A man with cannabis plants "riddled throughout his property" says they were a way of coping with grief after his partner died in the CTV building in the Christchurch earthquake, the Nelson District Court has heard.

Peter Wayne O'Connell, 55, pleaded guilty to cultivating cannabis after police uncovered "an extensive amount of cannabis" as part of a wider summer campaign to crack down on growers in the region.

Prosecutor Sergeant Chris Stringer told the Nelson District Court police completed a search on January 22 and recovered five plants of up to 1.5 metres tall along with others "riddled throughout his property".

As part of their national cannabis operation police flew over and spotted the plants at the address.

O'Connell explained to the police that they were only for medicinal use.

Defence lawyer Mark Dollimore said he wished to emphasise that police went out of their way to rule out the use of supply.

O'Connell suffered physical and emotional trauma relating to the fact his partner died in the CTV building in the Christchurch earthquake.

He had undergone counselling for his grief.

He was also due to undergo surgery on his leg and he also suffered extensive back pain.

"I know your honour hears this all the time but he [O'Connell] does not respond well to man-made medication."

But O'Connell promised to readdress the philosophy around the ills of cannabis consumption.

Judge Gregory Ross said O'Connell was effectively a first offender as his previous offences were "unrelated and many a years ago".

The offending as it stood was bad enough where the plants had reached full maturity and were "riddled throughout his property".

It was uncommon to see a defendant that did not "espouse the usual characteristics that came with the pro cannabis campaign".

The issues surrounding his health were compelling arguments, he said.

"May this be a lesson for you as to what is admissible and what is not."

He hoped O'Connell's operation was meaningful so that any future pain would not prompt any further cannabis use.

He was convicted and fined $500 with an order to destroy the plants.

While police have a year-round drug focus, the national cannabis operation officially runs until the end of April.