About 120  cannabis plants worth an estimated £60,000 were discovered in a police search at Moneysharvin Road on Tuesday 19 October.
A detective said the discovery followed an arrest on Sunday.
He said a small amount of cannabis had been found by police carrying out a routine search of a car at Portstewart Road, Coleraine.
The 47-year-old driver was subsequently arrested.
In  a follow-up search near Maghera, a 22-year-old man was also arrested for possession of cannabis.
Police said the cannabis plants were found in three containers that had been dug into the ground.
Both men have been freed on bail as investigations continue.
Two men have been questioned about an underground cannabis factory in County Londonderry.