Showing a better side of human nature: Jill Wolff cannot resist taking her shears to derelict city sites, says Anna Pavord

The new vicar rang the bell at Jill Wolff's home in Islington, north London. Did she ever go to church, he asked, more specifically his church, St Peter's, just around the corner in St Peter's Street? No, she said, she did not, but she fancied his churchyard like mad.

It was not so much a yard as a verge, a band of nettles, mud, broken bottles and waste paper that filled in a corner between the edge of the pavement and two walls of the church. Dr Wolff, who cannot look at any small piece of waste ground without wanting to plant something in it, felt that even if she did nothing for the inside of the church, she could at least make the outside look more appetising.

'You're on,' said the vicar. When Dr Wolff next walked to the church from her own charming garden there was no sign of the chain-link fence and barbed wire that previously surrounded the site. Nevertheless, she realised the daunting nature of her task.

The fence, although hideous, had stopped rubbish blowing in off the street and discouraged people from dumping mattresses, refrigerators and other household debris on the site. As fast as she cleared, new rubbish appeared. The first plants she managed to put in the ground disappeared overnight. She chose a notably thorny rose, 'Mermaid', to train against the church wall but that, too, fell victim the same day to a passer-by with iron gloves.

After five years, she said, she felt she was making an impression on the place. 'There was no money to spend, of course. Everything had to be obtained free.' She retrieved flagstones from workmen repairing pavements in the area and set them on edge, buried in the ground, to make a low barrier around the churchyard. She gathered up sycamore seedlings ('Always plenty of those,' she says) and made a low hedge inside the inverted paving stones. That at least stopped rubbish blowing in but failed to deter the nightly dumping of other sorts of garbage.

She kept the nettles, because they discouraged the constant depredations by cats and dogs. Among the nettles she planted valerian, foxgloves, golden rod and acanthus. She transplanted a 'Canary Bird' rose from her own garden and, miraculously, it stayed in its new home. Forsythia and kerria also became permanent fixtures and a laburnum invited itself in to join them.

For 20 years Dr Wolff fought to keep the verge covered in flowers rather than plastic bags and dog droppings. But the friendly vicar lost his battle to find a congregation in Islington and the church was eventually turned over to developers to become a block of flats.

The sawn-off trunk of the laburnum now stands like a gibbet by the boarded-up windows, and a few dusty remnants of the seedling sycamore hedge struggle to survive between the scaffolding poles. 'I was frightfully upset. But it was our own fault. None of us went to the church,' she says.

She turned immediately to another reclamation job: a tiny patch of waste ground that lay behind the offices of a charity with which her husband was connected. Sheer walls of other buildings on all sides cut it off almost entirely from the sun. It was like gardening at the bottom of a well. But she persuaded grass to grow, which was a miracle. She carried hebes and hydrangeas, bluebells and an 'Alberic Barbier' rose from her own garden to the black hole. Parking problems meant she could only garden there on Sundays. 'For a year I put my all into it,' she says. But then the charity moved offices and she lost that patch, too.

Fortunately, her biggest and most ambitious reclamation is safe. This is a series of interconnecting gardens behind one of the staff residences of Great Ormond Street hospital, where her husband was once Nuffield Professor of Child Health.

Originally there were 10 gardens in a row, separated by 6ft- high brick walls. Huge trees of heaven (Ailanthus altissima) shade the area and throw up suckers with pinnate leaves up to 3ft long. And as usual with Dr Wolff's gardens, broken slates, linoleum, rags and ironmongery lay in an inert mulch over the earth.

Dr Wolff persuaded the hospital's governing body to open up the space by making gaps in the dividing walls. With the bricks from that she made paths through the gardens. She clothed the walls with various ivies and jasmine and her favourite 'Alberic Barbier' rose. The heuchera, originally brought from Birmingham when the Wolffs came to London in the Sixties, and which has been in all her gardens since, was brought here, too.

In the heavy shade of the trees it flourishes surprisingly well with Solomon's seal, lilies of the valley and an indestructible creeping campanula. In one of the sections, Japanese anemones romp away. In another, day lilies and mahonia predominate. Once again she is operating on the cheap, 'liberating' her friends' indoor bulbs for use in the garden. Another supporter propagated all the hydrangeas that flourish there.

Still she feels an insatiable urge to reclaim orphan corners: 'I can't help it. My fingers twitch if I see any little bit of wasted ground.'

You will know she has run out of sites when you see the skips of Islington made fecund with trailing lobelia and impatiens.

(Photograph omitted)