The men, aged 49, 60 and 64, are charged with growing around 3.5 tonnes of the drug each year from 2004 until 2007, while in 2006 they harvested a bumper crop of four tonnes thanks to perfect weather conditions.
The men rented fields in North Rhine-Westphalia and Rhineland-Palatinate, hiding their cannabis crop by growing maize around the edges of the fields, a ruse which worked for years.
They also imported up to 30 kilos of other varieties from Holland each week, the court was told.
The drugs were sold to various dealers around Germany, while the three charged are also accused of selling smaller amounts of harder drugs.
A further man, aged 53, is also charged with acting as a middle-man, buying speed, ecstasy, heroin and cocaine for the gang.
A 31-year-old man was also in court on Wednesday, charged with selling around 360 kilos on behalf of the group.