Mark Storey, 54, started the event with his friends after asking respondents in a poll what they enjoy doing naked, the New York Daily News reported.
Swimming was the No. 1 response, but gardening came in at No. 2.
So Storey, of Seattle, decided to set aside May 4 to encourage people to exercise and connect with nature while naked, he said.
"The gardening-naked connection is pretty natural," he said. "There's not much body acceptance around, so the idea is to get people to try it. Maybe they will realize that the human body is OK, and also beautify the Earth a little bit."
There wasn't a large gathering for the event, which was held Saturday. Instead, gardeners celebrate it all over the country in their own way, the Daily News said.
"It could be a little old lady in downtown Chicago with a potted plant, or a group raking leaves at a nudist club," he said.