A Dutch initiative to combat illegal cannabis cultivation through the use of marijuana-scented 'scratch-and-sniff' cards that has gone nationwide can now alert citizens to what their neighbours may be up to.
The expansion comes after a pilot project launched three years ago to combat illegal weed plantations by helping people to recognise the smell proved a success.
Backed by police, city councils and energy service providers who have their electricity stolen, thousands of cannabis-odoured cards will be distributed in four Dutch cities including Amstelveen near Amsterdam, a spokesman for the initiative said.
"The cards are being made available across the country, starting with the four cities this week," Martijn Boelhouwer told AFP. "We hope other cities will follow."
Boelhouwer said since the cards were introduced in The Hague and Rotterdam, the number of reported plantations has "gone up enormously", with one call to police a day in each city.
The proportion of people able to sniff out an illegal plantation increased from 40 to 60 percent, Dutch daily Trouw reported.
The Netherlands is known for its expertise in hydroponic cultivation and the growing of illegal cannabis is no exception.
There are an estimated 30,000 illegal cannabis nurseries in the Netherlands, with plantations often set up in attics, cellars, garages and even entire houses.
Police estimate the bulk cultivation and sale of cannabis was worth some 2.2 billion euros in 2012, most of it in the hands of criminal organisations.
"With this cannabis-scented card you will recognise the smell of marijuana cultivation. Scratch, sniff and help," reads the text on the green scratch-card, which lists a police telephone number.
Illicit cannabis cultivation is dangerous because of the fire-risk created by illegal electricity connections and faulty wiring, Boelhouwer told AFP.
"At least 20 percent of all industrial fires are caused by illegal marijuana cultivation," added Danielle Nicolaas, spokeswoman for energy company Stedin, which forms part of the project.
Illegal power connections also tapped some 200 million euros ($270 million) in stolen electricity from service providers every year.
Though it remains technically illegal, the Netherlands decriminalised the consumption and possession of under five grammes (0.18 ounces) of cannabis in 1976 under a "tolerance" policy.
Authorities turn a blind eye to citizens growing no more than five plants for personal use, though that too is illegal.
Last year police rolled up 5,800 nurseries, according to the latest police statistics.