Guerrilla gardeners at work in Calgary neighbourhood

Guerilla gardeners are flexing their green thumbs in northwest Calgary, along the Crowchild Trail noise barrier.

On a section of 24th Street, the sidewalk pavement gives way to a small plot of wildflowers and five pots of pink petunias.

"To me it makes the world a little bit more beautiful. Instead of concrete and weeds, you have flowers," said Ted Smith, who planted the roadside garden.

"There's nothing sophisticated about what I do. I just go for the most volume of colour, the most expansive greenery that I can get in the short growing season we have in Calgary," he said.

Smith has been tending flowers against the noise barrier for years, and says he has never heard from the city about it.

But there are rules about such things, and Smith does require a permit.

"It's not that the city doesn't appreciate the efforts, we just want to make sure that it doesn't interfere with anyone else's use of that area," said Kevin Leitch, a bylaw inspector.

However, the rogue garden has fans in the neighbourhood.

"I love urban surprises," says Richard White, the writer behind the Everyday Tourist blog.

He wants to see Smith's covert planting expanded on. He sees the noise wall as a blank canvas for neighbourhood gardeners.

"I could see that would be lovely with ivy growing up it, or hops or whatever. I mean I think it could be kind of a wonderful linear park."

Not far from the wildflower plot, a different kind of guerrilla gardening is happening. A big heart has been cut into the grass on a hill off 12th Avenue N.W.

That's a no-no, says Leitch.

"That's designated a natural area," he said, urging itchy green thumbs to leave their lawnmowers at home.

"They allow natural grasses and vegetation to grow for a number of different reasons, part of it is erosion and sediment control, water retention, weed control — keeping out invasive plants. It provides a habitat for birds and other animals."