Jeremy Corbyn has been nurturing a tree behind his house to plant in the Downing Street garden if he wins the election.
The Labour leader revealed the hornbeam - given to him by Extinction Rebellion protesters last month - as he launched his mammoth pledge to plant 2billion trees by 2040.
He defended the 190-tree-a-minute pledge by saying: "It’s not all going to be done by one person!"
But he is also doing his bit personally. Joined on stage by youth climate strikers, Labour's leader said: "We will be very very ambitious on this.
“And I will of course set an example by planting in the Downing Street garden.
“Indeed I’ve got a very nice hornbeam tree in a pot in my back garden, which I was given by climate extinction people when they demonstrated outside Parliament.
“I’ve been looking after it very very carefully and very very well, and I can find a really nice place to plant it.”
Mr Corbyn said "we are living in the jaws of a climate emergency" as he launched Labour's environment manifesto in Southampton.
The tree-planting would cost £2.5bn in Labour's first term - planting 300million trees - with targets to reach 1billion by 2030 and 2billion by 2040.
That is a rough average of 190 trees per minute, 24 hours a day, 365 days a year - from native woodlands to commercial forestry, including in Scotland and Wales.
Labour officials insisted the target was realistic, saying it would create 35,000 jobs, meaning each worker planted around 12.2 trees per day.
And Mr Corbyn told the Mirror: “Yes, it is a massive planting programme. I don’t apologise for that because it is a massive issue.
“And it is going to create good quality jobs. It will mean nurseries have to develop.”
He added: “The Forestry Commission established in 1919 was brilliant in its inception. But what it did was created vast forests of softwood fir trees that are actually not very biodiverse, not very sustainable and should have become much more mixed.
“In some ways the best thing that happened to them was the Great Storm of 1987 - a lot of natural species just generated in place of trees blown down in that storm.”
The plan comes after the Mirror this month launched a campaign to plant a million trees within five years.
Unveiling Labour's Plan For Nature, Mr Corbyn also vowed to double the 10 existing National Parks in England.
Malvern Hills, Chiltern Hills, Lincolnshire Wolds and North Pennines among candidates for 10 areas with a new 'National Nature Park' status in England.
The aim is by 2030, three quarters of all people in England will live within half an hour of a National Park or Area of Outstanding Natural Beauty.
Labour also warns privatisation of 2,000 miles of canals and rivers "has not been a great success".
The party would consult the public on returning waterways, canals and reservoirs could be returned to "transparent, accountable public management".
It would come alongside the nationalisations of rail, mail, energy, water and broadband - but a Labour source said public management is not the same as public ownership.
The Canals and River Trust look after waterways and are separate from private water firms. A Labour source said: "We will consult on how the functions of the Trust can be exercised in a more accountable and transparent way."
Ospreys, red kites and the Natterjack Toad would be reintroduced to parts of the UK, the fox hunting ban would be enforced while the "unnecessary" badger cull ends.
And an Environment Emergency Act would force public bodies to "act for the recovery of nature".
Mr Corbyn said: “Too often people are made to feel like the cost of saving the planet falls on them while the wealthy can fly about in private jets and heat their empty mansions.
"Well, we’re going to change that."
And he repeated his attack on the Tory government's US trade talks - in which Washington warned climate change could not be mentioned in a trade deal.
"I don’t care how sensitive it is," he said. "This is the biggest threat to our future.
“There could scarcely be more of a contrast between the complacency and denial of Trump and Johnson and the urgency of the younger generation whose future is at stake."
Looking to the young protesters behind him he said: “I’ve been deeply moved to see school children taking part in protests in the streets about climate breakdown... for someone of my generation it’s inspiring."