Police found a large number of marijuana plants in Tamara Garlick's garden after a tipoff all she received for the crime was a warning letter.

A daily cannabis smoker has been let off with warning after police found 45 marijuana plants growing in her back garden.

Tamara Garlick's "surprising" punishment for cannabis cultivation - which carries a maximum penalty of seven years' jail - comes as politicians square off over drug reform in the run up to a binding referendum on personal use.

Commenting on the case, Greens spokeswoman for drug law reform, MP Chlöe Swarbrick, said she was aware the police already used their discretion when it came to prosecuting people for drugs, but it was far from universal.

"We want to avoid an ad hoc Russian Roulette when it comes to police responses to illicit substances," she said. Instead, they wanted a professional and just protocol developed to ensure people were "helped down a pathway of health rather than a pathway of criminality".

Garlick says she planted the summer crop in her back garden to save $375 per ounce through the year.

The 28-year-old dairy farm worker smokes a couple of times a day and before bed so she wanted to grow the plants for personal use. However, someone tipped off police and last Tuesday they removed her plants.

Garlick, who was at work at the time, expected the worst.

"Mum rang me and said I've had a lovely police officer here," the Ngāruawāhia resident told Stuff, "I was like, oh no, what? She said someone rang them and they've come and taken your plants. I asked what did they say and she said you need to go in and see them and they will give you a warning."

TOM LEE/STUFF Tamara Garlick planted 45 marijuana plants in her back garden to save her spending $375 per ounce.

Garlick doubted her punishment would stop there.

"It's not just a slap on the wrist," she recalled telling her boss, "I'm not going to be at work in the morning."

She thought about not going to the station but decided against that in light of the referendum.

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She was formally arrested at the police station and read her rights. She explained the cannabis was for personal use as she was sick of paying for it.

"The cop said ... I'm just going to give you a warning for it as you haven't been in trouble with us before, you are honest, you came forward, didn't make us chase you. I was like cool, sweet."

Garlick was surprised.

SUPPLIED Green MP Chlöe Swarbrick says they want a a professional and just protocol developed to ensure people were "helped down a pathway of health rather than a pathway of criminality".

"I thought I was done ... I knew it was my first offence and I would have used my diversion, hopefully."

Garlick was aware of the consequences of growing cannabis if she was caught.

She started using cannabis when she was about 16 years old after trying it at a party - she has been using daily for the past 10 years.

"I probably battle with a little bit of anxiety and things like that and I enjoy it, I enjoy being stoned. I enjoy doing things stoned.

"It makes me feel peaceful, calm, relaxed. If I am straight, I definitely don't chill as much, you can definitely tell the difference if I'm straight or not on it. I struggle to sleep at night if I don't have some before bed."

National's deputy leader and newly-minted drug reform spokesperson has also inhaled in the past.

"I was a girl in the 80s and grew up in Taupō," Paula Bennett told reporters this week, "and have tried it," .

Opposition leader Simon Bridges, who hasn't tried it, said the National party's new drug portfolio was intended to hold the Government to account ahead of a binding referendum on personal cannabis use at the 2020 general election.

"Let's learn from Brexit. Let's not have a simple yes, no thing, and then after that go through and answer all the complex, hard questions. Let's have that debate beforehand."

Bridges said he was likely to vote against legalisation. Bennett, too, said she was tempted to vote no.

"When it comes to legalising marijuana, there are serious questions around drug driving, the effects of younger people accessing and using, youth mental health, and how this fits with our ambitions to be smoke free," she said.

Swarbrick said the referendum, as committed to in the Green Party's Confidence and Supply Agreement, would will allow New Zealanders to have their say in creating legal regulation around cannabis.

TOM LEE/STUFF Tamara Garlick's smoking paraphenalia.

"We want to keep cannabis out of the hands of kids, and remove a revenue source for gangs that funds violence and criminal activity.

"We want to ensure that people can get access to help for addiction or substance abuse when they need it – which people won't ask for if they risk going away in handcuffs."

For Garlick, smoking has never had an adverse effect and she hasn't touched other drugs.

SIMON O'CONNOR/STUFF National's deputy leader and newly-minted drug reform spokesperson Paula Bennett recently admitted she'd also inhaled in the past.

She's hoping that cannabis is legalised. It would mean she wouldn't be breaking any laws by growing a couple of plants or buying it.

A police spokesperson said in a statement confirmed officers visited a residential address in Ngāruawāhia and found a number of small, immature cannabis plants. "Based on all the information available to police, and the explanation provided by the person involved, police deemed her suitable for a warning." The police approach to cannabis has not changed, the spokesperson said.