In the UK, more than 80% of people live in urban areas (Defra, 2004), though the greater growth is now in rural areas. Urban settings by definition have less nature than rural ones. And less green nature means reduced mental well-being, or at least less opportunity to recover from mental stress. The World Health Organisation estimates that depression and depression-related illness will become the greatest source of ill-health by 2020. This is partly because some other behaviours, such as smoking, over-eating and high alcohol consumption, are likely to be coping mechanisms for mental ill-health and stress, and have their own serious consequences.