The ACT has become the first Australian jurisdiction to legalise the possession, use and cultivation of small amounts of cannabis.

Key points: Under laws passed on Wednesday, adults in the ACT will be able to grow two cannabis plants each

Under laws passed on Wednesday, adults in the ACT will be able to grow two cannabis plants each The laws say the plants cannot be grown in public or be accessible to children

The laws say the plants cannot be grown in public or be accessible to children They conflict with Commonwealth law, which does not allow personal cannabis use

The laws passed the ACT Legislative Assembly on Wednesday afternoon, allowing possession of up to 50 grams per person and a maximum of four plants per household.

They will come into effect from January 31, 2020.

The legislation conflicts with Commonwealth laws prohibiting the possession of cannabis.

And cannabis users have been warned there are still serious legal risks, including potential jail time, when growing or smoking cannabis in the ACT.

Cannabis remains a prohibited substance under Commonwealth law, and police officers in the ACT will retain the power to arrest and charge anyone with cannabis under those laws.

It will also be possible for the Commonwealth to overrule the ACT, and seek to have the laws struck out as inconsistent with its own legislation.

So what is allowed, and what isn't?

Any adult in the ACT will be able to grow two cannabis plants per person, with a maximum of four per household.

They will also be allowed to be in possession of up to 50 grams of dry cannabis, or 150 grams of wet cannabis.

Cultivating cannabis through a Canberra winter will not be easy though, as any Canberra gardener can attest.

Amendments suggested by the Greens to allow the cultivation of hydroponic cannabis were voted down, along with amendments providing greater allowances to those growing cannabis for medicinal purposes.

There also remain plenty of rules around when and where cannabis can be consumed.

It cannot be consumed in public, or anywhere near children, and will also have to be stored somewhere inaccessible to children.

Cannabis plants will have to be grown somewhere not accessible to the public.

It's legal under ACT law, but you may still be arrested

While now legal in the ACT, personal cannabis use is still a crime under Commonwealth law. ( Flickr: Nena B )

There is a very real chance consuming cannabis in the ACT could still put a person in handcuffs.

While speaking on the bill in the Legislative Assembly on Wednesday morning, ACT Attorney-General Gordon Ramsay made clear anyone growing or consuming cannabis was still carrying a degree of risk.

"This does not entirely remove the risk of people being arrested under Commonwealth law, and we are being up front with the community about that," he said.

"The ACT's legislation attempts to provide a clear and specific legal defence to an adult who possesses small amounts of cannabis in the ACT, but is prosecuted under Commonwealth law.

"But unfortunately it cannot stop someone being arrested and charged if the Commonwealth officials were minded to do so, or prosecuted if the Commonwealth Director of Public Prosecutions thought it were appropriate to do so."

The ACT Government sought the advice of Commonwealth prosecutors on the legal risk, and received a very strange response.

In one letter received last week, they were advised by Commonwealth Director of Public Prosecutions (CDPP) Sarah McNaughton SC that the ACT's laws would provide a defence to anyone charged under Commonwealth law.

And Ms McNaughton suggested that would be considered, before the CDPP went ahead with a prosecution.

But on Tuesday a second letter was received, fully rescinding that legal advice, apologising, and suggesting it was a matter with "legal complexities that had not initially been appreciated".

For their part, ACT Policing has indicated it understands the position of the ACT Government, and intends to respect it as best as it can.

Chief Police Officer Ray Johnson said they would continue to focus less on consumers of cannabis, and more on organised crime pushing large volumes of the drug.

"I'm not suggesting for one second that ACT Policing members are going to start a campaign of going out and charging everyone with Commonwealth offences," he said.

"I don't believe that to be the case, and I think for the most part our members understand what this debate is about, and will work with us to make it to best effect."

Unions have asked ACT Policing to be as upfront as they can with officers on how they should be making decisions, and have criticised the bill for putting officers in a difficult situation.

Is this a step towards commercialisation of the drug?

ACT Labor backbencher Michael Pettersson during the debate on cannabis legislation on Wednesday. ( ABC News: Jessica Brown )

The Labor MLA behind the bill, Michael Pettersson, indicated he saw some merit in the ACT eventually going down a path of commercialisation.

The crux of his argument was that if a person has a legal means of acquiring the drug, that would deliver a significant blow to organised crime — which currently has a near monopoly on its supply.

But this bill does not provide any kind of legal pathway to commercialisation.

Mr Pettersson told the Legislative Assembly on Wednesday morning that the major hurdle remains the Commonwealth.

"Some members of the community may wish this bill went further, such as establishing a market for the sale of small amounts of cannabis," he said.

"This would not be possible under current federal law, and has never been the purpose of this bill.

"This bill is simply about legalising cannabis for personal use."