Who is called the father of modern American gardens?

Olmsted.

Olmsted is the leader of the landscape architecture trend after World War II, and is known as the father of American landscape architecture. He created the landscape around new york Central Park and the US Capitol.

Olmsted's works include Prospect Park in Brooklyn, Emerald Collar Park in Boston, Bilmo Manor in North Carolina, Mount Royal in Montreal, Parliament Square and White House Courtyard, as well as Washington Park and Jackson Park.