Is that your garden?’ my friend Michele, who was smoking a cigarette out of our kitchen window, gestured down at the bramble jungle below that was, technically, our garden.

‘What a waste,’ he said. He was staying with us in north London while he flat-hunted and most of the places he saw didn’t even have a living room, let alone outdoor space.

He was right: it was a waste, but it was also a challenge. The patch of land, once part of a bigger garden belonging to the house we lived in before it had been divided into flats, may have been overgrown but it was still a large space. We had tried a few times before to cut back the brambles, and every time they seemed to reappear practically overnight. A proper garden required time, hard work and maintenance, and we were in our 20s, more interested in sampling what the bars of London had to offer than wielding a trowel. But then I became ill, and everything changed.

My generation, the millennials, have been called the most anxious generation in history. We are told that we are living through ‘an anxiety epidemic’, not helped by technology, perfectionism, economic and housing pressures and work stress. One in four people in the UK experiences a mental health problem every year and, according to a Cambridge University report, more than eight million people in the UK suffer some kind of anxiety disorder, with women and those under 35 especially affected.

SALONIdress, £575, at 

In 2010 I was assaulted in the street after coming home from a night out and as a result developed PTSD. After some excellent NHS treatment I got better, but following the Paris attacks in late 2015 it came back worse than ever. I felt under constant threat, spending all day every day terrified that I would die. I became, essentially, agoraphobic: I was too frightened to take public transport or go to busy parts of town. I stopped going to bars and restaurants or to the cinema or shopping centres, and I started having frequent panic attacks. I just about managed to hold down my job because luckily I was a freelancer, but the scope of my life shrank dramatically. My world, which had once felt limitless and brimming with the potential for adventure, narrowed to a pinprick.

Although my anxiety disorder was extreme, I recognised some of the symptoms, particularly with regard to panic attacks, from experiences my peers had shared with me. They had tried exercise, dieting and meditation apps to complement medication and therapy, but no one I knew my age really did any gardening. It simply would not have occurred to me had I not, essentially, become a recluse.

And so my boyfriend, Tim, now my husband, built me a garden. It remains the most romantic thing that anyone has ever done for me. Even going to the local shop made me extremely anxious, so I was spending much of every day indoors. A garden, he concluded, would at least allow me to get some sunlight. So he cut back the brambles and then dug up their many-tentacled roots, some of which were bigger than his head, so they wouldn’t come back. He and his brother took all the junk that had accumulated (rotting garden furniture, rubbish, firewood etc) to the tip, uncovering a litter of baby foxes in the process. We felt guilty kicking them out of their home, but they retreated to our neighbour’s still-overgrown patch and now pop back for a visit occasionally.

We decided how much space we would be able to cultivate and covered the rest with gravel. We didn’t know how much energy I would have so didn’t want it to be too high-maintenance, deciding to designate a large patch to a wildflower meadow, which would encourage bees and butterflies. Then Tim dug out flower beds. With help from a colleague of his with a sideline in garden design, we decided which plants would be best where and I set about planting. I had always loved roses, lavender, clematis and jasmine, so I already had a vague idea what I wanted: the feel of a traditional cottage garden that wasn’t too manicured or difficult to maintain.

RhiannonCosslettin her garden

It was a learning curve. We didn’t have huge amounts of money to spend so whenever I planted something that ended up withering and dying, like my first jasmine plant did, it was a bit of a blow. I relied on YouTube tutorials and the indispensable Royal Horticultural Society website for information, as well as friends, neighbours and family. Everyone was so generous with advice, not to mention cuttings. My grandmother gave me forget-me-not and love-in-the-mist seeds, my mum’s friend Jane from up the road dispensed advice, my neighbour popped round with a lovely plant with pink flowers (I’m still working on my identification skills). After feeling so isolated, my new hobby gave me a sense of community and shared interests, and revived my social life. Friends came over for barbecues or drinks in the garden, and I slowly began to enjoy myself again.

When I had started going into the garden at the worst point in my illness, a plane would fly overhead and I’d be genuinely terrified it would fall from the sky. But being re-exposed to the outside world in a way that wasn’t too demanding set me on the road to recovery. I imagine the exercise and vitamin D helped, too, as well as the sensory aspects of being in nature — the smell of the roses, the feeling of my hand plunging into damp compost, the sounds of the birds. There is something quite meditative about it, and it is, ultimately, the kind of environment in which we have evolved. We forget how unnatural our artificially lit and air conditioned offices are, how perhaps they are not actually so good for us.

It wasn’t just the gardening that cured me of my anxiety, of course. Mental illness is not so simple, and it took a lot of therapy and a course of medication to make me better again. But I credit gardening with having played a huge role in my recovery. At a time when my anxiety was so bad that at times it felt that I had little left to live for, the discovery of a new passion gave me a reason to keep going, a reason, even, for enthusiasm. There’s a sense of fulfilment that comes from nurturing something into being. I was so delighted when my wildflower meadow erupted into a sea of cornflower blue that first summer. I had been inside my own head for so long, feeling so helpless as obsessive, frightening thoughts percolated around and around, that I had forgotten what it meant to be outward-looking. I saw those flowers and it was as though Mother Nature was saying, ‘Look: life. It can be beautiful.’ It might sound sentimental, but when you’re in a well of such darkness, you don’t imagine you’ll find anything beautiful again.

It is perhaps unsurprising that, after such a severe period of PTSD, that trauma has come to permeate the novel I was working on, The Tyranny of Lost Things. It is not an autobiographical novel but there is one short scene in which Harmony, the protagonist, and her eccentric downstairs neighbour, Coral, clear the back garden. I also wanted to pay tribute to the garden in some small way, for the contribution it made to my recovery.

It has been two years since Tim built the garden and it’s still a work in progress but I’m already very proud of it. My pink climbing roses exploded this year, mixing with the sweet-smelling honeysuckle that I planted against the fence. The love-in-the-mist and the lavender combined to make a beautiful flower bed. Having had such good success with the roses — they are, after all, basically brambles and seem to grow with similar ferocity — I have planted more. Who knows how my garden will grow next year? It’s never the same twice and that’s part of why I love it.

Gardening might not be cool or edgy, but I can see why it’s becoming popular with my generation. It gives you a feeling of investing in something, and in these unstable times that is hard to beat. These days I’m almost fully recovered and off medication completely, but I still have bad days sometimes. When I do, I make sure I get down there. It always helps.