Charles left for the United States shortly after playing a supporting role in his son's wedding. He delivered a serious 40-minute speech on sustainable agriculture at a conference organized by Washington Post Live.
"It certainly makes a change from making embarrassing speeches about my eldest son during wedding receptions," he told the audience at Georgetown University.
The prince had a meeting with President Obama. The White House said Obama congratulated Charles on Prince William's wedding to Catherine Middleton and thanked him for the work British forces have been doing in Afghanistan and Libya.
Obama was not invited to the wedding but is to make a state visit to London this month.
While Charles in his speech spoke of breaking agriculture's "umbilical dependence on oil," he arrived at Georgetown in a motorcade of seven vehicles.