The issue of sustainability has been championed by the King since 1970.
The King toured an after-school, urban farming effort that works with young people affected by food insecurity.
At Harlem Grown's 134th Street Farm, Charles planted lavender and mustard seeds with primary school children and visited a chicken coop. He watched a live food demonstration that educated children about food and nutrition while showcasing vegetables harvested at the farm.
"I like your hair," a student told the king, who replied, "Do you? Good."
Charles even fed the chickens.
He addressed the complex issue of food insecurity, often referring to farmers as custodians of our land.
Charles has visited Harlem before, but this was his first as Monarch.
Epiphany Adams had the honor of telling the King all about what happens at Harlem Grown. The 24-year-old is the first student and graduate of the program.
"He wanted to come here, like he's talking to Congress, he has other things to do with the trust and he's like no, I want to come here, I want to learn about farming, see how it's done and like for me when I heard that it went from him being King Charles to just Charles," Adams said.
The queen, meanwhile, visited the New York Public Library, where she chatted quietly with actress Sarah Jessica Parker during a walk in the building as a massive crowd of onlookers watched from behind barricades across Fifth Avenue.
Camilla was to deliver a new Roo doll to add to the library's famed collection of Winnie-the-Pooh stuffed animals, as the beloved children's character turns 100 this year.
The five dolls currently on display - Winnie-the-Pooh, Piglet, Tigger, Eeyore and Kanga - were the inspiration for the characters in A.A. Milne's children's books. They were owned by the English author's son, the real-life Christopher Robin, in the 1920s. The dolls were donated to the library in 1987 and are a centerpiece of the library's collection of children's literature. Roo, in the books, was a small brown kangaroo and the son of Kanga.
The royal couple was then expected to attend a reception for the King's Trust, a charity Charles founded in 1976.
The four-day trip is Charles' first state visit to the U.S. since he became king. His mother, Queen Elizabeth II, made four state visits to the U.S.