A farmer with land between Grantham and Sleaford called the police after coming across a cannabis plant.
Officers say that three patches of grass, each measuring a metre squared, were cut out, cannabis planted and green chicken wire placed around them.
The plants measured seven feet in height.
A police spokesman said: “It is expected that farms with shoots upon them may well come across such grows in the next few months. However it is requested that staff, farm workers, beaters and family are warned to keep an eye open at all times and report anything that they think is suspicious to the local police.”
He added that no action would be taken against people who report finds.