A 73-year-old Tasmanian man who grew cannabis for his son to strengthen their relationship has been convicted of drug trafficking.

When police searched Charles Patrick Hay's property in New Norfolk in September 2016, they found four mature cannabis plants and 19 seedlings.

Police also found 30 bags of cannabis weighing between 28 grams and 64 grams.

A Supreme Court jury found Hay guilty of trafficking in a controlled substance and cultivating a controlled plant for sale.

The court heard it was Hay's third crop but that he had not been selling the drug himself.

Instead, he had been growing the cannabis with his son in a bid to strengthen his relationship with him.

The court heard his son had given him between $600 and $700 to cover the cost of the electricity to run the hydroponic system used to grow the cannabis.

Justice Gregory Geason accepted that Hay did not himself profit from the crimes, and noted he had cooperated with police.

"I accept that the arrangement came about as a result of your desire to strengthen your relationship with your son. I consider that that motivation was misguided, but understandable," Justice Geason said.

"You live alone and it may be that the arrangement meant you had more contact with your son than might otherwise have been the case."

The judge took into account Hay's lack of prior convictions, motivation for offending, age, financial circumstances and remorse.

He sentenced Hay to two months' jail but wholly suspended it on the condition he commit no further offences for three years.

"The principles of general deterrence require that I impose a sentence which deters others from acting as you have," Justice Geason said.

"Whilst some take the view that cannabis does not represent a social problem, it is illegal. The court has an obligation to uphold the law. You have an obligation to abide by the law."

Justice Geason said drug trafficking caused a lot of harm in the community and Hay had contributed to that, but that he doubted Hay would commit the crime again.

He said "the need for personal deterrence in this case is not significant".