Cannabis was reclassified from a class C to a class B drug in 2009. Dealers caught selling the drug can face up to 14 years in prison.
Possession of the drug can lead to anything from an £80 fine up to five years imprisonment.
Merseyside Police made 11 arrests and seized nearly 1,200 cannabis plants on the first day of a month long crackdown on cannabis growing.
Police have promised to weed out cannabis farms after more than 5,000 were discovered in north-west England.