Council officials in Newport are trying to discover who planted cannabis in flower pots put out to brighten up the city.
More than 20 of the illegal plants were discovered nestling amongst begonias and petunias in the street flower displays.
But by the time police were told and went to examine the specimens they had already been harvested.
The council said it was checking CCTV footage to find the culprits.
"I had never seen cannabis growing in the wild before so it was crazy to see it," said local businessman Dean Beddis, who made the discovery.
It's a serious issue and we will be
informing the police"
Newport council spokesperson
"It's actually rather a beautiful plant and stood out wonderfully. But they have gone now. I don't know who took them."
The leafy pot plants were growing in open view of passers-by on some of the city's busiest streets.
Newport councillor Rhys Hutchings, also a member of the band Goldie Lookin Chain, said he thought local teenagers were to blame.
"It's either kids or the Newport underworld community - I'm pretty sure it's not Alan Titchmarsh," he joked.
But city council officials have taken a dim view of the green-fingered criminals.
"It's a serious issue and we will be informing the police and checking our CCTV cameras," said a spokesperson.
Gwent Police said the fact that the plants had now gone was problematic.
"Now that the plants have apparently disappeared it's difficult to determine whether they were in fact illegal cannabis plants or not and, if so, whether they had been deliberately planted for cultivation," said a spokesperson.