Blackburn magistrates heard that Iain Beardsworth had been growing the drug for his own use and had no idea that his son had somehow gained access to the locked garage.
Beardsworth (41), of Warwick Drive, Clitheroe, pleaded guilty to cultivating 53 cannabis plants. He was fined £500 and ordered to pay £60 costs.
Mr Neil White (prosecuting) said Beardsworth's son had taken some leaves from the plants to Ribblesdale High School Technology College and given some to his cousin.
"That was how the police became aware of the cultivation," said Mr White.
"They attended the defendant's home and asked him to unlock the detached garage where they found a sophisticated cultivation system."
Mr White said there were five substantial plants and 48 seedlings.
"There is no suggestion of him being involved in supply and it seems the son acquired the leaves without his father's knowledge."
Mr Daniel King (defending) said his client was a hard working, family man. "He is not keen on drinking alcohol and can't quite see the attraction of consuming a drug which causes people to act strangely and violently and cause a lot of anti-social behaviour," said Mr King.
"He has smoked cannabis resin privately and recently saw a television documentary which suggested that resin is not as harmless as had previously been thought.
"One of the reasons is that resin is adulterated with other substances in the production process."
"The fact hat his son got hold of these leaves brought it home to him that this is not acceptable," said Mr King.