Weeds are the tough customers of the plant world, brazenly colonizing any available space in the garden when your back is turned. Ground elder resurrects itself from the tiniest scrap of root; the dandelion's delicate spores spread with the mildest puff of wind; Japanese knotweed thrives so well in the British climate that it can punch its way through tarmac and concrete; and the burnt red spikes of curled dock produce up to 30,000 seeds per plant in a single summer.
Both infuriating and awe-inspiring, weeds seem to be having their moment. A handful of books about them have appeared this year, including John Walker's Weeds (2003), which suggests an organic approach to combating these garden intruders, using such methods as deep burial, smothering, flaming, decapitation, drowning and soaking in urine. Weeds have also been taking root in a few galleries. Michael Landy's Nourishment (2003), for example, is an exquisite series of etchings of weeds collected from urban sites and nurtured at home with the meticulous care usually reserved for newly discovered orchids. Jacques Nimki, working at Camden Arts Centre, collected weeds from the congested Finchley Road area surrounding the centre and created a visual anthology of his findings, Florilegium (2003).
Meanwhile, over the last ten years or so the work of garden designers such as Piet Oudolf and Dan Pearson has firmly established the trend of naturalistic planting. This year's Chelsea Flower Show, for example, saw Grecian temples, disused boat houses, a rusty clapped-out Mini and pebbly brooks, along with tons of slate and other natural materials, used as backdrops for shabby-chic gardens. The journal The Garden decreed that horticultural Minimalism is now out of fashion and that the distinction between planned gardens and natural countryside is becoming every more blurred.
So the theme of this year's 11th Chaumont-sur-Loire Garden Festival - 'Weeds!' - was intriguing. Set in gardens designed by Jacques Wirtz in the grounds of a château overlooking the Loire, the event has a reputation for challenging attitudes to garden design; past themes have included 'Ricochets', 'Pleasure', 'Imagination in Crisis' and, last year, 'Eroticism in the Garden'. This year it explored its subject from every conceivable angle - from the musical potential of weeds (who hasn't taken a piece of grass and made a whistle from it?) to their medicinal properties. The festival restaurant also warmed to the theme, serving a special menu that included eel marinated in weeds found on the banks of the Loire, snails served on a bed of nettles, and foie gras with a salad of stitchwort.
The idea of a 'weed' is, of course, a manmade construct: a weed is only a weed if it grows in a cultivated land; elsewhere it is an indigenous plant. As the press kit for Chaumont pertinently asked, it is a moot point whether the real invaders are the weeds or the cultivated plants introduced by the gardener. Some of the gardens on show took this very literally, with prison grilles and rusty steel cages symbolizing the human persecution of weeds. Turning the tables, human debris became the weed in Julien Mizermont and Cécile Califanos' hallucinogenic garden: a single teaspoon left behind after a picnic, like a lone seed, had multiplied to become a 30,000 strong army of teaspoons, buckling the lawn under their insurgent pressure and cleaving it away from the land in enormous bow shapes. The picnic theme was reflected in the surrounding red and white chequered beds, with feathery white cosmos and dashing red dahlias. But these gardens tried too hard to play with the theme, forgetting to make the planting actually look interesting.
To greater effect some designers relished and celebrated specific weeds and their varying characteristics. To reach L'Oracle de Lemma (Jean-Marie Desgrolard, Jean Marie Blanchet and Joël Dufour) you had to pass through a narrow path of tall grasses and ferns to emerge in front of Carl Andre-style floor sculpture, the square slabs of which were composed alternately of pieces of mirror and shallow areas of water covered in duckweed (Lemma minor). Coils of metal scattered amongst the geometric floor pieces hinted at an industrial wasteland in an understated shrine to a plant that rapidly covers water surfaces with its tiny leaves of milky green.
A Fakir's Repose (Claire Belloc), meanwhile, rejoiced in the spikiness of the thistle. In keeping with its name, there was not one square inch to stand or sit on comfortably: every surface, path and chair was covered in broken glass and metal spikes. The triangular pond was coloured blood red and the prickly planting scheme was a forest of blue-headed Echinops, Eryngium gigantum and other less than friendly-looking plants. Steel-coloured artemesia provided a backdrop for the thistles and metal spikes, with what looked liked metal bottle-brushes on the end, which were placed throughout the border at various heights - just in case the thistles weren't looking quite mean enough that day.
Some of the most successful designs were those that eased up on the rhetoric and theatrics but took as their inspiration how weeds occupy wasteland. Antonio Perazzi and Masayo Ave constructed a smooth concrete circle in the middle of their space, which could have been the edge of supermarket car park. A couple of cracks and dents had allowed room for Helicysum angustifolium to nestle and produce its undernourished-looking, scruffy yellow flowers.
Rusty metal poles and clothes lines criss-crossed Abandonment (Tal Lancman, Lauri Macmillan Johnson, Hili Sonia Mann, Maurizio Galante and Cécile Dalladié) with remnants of what at first glance looked like an old woman's bedraggled, sun-bleached washing, now abandoned and overgrown. On closer inspection the clothes were textured with intricate stitching and tiny pouch-shaped pockets (for seeds?) and were actually the work of fashion designer Galante. Such was the vigour of the weed invasion that it was impossible to venture far into the garden, but from within its heart came the persistent chirp of grasshoppers; while murky patches of water created a sinister atmosphere. The muted colours of the planting felt as washed out as the clothes, with tentacles of wild peas twisting their way between pale pink vetch, and the frothy heads of meadowsweet and foxglove spires against a host of nettles and grasses meant the boundaries of the garden were entirely lost to view.
A garden that shared not only the washing-line theme (in this case three whirlygig lines with their prongs open like small trees) but also the sense of overwhelmed domestic space was Hang-out in the Open Air, by Peleszko and Bigault. A barely discernible patch of corn gave the impression this must once have been a vegetable patch. The washing-lines had obviously not been touched for a while either, since bindweed had engulfed them, and at their base enormous flesh-coloured poppies were shedding their petals. Lavender, lemon balm and rosemary among clumps of nettles and ragwort made for an aromatic sensation and an insect feast.
If weeds are a relatively modern concept, several gardens attempted to hark back to the time before any such classification existed. Underfoot at the entrance of Sewing the Seeds of Doubt (Mélanie Claude and Valerie Barraès) was dark volcanic sand and three skeletal blackened trees, with only the odd tuft of festuca grass breaking through. This quickly gave way to an avalanche of brambles, wild roses and grasses, beyond which was a Modernist garden of white stone, 1960s retro plastic and lines of yellow Peruvian lilies (alstroemeria) and white agapanthus. A subtler take on the weed as the precursor of the garden was by Christophe Ponceau and Betrand Houin, who had created a totally enclosed environment with a net ceiling dripping with climbers, to reduce the light level, and a constant light sprinkling of water coming from the roof, which sent one straight to the rain forest floor. Several varieties of ferns flourished in this damp enclosure, as did the large leathery-leafed gunnera, which adds a touch of the primeval wherever it is planted. With the Disney-esque turrets of the Château de Chaumont peeping above the garden, Jurassic Park did not feel far away. One Italian entry, meanwhile had a touch of sci-fi, with allegedly genetically modified weeds sprouting out of test tube-like glass spheres with small holes in them, deposited on the landscape like weapons of biological warfare.
The desire to rid one's garden of weeds is in essence wanting to play God with one's own little patch of turf, making a garden more spectacular than nature. But from the look of some of the gardens of Chaumont perhaps we should let the weeds take over a bit more, put our feet up in a shady spot and tuck into the Escargots sur un lit d'orties fraîches.