A disused council leisure centre in Newport was bought and turned into a cannabis farm worth up to £1.6m.
Mohammed Nawaz allowed drug dealers to use buildings he owned across Britain, Cardiff Crown Court heard.
One was Underwood Leisure Centre which he leased to Abdul Manuf, 46.
Nawaz, 68, of Stoke on Trent, was jailed for seven years and Manuf, of Edgware, London, for three years and one month for conspiracy to produce a controlled drug of class B.
Underwood Leisure Centre was sold for £82,000 at auction in February 2014.
Six months later, in August 2014, police found more than 2,600 plants in the former gym and badminton hall.
The drugs were being grown at an “industrial scale” with a yield of 132kg – potentially worth up to £1.6m.
Manuf used the cover of working as a taxi driver to ferry drug dealers between the properties but denied knowing they were being used to grow cannabis.
The court heard when Nawaz became aware police wanted to search the properties, he notified them himself to try and cover up his involvement.
Nawaz was found guilty after trial but Manuf admitted the charge.
Judge Neil Bidder QC said: “Greed was a strong motivation for you and you allowed criminals to use your premises to grow cannabis.”
After the case, Iwan Jenkins, of the Crown Prosecution Service, said: “These two men were involved in the illegal drugs business, whether they actually grew the plants or not, and have now been dealt with for their criminal activities.”