Johnson used this week’s announcement to invite cash bids and said he wanted to plant up 40 residential areas that currently have few street trees.
The Mayor said he aimed to plant new street trees in every borough across London and would name more areas early next year.
“When I was elected I promised funding for 10,000 new street trees,” he said. “These are the first locations in London that will benefit.”
The 20 areas are in 15 boroughs and include:
Bromley by Bow
Successful locations in these areas will see between 100 and 400 new street trees over the Mayor's four-year term.
Bids are invited by 17 November from tree charities, councils and community groups.
Forestry Commission will work with environmental charity Groundwork London to manage the Street Trees programme.
Graham Simmonds, chief executive of Trees for Cities, said: “This will really help to transform some of our harshest streets.”
His charity has backed up the mayor’s campaign with its own, called Green Streets, which also aims to plant “thousands of street trees”.
Green Streets was launched by Neil Fox, the Magic 105.4 radio DJ, who is also the new patron of Trees for Cities.
Applications and bid guidance for the Street Trees programme are available from www.groundwork-london.org.uk/ltwgs.