Michael Petrie's backyard in Swarthmore is an exercise in what you could call surrealist gardening: A lawn ornament of upcycled glass bottles sprouts among flower beds, and a shed is wrapped in a mosaic of license plates, circuit boards, and pot lids.

But in late January, with the PHS Philadelphia Flower Show just a month away, the scene was shifting from eccentric to otherworldly. For instance, a 20-year-old pussy willow tree had been radically reconfigured, its branches twisted into a bird's nest of fantastical proportions.

It's all part of Petrie's singular approach to exhibiting at the Flower Show, which runs Saturday to March 13 at the Convention Center.

His process is slow and labor-intensive, surrounding foliage and flowers with objects found, foraged, or forged by hand - mostly by Petrie himself, in his own backyard.

"I've already spent hundreds of hours on this year's Flower Show and it's only January," said Petrie, 63, who is on his 36th Flower Show. "I've been to Oregon. I'm going to Florida. All those things take time."

This year, his challenge is compounded. He's perhaps the busiest man at the Flower Show, planning four exhibits: for his own landscape firm, Handmade Gardens; for show sponsors Bank of America and Tourism Ireland; and for the Men's Garden Club, of which he was a founding member.

By Tuesday, Petrie was navigating the show floor, checking on his progress. Volunteers and contractors pelted him with questions, about how to pile the composted sawdust used in place of dirt, where to place the sod, what to do with wayward tree trunks and unexpected spare parts. A volunteer wondered what to do about a grimy puddle that was flowing into the aisle, to the disdain of passing forklift drivers. She hesitated, but Petrie told her, "Never stop watering! We'll get a mop to come through here later."

Petrie, who worked for Styer Nurseries for decades before going into business for himself eight years ago, has built his business on the Flower Show.

"There's a lot of very slow return," he said.

The same goes for the objects and plants in his garden. It leaves room for serendipity: plant beds covered with pine straw instead of mulch allow seedlings to spontaneously take root, and flea-market finds wait for their true purpose to be revealed. (Sometimes, it never does. See the vintage trailer rusting in a corner of Petrie's yard. He admitted, "I tried to pitch it to Tourism Ireland: 'An Irish caravan?' Nah, a little too dicey.")

Still, all that flotsam comes together with planning. In his mosaiced garden shed, Petrie sorted through sheets of tracing paper depicting evolving designs for each Flower Show exhibit.

For Handmade Gardens, Petrie responded to this year's "Explore America" national parks theme with an homage to Olympic National Park in Washington. "I picked it because it's very green and serene - and it's something I can do without greenhouses," he said.

He wanted a design that would be relatable for potential clients. But how to connect a national park to home landscaping was a vexing riddle - until he spotted the solution driving down his street and parking in a neighbor's driveway. It was a partly completed tiny house on wheels. Serendipity.

"I thought it would make a great park ranger's office," he said.

Claudia Cueto and Tim Kearney - of CuetoKearney Design Architects - were building the prototype in advance of launching a tiny-house company.

"We're hoping to make a big splash at the Flower Show," Cueto said.

With the house at the center, Petrie planned a "West Coast modern" woodland retreat around it - rectangular beds of plants, moss, and gravel, with wooden decking and a fire pit amid a grove of cut trees and slab wood rescued from a sawmill. Hundreds of plants shipped in from Oregon fill out the landscape. Visitors, he hopes, will wander the perimeter of the garden like Peeping Toms.

"We don't want people to see everything all at once," he said.

By early this week, that forest hideaway was partially installed at the Convention Center, and Petrie's other exhibitions were progressing.

What were slabs of white Styrofoam stacked in his yard in January are now rocks carved with ancient inscriptions and piled in a rendition of the Irish monument Newgrange.

The tree-turned-nest - grown from a cutting from the Flower Show 20 years ago - had been cut down and erected as part of a Bank of America-sponsored exhibit showcasing the National Wildlife Federation's wildlife habitat certification program for home gardeners. Still due to arrive: a "meadow" of dried weeds and wildflowers Petrie harvested in November and dried to store through the winter.

"The challenge will be getting this to look natural, not like we faked it. Which we did," he said.

For the Men's Garden Club - which is evoking Congaree in South Carolina - he designed a series of bogs and boardwalks amid cypress trees and evergreens. The men of the club built the decking and railings. Petrie gathered 40 crates of moss last fall - from state game lands, he admitted - and kept it wet and chilled all winter so it would stay green. They had cypress knees shipped in, and will edge the blackwater bogs with moss and dust them with leaf debris to make them look authentic.

Still, Petrie can only do so much. "It's a swamp," he said with a shrug.

But Stan Amey, president of the garden club, said the men liked the idea of introducing attendees to a newer national park they might not have heard of. He knew Petrie was up for the challenge.

"He has a brilliant mind for conceptual things that he's able to then transform into actual gardens," Amey said.

By Tuesday, Petrie had about 20 volunteers helping him. He said he was thinking of cutting back to one or two exhibits next year. But, "there's economy of scale. It's the only reason why it works for me."

After all, whether the Flower Show stipend covers your cost as an exhibitor "depends how clever you are. Sometimes you have to go steal moss from the state game lands. I haven't been arrested yet. But it will make a great story when it happens."

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@samanthamelamed