Philip Bevington, of Camborne, admitted two counts of cultivating cannabis at Truro Crown Court.
He told police they were for medicinal purposes to alleviate pain from kidney failure, after being caught by officers twice in two months.
Bevington was sentenced to a two-year conditional discharge by Judge Simon Carr, who ordered the drugs destroyed.
Officers went to Bevington’s home to investigate a “strong smell of cannabis” in November 2019, the court heard.
The 80-year-old showed them a sophisticated hydroponic growing set up in his garage housing 30 plants, including a ventilation system, lamps hanging from his ceiling and plastic sheets lining the walls.
These plants had the potential to grow three crops a year, which would have had a street selling value of £12,600 to £37,800, the court was told.
The same police officers returned two months later in January 2020 and found 44 plants.
Judge Simon Carr acknowledged Bevington was growing the cannabis for his “own personal use to alleviate pain”, while suffering from his condition and mobility issues, which left him housebound.