Officials in Newport are on the look-out for a mystery gardener after cannabis plants were apparently spotted in council pots.
Around 30 of the illegal plants were photographed in the flower displays close to the city's castle and high street.
However, by the time council gardeners were told about the distinctive plants they had disappeared.
Steve Reynolds, who owns a shop in the indoor market, said he smelt the plants before he saw them.
"It was about a week ago we spotted them," he said.
"Walking into work I would see the council there with their vans watering the plants every morning, so the person who planted them also had the advantage of the council tending them."
Dean Beddis, the owner of Kriminal Records, managed to take photos of the plants before they disappeared.
Speaking to Sky News, he said: "It was the fact they were in the Newport Council official plant pots with the Newport logo on there.
"Where they were and what they were planted in was the funny aspect of it. It made us smile."
Newport City Council told Sky News it had been unable to find evidence of the plants.
It said: "The photographs provided appear to show mature plants added to a council planter.
"Although this could be a hoax, it is a serious issue and Newport City Council will be informing the police and checking its CCTV cameras for additional evidence."
Newport has won the prestigious Wales In Bloom competition seven times, but there are those who believe the council should be spending less time on the plants and more time trying to grow local business.
Some have suggested the cannabis plants may have been a stunt to embarrass council officials.
Gwent Police told Sky News: "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."