NEW YORK — C.Z. Guest, a gardening columnist and fixture of New York society, died Saturday at her home in Old Westbury, N.Y. She was 83. An enthusiastic horsewoman, Guest began writing about gardening after being hurt in a riding accident in 1976. While recovering, she began giving friends advice about gardening over the phone and started writing columns for the New York Post in 1978. She also wrote several books, including "First Garden" (1987), with an introduction by her friend, author Truman Capote. As a writer, Guest was known for her plainspoken style and wide-ranging gardening expertise; she wrote...