He makes sure the plants travel safely to a new home, in a far less glamorous part of the city.
At Riker's Island prison, inmates tend to the shrubs.
"We're trying to bring in nature onto Riker's Island and have our inmates, our students, be part of that human nature interaction," says Jiler.
Jiler is a one-time Wall Street commodities analyst who dropped out of the fast lane to study urban ecology. He was hired by The Horticultural Society of New York to direct The Greenhouse Project. It's a $215,000-a-year program designed to rehabilitate convicts, even though that's out of fashion in many prison systems.
"People generally are going to be released, and they're going to be part of the community once again," says Jiler. "Why are you returning people to the community angry, bitter, resentful and anti-social? Because, they're going to commit crimes once again and you may be part of that crime. It's much better to send people home with a skill."
At Riker's Island, Ismaela Miranda and her friend, Sandra Clemens, are both imprisoned for drug violations. Clemens is finishing up her sentence, but Miranda is only three weeks into her 8-month term.
"There's so much out there besides doing drugs," says Miranda. "I have twins and I have a 19-year-old, and they're rooting for me … So, I don't want to let them down."
Miranda and Clemens were just starting to work on an unplanted, scruffy patch of garden when CBS News Sunday Morning met them. But don't let the idyllic scene fool you. The garden is surrounded by barbed wire. Prison guards conduct security checks. Women prisoners are never allowed in the garden at the same time as the men, who are also part of The Greenhouse Project.
About 125 inmates are cycled through the program each year. There's a waiting list to get in. Most of those chosen are non-violent offenders, such as Mario Moreno, in prison for dealing drugs.
"It's a chance to get outside of the environment that we're in on a regular basis," says Moreno. "The time I spent in here gave me time to reflect upon how I was making my money, and gave me time to think about all the avenues that I have to attempt when I get out of here."
Moreno says he was a good person before he started selling drugs. He says he wants a chance to be a "good guy" again.
But turning the prisoners into good guys is hard work. James Jiler says this program is different from traditional prison farm labor, which is usually seen as punishment. Along with lessons in gardening and skills, such as woodworking, to build planters and flower boxes, inmates get job counseling from Jiler and his partner, John Cannizzo.
"People just aren't out there doing work," says Jiler. "They're actually learning why they're doing what it is they're doing. And more important, we worry about what happens to them once they're released."
In fact, one of the most innovative aspects of The Greenhouse Project is that prisoners can keep gardening when they get out, for pay. Workers loading plants at Rockefeller Center are part of the Green Team — ex-cons who now earn $7 to $10 an hour.
The workers bring plants to Riker's Island and schools, such as Joseph Lanzetta in Harlem. There, ex-cons helped create a rooftop garden, even bringing in planters constructed at the prison.
"I'd like to go to Riker's Island and watch these guys put this together and tell them, 'You know what, the stuff that you made, it's in my school, man! It's in my school. My kids are planting in this stuff. Thank you. Thank you for beautifying a school. And thank you for being part of a child's life,'" says Principal Victor Lopez.
After six years in existence, the program has a small rate of repeat offenders — 5 to 10 percent, compared to 65 percent in the general population. Some Greenhouse Project alumni find permanent jobs with landscaping companies. Others go on to different fields. But there are plenty of sad stories.
One prisoner was considered a sure bet to make it on the outside. He left Riker's Island with a great job, restoring an old house. But a year and a half later, he was back into drugs and back in prison.
"It breaks my heart. It really does, because I measure the success of what we do out here based on, you know, changing peoples lives," says Jiler.
Miranda says having a person, such as Jiler, does help her believe in herself.
"If somebody believes in you, it gives you a little bit more hope," says Miranda. "If they can believe in me, why can't I believe in me? So it matters a lot."
Recently, Jiler and the Green Team helped put a garden at the Walt Whitman Library in Brooklyn. Mario Moreno, the former drug dealer, was out of jail and working alongside the team. Moreno says he hopes before long to find a permanent job in his former field of nursing.
"The opportunity to do illegal crime is just, it's abundant. It's everywhere I live," explains Moreno. "So if I hadn't turn my life around, I would have already went back to doing negative things. And I haven't."
Ismaela Miranda was out of jail, working with the Green Team ,too.
"It keeps me busy," says Miranda. "I need it. I got to pay my rent. I got to eat. I got to buy my kids clothes and stull like that. And myself clothes. I'm a regular citizen that pays her dues in life."
She's a regular citizen with big dreams.