In areas where pot is illegal, then yes, police should go after this and stop it. There is no use having laws if they are not enforced. In my experience and opinion, pot leads to other, more dangerous drug usage, and it also goes hand in hand with crime. I also don't think it's safe for young people especially.
There are states which are yet to legalize pot and in such state police are very much in order to are arrest the pot growers. Residents in such states should petition their legislative arm of state government to legalize marijuana. Scientist have proved that weed has medicinal though the intake of the same should be controlled.
Pot is the least of anyone's concerns anymore. It would be great to see the stuff legalized nationwide, as it would results in such great things! We would see a huge budget overage, bringing in millions or even billions of dollars in tax revenue. We would also see less people involved in illegal drug trade, which is very dangerous. Just let the pot heads be pot heads. There are more important things to worry about.
It depends on what the location of the pot is. If it is in a state where pot has been legalized, then the police have no right to seize the pot plants. If it is being grown where pot is still illegal, then the police are well within their rights to seize the plants.