Green Party leader James Shaw addresses the media after NZ First sides with the Labour Party.

Incoming Prime Minister Jacinda Ardern will work with her Cabinet and take advice before holding a referendum on legalising recreational cannabis.

She said her Executive would decide when the referendum went ahead and was personally open to the discussion. Ardern said there was a need to balance overly harsh criminal sentencing with the drug's capability to cause harm.

"During the campaign I've always been very vocal about the fact that I do not believe people should be imprisoned for the personal use of cannabis. On the flip-side, I also have concerns around young people accessing a product which can clearly do harm and damage to them," she said.

GRANT MATTHEW/STUFF The Greens appear to have fought for and won the right to hold a referendum over the legalisation of cannabis for personal use.

Ardern made the comments during a press conference to unveil the members of her party who would eventually get ministerial portfolios.

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Earlier, an internal Green Party email revealed a raft of policy concessions for the Greens in Government, including a referendum on the full legalisation of the personal use of cannabis.

Ardern said she would look for a way through the debate, gauge the mood of the public and look "to find a workable solution".

A "justice-based" approach to cannabis was not working. The Green Party email suggested the parties would move more rapidly to a health-based approach.

The Labour Party also appears to have promised a major increase in the Conservation budget, huge bumps to funding across social issues and an overhaul of the welfare system - a policy former co-leader Metiria Turei bet on and lost her job over.

ROSS GIBLIN/STUFF Greens leader James Shaw has also secured an increase in the conservation budget and an overhaul of the welfare system.

In the email to members, it was also revealed the Greens were expecting stronger laws to regulate and improve the quality of water and the wind-down of government funding for irrigation.

"Our Government will treat all people with dignity and respect. We will insulate more homes and bring home ownership within reach of more people," the email said.

"We will help fix the mental health system. And our education system will better support all children, no matter what their learning needs are."

The party leadership has also moved to prepare its members for some difficult conversations as part of a government with Labour and NZ First.

"Governing with Labour and NZ First will mean sometimes we'll have to be pragmatic. We share a lot of goals and values, but not all of them."

The email does not reveal the finer policy points that have been negotiated - the agreement between Labour and the Greens is expected to be released some time next week.

But leader James Shaw said it was an ambitious programme of work that had been bargained, and some of the policy gains they were expecting would be outside of the portfolios the Greens could expect to hold.

Conservative lobby group Family First was already preparing to rail against the prospect of a referendum. National director Bob McCroskrie said it would be running a "nope to dope" campaign.

"Legalising marijuana and the rise of Big Marijuana is the wrong path if we care about public health, public safety, and about our young people.

There are too many health risks including the effect of marijuana on cognitive ability, cardiac function and psychosis," he said.

GREENS' POLICY GAINS:

* Significant climate action with a shift to a net-zero carbon emissions economy by 2050 (specific focuses will be on transport, energy and primary industries).

* The establishment of an independent climate commission.

* Support for a shift in farming to more sustainable land use.

* Overhaul of the welfare system, removing "excessive sanctions" and a review of Working for Families.

* Increase to conservation budget.

* New water quality measures.

* Free counselling for under-25s and access to mental health services and support for everyone.

* Special needs education access.

* Progress to end gender pay gap in public service.

- A reduction in number of students living in hardship.

- Increase in funding for drug and alcohol addictions services and a referendum on the personal use of cannabis by the 2020 election.