Underground horticulture. Farm worker testing water quality at an experimental urban horticulture farm located 33 metres below the ground. The site, run by Growing Underground, is a disused tube tunnel in Clapham, London, UK. It uses coloured, energy efficient LED lighting and hydroponics (growing without soil) to produce crops throughout the year. This method of production uses 70% less water than open field farming and avoids the need for pesticides. Growing crops within an urban zone reduces 'food miles' compared to imported food crops.