To kill a cannabis plant:
Take one pair of poultry shears- the ones you bought from the Cutco guy last decade will work perfectly.
Place them at the base of the plant.
Now, squeeze the handles until the plant falls over.

Please tell me you aren't trying to kill someone ELSES plants and make it look like THEY did it by mistake?

By the way, your avatar violates TWO site rules (showing other drugs or large sums of money in pics) and needs to be removed. Thanks.