At the most a jobbing builder comes in to hack the jungle to the ground when it is let to a new mob of students. Yet twice a year the garden puts on a prodigal show.
In April the summer snowflakes arrive, more and more each year, drooping snowdrop-like flowers on tallish spikes. They mix with the Spanish bluebells which grow in every neglected garden in north London. Then six weeks later the place is waist-high in meadow cranesbills: hardy geraniums with lots of small, veined flowers in colours ranging from greyish white to deep blue.
Both the snowflakes and the cranesbills started life in my own garden, but somehow managed to get their seed over a 4ft-high wall. Luxuriating in benign neglect, these two native species have gone on to create what the gurus of ecological gardening call a 'self-sustaining plant community'.
The other essential player has been the builder with his shears. Just chopping things down can liberate the potential of a patch of ground and create effects which are all the more powerful because they just happen instead of being laboriously contrived.
Last year I took charge of trying to introduce a more controlled approach to the wild garden at my daughter's school. This is a fenced area, with rich topsoil shaped into mounds and paths formed by railway sleepers; it is simply left to its own devices. Nature, with typical ingratitude, had responded to its diet of rich topsoil by forming an impenetrable sea of thistles and nettles. This may have teemed with rare life forms - but as no one tried to go too far into it, except to add to a collection of old supermarket trolleys, it was hard to be sure.
The place was officially called 'Derek's Wild Garden', named in honour of the late caretaker, who had created an immaculate formal garden which I was attempting to keep in order. The head, a gardening enthusiast, felt that it Could Do Better. After 150 years of urban life, the native flora of Holloway no longer has much that recalls the centuries during which it was farmland.
We agreed that I should try to turn it into a 'greatest hits' version of the English countryside.
We would keep some of the nettles and the shrubby buddleias, we decided - partly as a goodwill gesture to the butterflies, partly because it would be too much work to get rid of them all. But we'd also have a pond with frogs and bullrushes, hedgerow shrubs, primroses and bluebells in the spring, a flowering meadow for high summer.
Chucking the contents of a packet of poppy seed about failed to yield results. Planting strategic sites with perennial moon daisies and red campion, grown from seed and potted out in newspaper tubes, was more fruitful; I enlisted one of the classes at the school to do the actual planting.
This sort of gardening should not have to be hard work. In my experience, plants that happen to be wild flowers need little more than an occasional shearing back to check their exuberance. But the school's wild garden has been heavy going. I blame the soil, which I probably should have improved with grit or sand. This is a rich clay loam, which produces super-vigorous docks in a growing medium that hangs on to every last bit of their endless roots.
Impressive ecologies do not evolve overnight. The best flowering meadows, such as Cricklade in Wiltshire, have, their defenders will remind you, taken hundreds of years to develop their unique mixture of species. But with hands blistered from wrestling with docks and glowing with nettle stings, you want some payback right away. Never mind that a proprietory meadow seed mix will, according to the suppliers, have all its constituent plants in flower 'in later years'. What about right now?
One path to instant gratification is to add cornfield annuals. When sowing the meadow in the newly dug-over soil you mix in a blend which includes corn camomile, field poppies and corncockles, and for a few weeks of high summer in the following year it really looks as if you've pulled something off.
This impression is premature: a week or two later the tapestry of white, pink and red has turned khaki-brown, the baby meadow perennials are clustering around the dying stems - and so too is a sinister collection of baby docks, the descendants of the brutes drawn like teeth from the clay.
Bulbs are another ally. They give quick results and prevent the wild garden from being a one-season wonder - though I'm not sure whether any children actually turned out in chilly early March to shuffle past the wild daffodils (Narcissus pseudo-narcissus).
You could argue about whether bulbs of a wild plant are the real thing if they are the genetically identical products of a Dutch bulb firm. I recently went to Jacques Amand, the big Middlesex-based importer, for 50 Colchicum autumnale - corresponding, I hoped, to the native meadow saffron - to liven up the trim, but now flowerless, banks for the start of term.
But Autumnale, the only British colchicum, is the most difficult species - and what you buy is unlikely to be the wild form. The identical clones cannot be relied on to set seed. Amand's advice is to add a few bulbs of the white form and hope this stimulating divers-ity will guarantee them a fruitful sex life.
Some firms specialise in wild flowers and offer only native forms.
Naturescape, of Langar in Nottinghamshire, lists bulbs of lesser celandine, the little buttercup-yellow flowers which blanket country roadsides in the spring. I placed an order last year and waited - but in vain. Liz Scarborough, who runs Naturescape with her husband, Brian, revealed that their entire stock had been eaten by mice. This seemed at any rate proof that wild gardening does attract wildlife.
In the event I dug up some celandine from my father-in-law's garden just as they became visible in the spring. It felt like a brutal way to move bulbs and only their performance next spring will show how they reacted to it. The yellow-flowered water fringe was simply begged from the Alexandra Palace garden centre, which had none for sale but a congested wildlife pond bursting with the stuff. The primroses were dug from a friend's garden in the Chilterns, where they grow like weeds.
The seed mixture that we hope will create the meadow is devised by Emorsgate in Norfolk in conjunction with Terry Wells of the Institute of Terrestrial Ecology. To scrutinise this area over the months is to alternate between hope and foreboding. New species germinate all the time - but so do more and more docks. It is possible that repeated cutting and weeding will exhaust the over-rich soil and simply wear down the docks' will to resist.
As with the bulbs, native trees and shrubs can come from non-specialists. My father-in-law, who is a nurseryman, had stocks of common holly, spindle trees and a superb honeysuckle, a selected wild form called 'Graham Thomas'.
Other trees - hazel, blackthorn, Guelder rose, purple osier, alder buckthorn, dog rose - were bought from a big supplier of plants for landscaping schemes. The sweetbriar, old man's beard and hop arrived in the post from Naturescape, without any visible attentions from rodents.
It seemed almost as important to demonstrate that the garden could support wildlife as to get it in flower. The pond did the trick. Pond-skaters and even a dragonfly appeared almost overnight, undeterred by the heavy chemical smell of the new butyl rubber liner. With some oxygenating plants and scoopsful of water from a pond in the care of Islington council, the water was soon so teeming that you could hardly see through it, with a crowd of birds regularly gathering for an unappetising-looking drink.
One of the school governors supplied frog spawn in February. A population of tadpoles appeared, then dwindled to vanishing point, but it appears to have left a small legacy of immature frogs.
Apart from the pond, it is impossible to say whether more wildlife has been attracted by the new planting, which is still extremely underdeveloped, or lost with the taming of the docks and thistles. But on a hot summer's afternoon, there were enough insects in the flowering grasses to make working near them quite uncomfortable.
One of the schoolchildren came in to see if he could spot a frog. I asked what he thought of the garden. 'It's nice,' he said. 'A bit like my uncle's farm in Cyprus.' That farm is presumably freer of plastic bags and old crisp packets. But in the next few weeks an army of grasshoppers moved in, and when their chirrupping rose out above the traffic roar from the Seven Sisters Road you could almost buy the comparison.
Jacques Amand Ltd, The Nurseries, Clamp Hill, Stanmore, Middlesex HA7 3JS (081-954 8138). Naturescape, Lapwing Meadows, Coach Gap Lane, Langar, Notts NG13 9HP (0949 60592). Emorsgate Seeds, Terrington Court, Popes Lane, Terrington St Clement, King's Lynn, Norfolk PE34 4NT (0553 829028).