Spring, in the days of lockdown, continues obliviously – and reminds us how we depend on the natural world. For anyone with the luck to have a garden, the varied consolations of even a small patch of land will be clearer than ever. Sue Stuart-Smith’s fascinating book, written before the coronavirus crisis, brings indebtedness to nature into new focus and, during a time in which many of us are compelled by our phones and computers, extends the awareness – backed up by compendious and elegant research – of how mentally enriching it is to swap screen for green.

Stuart-Smith is a psychiatrist and psychotherapist, married to celebrated garden designer Tom Stuart-Smith. Their style of gardening is a sympathetic collaboration with nature, eschewing high-handed interventions. An early photograph – in 1988 – shows them surveying newly dug beds in their Hertfordshire garden. Nothing much is growing – apart from the baby in Sue Stuart-Smith’s arms – and they are at a momentary standstill, lost in thought. The photo makes the point: gardens begin – and continue – in the mind.

The book begins with the moving story of Stuart-Smith’s grandfather, Ted, whose submarine ran aground in the Dardanelles in 1915 and who became a prisoner in Turkey’s brutal camps. He returned a haunted wraith, wearing “a battered old raincoat with a Turkish fez on his head”. His fiancée, Fanny, restored him with sips of soup – but it was gardening that rescued him for the long haul. Ted is the first of many in the book for whom mental illness is relieved by gardening. Nature, Stuart-Smith reminds us, neither rejects nor judges.

As a young woman, she dismissed gardening as “outdoor housework”. Now, she reports on how a long gardening session can leave you “feeling dead on your feet but strangely renewed inside – both purged and re-energised, as if you have worked on yourself in the process…. gardening catharsis.” Gardening can help with grief and be a way of making peace with mortality. It is a “meeting place between our innermost, dream-infused selves and the real physical world”.

The neutrality of nurturing plants positively affects those who have themselves received little care, and Stuart-Smith enlightens us by explaining how caring is neurologically important. She visits exceptional therapeutic gardens including the Insight Garden project at San Quentin jail, Horatio’s Garden for spinal-injury patients at Salisbury hospital, and a vegetable garden for recovering addicts in San Patrignano, Italy. Plants are easier to deal with than people (even if they have their own ways of answering back).

This is not a book of effusions. It is attractive because quietly considered. It encourages us to garden – but gentle push never comes to shove. Stuart-Smith suggests that gardening, throughout history, has been civilising and about reciprocity – a mix of dream and slog. And there is no shortage of thinkers to stake her arguments. Freud was an avid orchid lover and cherished his garden in West Hampstead. Jung said: “We all need nourishment for our psyche. It is impossible to find such nourishment in urban tenements without a patch of green or a blossoming tree”, and Donald Winnicott recklessly climbed a tree towards the end of his life (to the alarm of his wife) to do some tree surgery and create a better view.

Stuart-Smith satisfyingly expands on Voltaire’s “Il faut cultiver notre jardin”. Rejecting conventional formality, Voltaire planted thousands of trees on his land in eastern France and asserted: “I have only done one sensible thing in my life – cultivate the ground. He who tills a field, renders a better service to mankind than all the scribblers in Europe.” Sue Stuart-Smith renders a very special service with this book. Let’s hope it reaches not only the converted but those who need it most.

The Natural Health Service makes a robustly argued companion piece that has grown out of fragility – the work not of a psychiatrist but of a patient. Isabel Hardman, assistant editor of the Spectator, has suffered from PTSD, been dogged by the Black Dog and had times when she has felt suicidal. In 2016, she knew something was wrong when words went on strike and “obsessive, frightening thoughts settled like a parliament of rooks”. It was, she has since discovered, the “great outdoors which made me want to keep living”. And while I wish she would not keep repeating “the great outdoors” (a phrase that diminishes what it describes), there is no doubting the integrity of her experience.

I respect her decision not to recount the terrible thing that happened to her, although it leaves one with a more than idle curiosity – knowing the details of an affliction can be part of assessing the cure. However, the book holds its own as an inquiry into nature as tonic. Elation comes in many forms: an unexpected orchid in a Glasgow car park, a shy kingfisher by the Thames, and Penny Black, a headstrong pony in Wimbledon. She writes about forest bathing and about walking, running and cold water swimming (she breaks the ice on the Serpentine – that most masochistic of life-affirmations). She never overstates her case. She acknowledges the need for more research, recognises the importance of placebos and remembers that each individual prescription will be different. These natural cures, she is especially keen to maintain, should be for everyone. And she introduces us to a wonderful Nordic word to which we should all adhere: friluftsliv – the healing power of nature.

• The Well Gardened Mind: Rediscovering Nature in the Modern World by Sue Stuart-Smith is published by HarperCollins (£20). To order a copy go to guardianbookshop.com. Free UK p&p over £15

• The Natural Health Service: What the Great Outdoors Can Do for Your Mind by Isabel Hardman is published by Atlantic (£16.99). To order a copy go to guardianbookshop.com. Free UK p&p over £15