Urban waste grounds are unwanted, forgotten and often also overgrown areas - abandoned spaces in cities that have been taken over by wild plants. These may be ‘unkempt’ yards, closed railway or tram tracks, areas adjacent to road infrastructure, cemeteries, abandoned buildings… Often referred to as empty spaces, they are in fact full of wild vegetation.

Waste grounds are used by wild plants, insects, birds and other animals. They develop spontaneously and play a crucial role in urban ecosystems. As such, they deserve a new, much more positive name.

Gilles Clément is a French botanist and landscape architect who coined the phrase ‘third landscapes’ to talk about wild gardens growing on urban waste grounds. Like many contemporary landscape architects, Gilles sees the value of such places and admires their unique beauty.

For a wild garden to be called a third landscape, it has to form spontaneously, without human help or involvement. This is completely different to an ordinary garden, where seeds are sown, saplings planted and plants trimmed and tended. Third landscapes happen on their own. Such gardens are ‘cultivated’ by nature. Apart from urban waste grounds, they include nature reserves, roadsides, mountain slopes, overgrown railway or tram tracks and other places that are inaccessible to humans.

A bird’s‑eye view of a city reveals a number of green spots. Apart from large patches of parks and gardens, small blots of green are also visible between the greys of roads and pavements and the multicoloured mosaic of roofs. Many of these blots represent third landscapes - wild gardens that formed out of their own accord.

Although they are very small, such blots are important for the urban ecology. Ecology stands for the ties and interactions between various organisms and the environment they live in. Consequently, we can talk about ecology to describe the interrelationship between plants and insects that coexist in one place, and how they in turn influence their surroundings. The more plants there are, the more insects they are going to attract. Spots of wild vegetation provide food and shelter to a number of animal species. These small oases are home to a multitude of plants and animals, increasing urban biodiversity.

Some third landscapes are so small that one almost requires a microscope to see them - or at least a magnifying glass. They rise a mere few millimetres above the ground and we trample them unawares, not noticing the thin green strands that start growing between the pavement blocks. ‘Interpavement’ gardens is where we may often find the so-called bird knotgrass (or Polygonum aviculare, to quote its botanical Latin name).

The Polygonum species are very popular weeds with many beautiful names. Some common nicknames include knotgrass, knotweed, tearthumb, mile-a-minute and smartweed. Seeds of the plant are a treat for various types of birds - hens, geese, ducks, linnets, greenfinches and sparrows, hence the name of this particular species: bird, or aviculare.

Weeds can survive in very difficult conditions. They grow in places that are too cold and dark for other plant species, where soils are lacking in micronutrients. To endure and thrive, they require but a minimum amount of water, a handful of soil and access to light.

At first, only individual specimens may be found in such demanding habitats. With time, as they die in winter, they fertilize the soil and their roots scarify, aerate and bind particles of soil. The plants scatter their seeds or proliferate and small spots turn into larger green carpets as the years go by. Flowering from spring to autumn, they attract insects with their nectar and are home to small rodents and bugs. A small urban ecosystem is born.

The word ‘weed’ means an unwanted and unwelcome plant. In the past, it mostly referred to unsolicited plants that appeared in crops. Right now most wild plants classified as ruderal plants are popularly referred to as ‘weeds’.

Do ruderal plants grow on ruins? Yes, but not just there - they appear in places that have been strongly transformed by humans: in abandoned buildings and their surroundings, on urban waste grounds, brownfield sites, edges of roads or roadsides, parking lots, squares, landfills and rubbish heaps. They are the first ones to appear in what often are very difficult conditions - there is little light, water is scarce and soil is often replaced by rubble. Ruderal plants pave the way for more demanding species, which eventually also show up in the ruderal garden.

The common nettle (Latin: Urtica dioica) is the most well-known, though not particularly popular weed. This plant can brutally sting our skin if we carelessly enter its territory. Nettles also bring to mind unkempt gardens, rubbish heaps and piles of rubble – everyone seems to be ashamed of them.

In fact, like a number of other weeds, the common nettle has a number of positive properties. Its image of a black sheep among herbaceous plants should really be subverted.

First, this is a medicinal plant, rich in vitamins. Nettle tea helps relieve fatigue, arthritis and kidney problems. The plant can also be used to cook delicious soups, casseroles and quiches or make nettle shampoos, soaps and other cosmetics. Stinging nettle is a plant of many virtues.

Wild lawns are created by low-growing weeds, mostly of the Poaceae family of grasses. They are in stark contrast to evenly mowed English lawns found on football pitches and in gardens. Wild lawns are home to a multitude of plants (mostly grasses) and are much higher than the mowed ones. Unmown grasses form flowers, blossom and bear fruit, feeding birds and insects. English lawns, though highly popular and pleasant to the eye, represent a green desert from a botanical perspective and hardly provide any nourishment for insects.

Couch grass (Latin: Elymus repens) is one of the species found on wild lawns and a particularly unwelcome guest on farmlands. This plant is extremely resilient to water and light shortages and very difficult to remove for farmers. In cities, though, it creates beautiful wild lawns and - like nettle - has medicinal properties (it eliminates bacteria and relieves fever).

Ruderal plants have more than just medicinal properties. Most of them are wild ornamental plants, such as blossoming poppies, cornflowers or common chicory. They create beautiful, multicoloured collages, produce nectar and their striking colours attract various urban bugs. Weeds feed urban insects.

As third landscapes are covered with a number of different species, the total flowering time is very long.

This means that insects are provided for from early spring until autumn. When one species stops flowering, another begins, and this goes on throughout the growing season. Some of the wild plants are melliferous - they provide urban insects with the raw material to produce honey. Melliferous plants usually flower for an exceptionally long time, and their flowers are particularly rich in nectar.