Market Square's inner courtyard is an oasis of calm in the heart of the city. No bleating horns or fume-spewing buses to intrude on a lazy summer afternoon.

Only the lilting sound of St. James Cathedral's carillon marks the time, as birds call from the canopies of eight-storey-high trees holding court on the second-floor roof of this downtown condo.

One can't help but envy the owners of the 100 or so units facing inward who covet this view, like a woman with a secret lover. Barely visible to outsiders, it's a two-decades-old gift that keeps on giving, a visionary, collaborative effort between Jerome Markson Architects, who assisted by Robert Ng.

"We came up with the idea there should be a garden there, before it was the thing to do," says Markson. "You don't want to see grey gravel every time you look out the window."

He is rightly proud the legacy continues, setting the tone for other city condos with "green" aspirations.

The courtyard, measuring 33,000 square feet, is shared by two adjacent nine-storey buildings and is perhaps the most mature and substantial "green" roof in the city, according to condo president Evan Merritt.

Consisting of both deciduous and coniferous trees, and a variety of plants and colourful flowers, it is thriving under the stewardship of Allan Kling, owner of Urban Garden Supply Co. Ltd., assisted by Market Square's volunteer garden committee, led by chair Susan McLeod.

Kling, who looks after about a dozen urban condos, "has such wonderful vision," she says.

Each tree has been mapped out and will eventually have a sign indicating its species. Kling says the courtyard could become an arboretum, providing not only pleasure, but educational value, too.

Some trees will have to be removed in future, when the building's membrane is replaced. Others will be lovingly moved by crane to be replanted later.

Among the former group will likely be Norway maples, which have large canopies that create too much shade, making it tough for plants to grow underneath.

Much of what's here has been chosen well, says Kling, and respects its environment.

Locust trees, for example, filter light so it penetrates to ground cover and they also aren't detrimental to the membrane. Japanese maples don't have a deep, penetrating root structure, either - which is good, because the soil is only about a metre deep.

Linden trees, columnar in shape, don't grow their branches out to rub against the building, eliminating the need for costly trimming, Kling explains.

White pines grow slowly and are also good long-term choices.

Rounding out the selection are cherry trees, white birch - lovely to look at in winter - and evergreens.

As for ground cover, Kling says the aim is to emphasize permanent cover and highlight tiny areas of colour, by using such flowers as begonias, which like shade, and ageratum, which has tiny purple flowers.

"Just add water and they'll flower all summer," he says.

Garden parties are held here twice a year.

McLeod says hardly a day goes by without someone telling her how lovely everything looks.

That includes the planters outside the three lobby entrances, which were less than satisfactory before Kling took over last year. They're composed of a profusion of colourful coleus, petunias, begonias, bacopas and hibiscus - all tough enough to take the heat. "You want bright, big, full and tough-as-nails'' types of flowers, Kling says. His mandate is to not only enhance the ambience for the residents, but to "make this building kind to the neighbourhood." He's done such a good job, the owner of the commercial portion of the building abutting St. James Lane has allowed Market Square to take on the responsibility for the laneway planters on a cost-sharing basis. That way, Kling says, there's a seamless continuity and no unfortunate contrasts between what each property exhibits. A bonus, he adds, is that "nice planters don't get vandalized as often as neglected ones do."

Atop each concierge desk inside the lobby, living floral arrangements have replaced cut flowers.

Kling starts the plants in his greenhouse, and then transfers them to pots, changing them about every two weeks.

It's much cheaper than having fresh flowers, and more attractive than having artificial ones.

On the southeast corner of the Front St. building, overlooking the courtyard and the city, is a large roof deck with barbecues, and an herb garden maintained by the garden committee. Residents are free to pluck the greens for their dinners.

Last year, the committee created an adopt-a-planter program. Residents buy plants and flowers and the condo provides water, soil material, fertilizer and tools.

The first year, about eight people participated.

This year, that number grew to 11. Some adopt more than one. Kling looks after the ones not yet spoken for.

Merritt says the program has been tremendously successful, helping to build community and also saving money.

People who had to give up gardening when they moved to a condo now can keep a hand in it.

(Indeed, Merritt says, the program may be expanded to include parts of the courtyard.)

Grethe Nielsen, a real estate agent with Re/Max Professionals Inc. who lives at Market Square, says she can't count the number of deals she has signed on the roof deck.

"It's become my summer office," she says.

She often brings clients there at dinnertime, making introductions to residents using the patio, standing back and "watching the magic happen." She's seen many friendships blossom this way, she says.

When they look over the wall, to see the courtyard below, she loves to watch the looks on their faces.

"They have no idea there's an oasis in the centre of Toronto," she says.

She admits to tricking one couple into viewing a unit by saying she had to stop by her home to pick up paperwork.

The couple had firmly stated they wanted to look for a mid-town condo.

She brought them to a suite facing the inner courtyard and they instantly fell in love.

They walked in and said, "That's it"