The study concluded that 5 minutes in a park was beneficial.
They found that the greatest health changes occurred in the young and the mentally ill, although people of all ages and social groups benefited. The largest positive effect on self-esteem came from a five-minute dose of "green exercise."The most positive effect came from green areas with water, but any park or grassy, green area will do... so if you've got one of those handy, walk around out there for 5 minutes, then come back an tell us if it worked.
Five minutes in the green can boost self esteem [Via Reuters]