitative methods were used to evaluate six horticultural projects. Ten participants were interviewed, using an adapted version of the Work Environment Impact Scale (WEIS) to rate factors that supported their motivation. Fifty participants were assessed, using the Volitional Questionnaire (VQ) to observe and rate the extent of their motivation.Findings:The therapeutic value of horticulture arose from a complex interplay of personal factors, including gender-based preferences, individual interests and social needs.Conclusion:The benefits of engaging in horticultural activity are not automatic. The external environment provides challenges, which can be graded by the facilitators to maximise the therapeutic benefit.