Labour leader Jeremy Corbyn and Liberal Democrat chief Tim Farron are on the "wrong side of history" at the general election, Jonathan Bartley has claimed.
"I am extremely disappointed with the way that the Labour leader and the Liberal Democrat leader have responded," Bartley said.
"Our first priority when the general election was called was to write to them both and say 'come and talk'. They didn't even come and talk, that's really disappointing."
He added: "Things are changing. There are politicians who get that things are changing and will be on the right side of history and there are politicians who don't get it and will resist it – they will be on the wrong side of history. But what is great is that at the grassroots people are defying their leaders."
Bartley pointed to the success of the Richmond Park by-election in December 2016, where the Greens stood aside and endorsed the successful campaign of Liberal Democrat Sarah Olney to unseat former Conservative MP Zac Goldsmith.
The Liberal Democrats have also decided not to contest Brighton Pavilion at the general election. Bartley's fellow co-leader Caroline Lucas is hoping to defend her more than 7,900 vote majority against Labour in the coastal constituency.
Liberal Democrat grandee Sir Vince Cable, the former business secretary, has also urged his party's activists to vote tactically for Labour candidates at the general election. "The tectonic plates [of British politics] aren't just shifting, they are breaking apart," Bartley said. "It's not just Britain, it's a global phenomenon."
Elsewhere, the Green co-leader revealed that he was able to win a concession from the BBC after protesting about the amount of airtime Ukip were given on the broadcaster.
"I will now be doing a half-an-hour debate on 4 June. They have given us that, I don't think it goes far enough, and since then we now know we will be fielding many more candidates than Ukip at this election," Bartley said.
"It does seem that Ukip are an absolute spent force. For them to be getting this amount of press coverage is frankly an insult to everyone."
With just over three weeks before the election, the latest Kantar poll, of more than 1,200 people between 11 and 15 May, put the Greens on 4%, just below the party's vote share performance (3.8%) at the 2015 general election.