Defence lawyer Marcus Zintl said police would accept 40 plants as the basis of not being commercial.
"I will not sentence on the basis of no commerciality on the basis of 40 plants," Judge Garland replied, particularly when the growing system found at Keen's home could produce four crops a year.
"I would expect the police to prepare some expert evidence. The court needs to hear it and then consider, based on the facts."
Keen was entitled to withdraw his plea, but the judge said he was going to adjourn sentencing in the meantime.
"I know there is a view in the public arena that cannabis ought to be legalised. It is not and until it is I would hope the police prosecute a breach of the law. You don't have to be a rocket scientist to work out the figures here."
Judge Garland took issue with a 'dispute of facts' in submissions, claiming that Keen's activity was not commercial.
"The police have run with that. I disagree with that. Until that factual issue is resolved we don't get to where we are able to sentence."
Instead, he set a nominal sentencing date of January 12.
"I've recorded that I have declined to sentence on the basis that the cannabis was for personal use alone," the judge said.
Keen was found with 37 mature cannabis plants and 22 seedlings in a "sophisticated indoor growing operation".
Based on previous expert evidence before the courts, four crops a year could be grown in an operation such as Keen's.
"Based on the summary of facts, the total value of the cannabis is several thousand dollars," Judge Garland said.
But analysis suggested potential yield of the 37 plants to be between $4000 and $4700 each - "that is $148,000 to $266,400", the judge said from his own "quick analysis".
In addition, the 22 seedlings found in Keen's possession could have raised between $88,000 and $150,000 when mature - bringing the overall value of what was found to between $236,000 and $424,800.''
"I'm being told the police say this is for personal use ... It just seems unrealistic for the police to be putting this in front of the court on the present basis, and apparently police suggest they know it's for personal use.
"Why do police dish these cases up to the court seemingly accepting these are for personal use when clearly they are not?"
- Greymouth Star