When Helen Penn moved into her south London home nearly 20 years ago the garden, like the house, retained many original features. Indoors this was a definite bonus, and fireplaces, cornices and sash windows gave the place character, but outdoors there was a distinct lack of it. The back garden, a quarter of an acre plot set out in straight lines and formal beds, was a throwback to Victorian strictness.

A spot of exterior redecoration was in order and Helen set about breaking down the orderly layout. She was assisted in her task by the great storm of 1987 when a huge poplar crashed down across the foot of the garden, destroying a greenhouse and necessitating some serious replanting.

The site of impact is now a pond and the tree stump in the far corner an overgrown wilderness. But vestiges of the the garden’s Victorian beginnings remain in the huge hedge which divides the garden in two and the apple, pear, apricot and quince trees which line one wall. Another fruit tree, a huge fig, sits against the back of the house, having won a reprieve when builders carried out subsidence work some years ago.

A well-established herb plot sits under the kitchen window but there are no vegetables. The garden - while large by London standards - would struggle to accommodate a fully-fledged vegetable garden, so Helen and her husband rely on a small holding in Kent for year-round produce and near self-sufficiency.

Instead, Helen has made this corner of SE22 a celebration of the sights and scents of flowers and foliage. “It’s at its best in May,” she says modestly, although it is still an impressive plot in high summer. In years past she has opened her garden to visits from the public, but decided against it this summer because work commitments have reduced the amount of time she could spend getting it in shape. “One year when we opened there were people sunbathing on the lawn which I thought was a bit off.”

But who could blame them? Helen’s garden is a very inviting space. Roses are a special favourite, recalling her father’s tastes in gardening. “I can still remember all the varieties of roses we had when I was a child - my father went in for red, white and blue colour schemes.” Among the other highlights are tree lupins, foxtail lilies, dark-leaved pansies and several varieties of peonies.

Helen’s search for unusual plants often takes her to the Royal Horticultural Society’s London headquarters in Vincent Square whose monthly shows are a meeting place for curious gardeners and specialist nurseries.

“Once you get into this gardening game chasing down really special plants can become something of an obsession.” But she knows her garden’s limits and, despite her fondness for rhododendrons, she would never attempt to introduce them. “Unless you go to ridiculous lengths you can’t get them to grow in a London garden.”

A senior fellow at London University’s Institute of Education, Helen put her research skills to good use while compiling her book, An Englishwoman’s Garden (BBC Books), inspired by her many visits to gardens up and down the country and the realisation that so many of them had been created by women. But few of her fellow academics can have such a pleasant working environment as her study, which opens into a sun-drenched conservatory wreathed in winter jasmine. Fittingly for someone whose specialist area of education is early years’ provision, all the available surfaces in the conservatory are given over to a nursery for plants in their formative stages - including tiny persimmon trees - and seeds, gathered from around the garden, drying out ready for planting next season.

The thick, creamy odour of magnolia wafts through to her workplace, and when she is not rattling off research papers on her word processor, Helen retires to the verdant oasis of calm next door. But she has always preferred pottering around to putting her feet up. “I find it almost impossible to sit still in the garden because there are always things to do. I’m training myself to relax more.”

Friends often pick her brains for horticultural hints. But the best policy, she tells them, is to be patient. “People ask me, ‘Can you help me with my garden?’ But the thing about gardening is that you have to keep at it. It takes at least five years to get anything good. Things like evergreen climbers and big roses take a long time to get established so you have to think of it as a long-term project.

“What I love about the garden is that there is variation every year depending on the climate. It is very pleasurable making things grow - sometimes you see things that are just beautiful and there are times of the year when it is truly spectacular.”