I've published an article in The Conversation about the therapeutic benefits of gardening.  See the link below:
https://theconversation.com/the-science-is-in-gardening-is-good-for-you-65251

Here's the first paragraph. 

The science is in: gardening is good for you

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“That’s all very well put,” says Candide, in the final line of Voltaire’s novel of the same name, “but we must go and work our garden.”
I studied this text at high school before I became a gardener and professional horticulturist. We were taught that Candide’s gardening imperative was metaphorical not literal; a command for finding an authentic vocation, not a call to take up trowels and secateurs.
In fact, Voltaire himself really believed that active gardening was a great way to stay sane, healthy and free from stress. That was 300 years ago.
As it turns out, the science suggests he was right.


There's also a link to my colleague Steven Wells (nurse and gardener extraordinare) talking about his work as a horticultural therapist and garden creator in hospitals.