Stuart-Smith is a medical doctor but her first love was literature. This might have something to do with the directness of her personal writing. She has the detached warmth of the perfect therapist. And she has the gift of wearing her remarkable learning lightly. Stuart-Smith wasn't always a gardener. At Cambridge, studying literature she says that to her "gardening was a form of outdoor housework and I would no more have plucked a weed than baked a scone or washed the curtains". Gardening came into her life because the man she loved loved gardening and she decided to love what he loved.

Although, the experience of a garden and its ability to heal the spirit and the body has always been visible to her. Her grandfather, Ted May, was a submariner in the First World War. Enlisting at 15, he was captured and interned in Turkey and endured cruelties so perverse that when he finally escaped and came home he was not expected to live. He also had profound post-traumatic stress. In 1920 he signed up for a year-long course of horticulture and his life turned around. His granddaughter remembers him best in the context of his gardens.

There are chapters that tell the stories of the benefits of gardening in the direst urban areas; plant a tree, put in a bench and the crime rate goes down, in prisons, for those those with PTS. But the most surprising chapter is called War and Gardening. Churchill, said the poet Siegfried Sassoon, thought war and gardening were the two normal occupations of mankind. Was he mad? Well, aren't we all now and then, but Churchill, a gardener, was on to something. In the trenches soldiers, both sides, made gardens. Not products of boredom, but beautiful, tended and productive plots made for beauty, eloquent with silent hope. That men in extremis gardened like this is as unbearable as it is uplifting.

Freud was also passionate gardener, a great lover of orchids and gardenias. His last year, the final journey towards death, was made more bearable by the garden at his London house. Jung, too, liked nothing more than living in Spartan conditions on the woodland shores of the lake in Zurich. He saw few people, chopped wood and grew potatoes. People who enjoy thinking have observed that gardening, becoming intimate with the seasons, turns our greatest adversary, death, into something ordinary. Remember Montaigne, who famously said he hoped death would find him planting in his cabbage patch?

And Voltaire, intimate of kings and queens, the most renowned philosopher and talker of his time, lived on his estate in Ferney near the Swiss border for the last 20 years of his life and gardened. He said this: "I have only done one sensible thing in my life – to cultivate the ground. He who tills a field renders a better service to mankind than all the scribblers in Europe." I suspect, though, he would bend the knee to this particular scribbler, and gardener. I do.