To decide the party list, delegates draw up draft rankings and make a recommendation to the members. The members then determine the final list rankings. In the past, they have tended towards conservatism, placing sitting MPs highly even if they have not shone in Parliament.
This risk-averse approach was evident in the party's decision last night to pick sitting MP Denise Roche over Swarbrick to run in the Auckland Central seat. It is a crucial seat for the Greens because it is a rich source of party votes - they received more votes than Labour there in 2014.
But with Labour's Jacinda Ardern no longer running in Auckland Central, the selection of Roche could be viewed as a lost opportunity to put up a young, higher-profile candidate against National's Nikki Kaye. Swarbrick has momentum after placing third in the mayoral race despite no political experience, no budget, and no party backing.
There is now simmering discontent among some parts of the party about its members' preference for experienced but unremarkable candidates. Swarbrick openly challenging a sitting MP for the Auckland Central nomination hints at this discontent.
Her challenge created the possibility of a rare, embarrassing deselection, and suggests an orchestrated move by some members to unseat Roche or at least rattle the established MPs.
Two of the party's senior MPs, Catherine Delahunty and Steffan Browning, are leaving at the general election, but several others are staying on and on past form will get high list placings.
With six or more bright, young candidates on the list in 2017, the party could be more ruthless about giving them a shot at Parliament.