Officers said on Tuesday they made the discovery following a tip-off from a walker.
A police spokesman said the size of the find was very unusual.
The 18,500 plants were growing in the woods near the village of Reuver on the Dutch side of the border. They were spread over an area measuring 5,600 m2.
It is not clear who the secret cannabis farm belonged to and no arrests have been made.
A special unit set about destroying the cannabis.
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