In an effort to bring a dash of green to gray concrete jungles, Catalan landscape artist Marc Grañén teamed up with green wall and roof designer Alex Puig.Grañén to perfect his Phytokinetic concept. Similar to the bus-top garden concept dreamed up by NYU graduate student Marco Castro Cosio, Phytokinetic is a mobile garden designed to be installed atop public transport vehicles.

Despite its apparent simplicity, there’s quite a bit of technology required to ensure the garden stays put and meets safety and transport regulations. A perforated stainless steel grid system anchors the plants in place in case of sudden braking and also helps the water circulate, while also allowing it to flow away so as to prevent it building up.

An ultra-light protective mesh can be added to enhance safety and prevent anything from moving or falling out of the perimeter. When completely fixed to the perimeter and the micro-perforated bands within, the entire planted surface becomes one unit welded to the structure of the bus. The designers claim that even if the bus turned upside down, everything would remain in place.

To waterproof the garden, an impermeable material called polyurea is sprayed on at 80° C (176° F). This material is ideal because it dries in just 10 seconds, and features high surface adhesion strength that allow it to withstand high tension levels.

Instead of using organic substrate, the design incorporates hydroponic foam, a material exclusively designed for adding lightness to roof gardens. With a thickness of just 7 cm (2.75 in), it can adapt to any surface, besides being easy to fit in either blanket or flaked forms. It’s also useful in preventing the evacuated water from getting mixed with earth and staining the bodywork of the vehicle. Being great at retaining humidity but not water, the hydroponic foam also helps keep weight in check during periods of persistent rain.

A plant carpet, which can be adapted to local flora, makes the entire planted surface green, adds a splash of color and prevents the hydroponic substrate from drying out. The air-conditioning units installed on the roof of the vehicle can also do the job of watering the plants. When it gets hotter and plants need more water, it's just a matter of turning up the air-con.

Last year, a Phytokinetic bus was displayed at the Iberflora exhibition and received the Best Sustainable Initiative award. Technical advice on how to comply with legal and safety regulations to help with the adaptation of roof-top gardens to the design and structure of different vehicles can be found on the Phytokinetic website.