For artist Patrick Dougherty, mistakes are always happy accidents.

The sculptor works with natural elements to create grand, site-specific sculptures. For three weeks, Dougherty set up camp at the Morris Arboretum to create A Waltz in the Woods from willow branches. "It's a smooth waltz where these little towers use this meadow to celebrate," he said.

Morris will mark the debut of Dougherty's most recent work with a grand-opening event Saturday, including a guided sculpture tour and a craft event for kids. Depending on weather, the sculpture should be up for one to two years.

Dougherty previously visited the Morris Arboretum in 2009 for his project Summer Palace.

Dougherty said there was only so much planning that could take place before construction actually started. "You can always think of something in one minute," he said, "that can fill a lifetime of work."

To create a successful piece, Dougherty says, he must "maximize the accidents," lean into "the serendipitous, and truly ride the opportunities that lead to great work."

A Waltz in the Woods consists of seven towers around the space that Summer Palace, a piece Dougherty calls one of his better works, inhabited in 2009. The three-week construction process employed 25 to 40 volunteers from the staff of the Morris Arboretum. The towers themselves are made out of willow trees from a farm in Fredonia, N.Y.

The work seems to twist up to the sky.

"These little towers are in a baroque frame of mind," Dougherty said in his North Carolina lilt. "They've got gesture, they don't look stiff. They look a bit like bodies in motion."

That sense of movement is one of the reasons Dougherty is drawn to working with natural materials.

"There's a fragility about the natural world. There's a tree that's particularly powerful, but it needs to be fostered. There's a vulnerability, and these sculptures have that vulnerability," Dougherty said. "The small twigs come together to gain mass and momentum."

But Dougherty, who has completed more than 250 site-specific sculptures over the last three decades, is also drawn to the notion that each project is rooted in its here-and-now, one place, one time only.

"Early on, I thought I should just go ahead and do the work I wanted," he said, "because it was a presumptuous to think I would be remembered in 20 years, to think I was the Michelangelo of my time."

That one-time-only quality "put the emphasis back on the work," he says. "These pieces can't accrue value. It's all about what it offers to the viewer that comes to see it. You can see pictures, but coming to see it, there are smells, different views. It is a full-body experience."

Guided Sculpture Tour, 11 a.m. & 2 p.m.; Kids crafts, 11 a.m.-3 p.m.; Sculpture Scavenger Hunt, debuts Saturday and continues through October. Morris Arboretum, 100 E Northwestern Ave. Kids (3-17 years), students, active and retired military (must have ID): $8.00; seniors: $14; adults: $16. Information: 215-247-5777

215-854-5909

@mollyeichel