The CityTree, which is 4 metres tall, 3 metres wide and 2 metres deep, is claimed to remove as much pollution as 275 trees.
CityTrees are made up of moss cultures, which have a much larger leaf surface area than any other plant, and can capture pollutants and remove dust and nitrogen dioxide from the air.
The vertical wall provides constant shade to the moss, and the installation powers itself via solar panels and rainwater is collected and automatically redistributed using a built-in irrigation system.
The CityTree also has built-in watering and ‘Internet of Things’ monitoring, which maintains and measures the performance of the living structure.
Each CityTree can remove around 240 tonnes of carbon dioxide every year, according to manufacturer estimates.
They require very little maintenance as solar panels power its electrical requirements and rainwater is collected for irrigation.
Elected Mayor of Watford, Peter Taylor, said: ‘I’m passionate about making our town more sustainable and so I’m delighted to be welcoming the town’s first ever pollution-stopping CityTree.
‘We will continue to look at how innovative and forward-thinking ideas can have a positive impact on the environment. These initiatives will help to improve air quality and reduce the use of plastic in Watford which is good news for all.’
A council spokesperson said there will be no cost to the council as the CityTree will be installed by a private housing developer.
London welcomed its first CityTree in March nearby to Picadilly Circus and two arrived in Glasgow during 2017.