Greg Pierceall wants you to eat your veggies.

Pierceall, a professor of horticulture at the University, designed the system that allowed actual lettuce to grow out of a McDonald’s billboard, forming the words “Eat salad.” The billboard stood on the north side of Chicago for several weeks.

Pierceall said he was excited for the chance to work on the unusual project.

“I’ve always had the perspective that we could be doing things with ‘green’ billboards,” Pierceall said.

He incorporated the same species of lettuce used in McDonald’s salads but had to convince the advertisers to delay its construction.

Because the lettuce is 90 percent water, Pierceall said it “would never survive on a billboard in the middle of summer.”

The idea of trying to grow lettuce on the Chicago billboard was in question until its completion, said Regan Cronin, owner of one of the greenhouses where the lettuce was grown in Rockport, Ill.

“It was a little scary at first,” she said. “It was so hot and windy.”

The billboard was unveiled in late September at the corner of Clark and Addison streets in Wrigleyville. It has since been removed but not before attracting attention.

Peter Sheldon, a lecturer in advertising at the University, said that the distinct design mitigated its short lifespan.

“Go to Wrigleyville. Count billboards. How many would you notice?” Sheldon said. “Novelty draws you in.”

Pierceall’s project intrigued his students even though a four-month confidentiality agreement prevented him from discussing it on campus during his lectures.

“I thought it was really cool,” Cronin said, who is also a student of Pierceall’s. “We’ve been doing quite a bit of work on living walls.”

Pierceall’s inspiration for the vertical gardens or “living walls,” used on the billboard, came from the subject matter covered in his course titled “Residential Design.”

“I try to bring real-world experience into the classroom whenever possible,” Pierceall said.

Pierceall, an alumnus of the University, balances his time between University classrooms and teaching the Chicago-area horticulture degree completion program in Oakbrook, Ill.

He returned to the University after more than 30 years of experience in horticulture and landscape design.

“My roots were here,” Pierceall said.