In this election year, and with the Independence Day holiday just past, we have something of a patriotic garden theme going. This week, we’re joined by Marta McDowell, a gardener, historian and writer who lives in Chatham, New Jersey. Her self-described greatest interest lies in the relationship between writers and their gardens — the connection, as she says, “between pen and trowel.” This interest is well-illustrated and developed in her titles to date including “Emily Dickinson’s Gardens,” “Beatrix Potter’s Gardening Life,” and most recently the patriotic history of the White House Gardens entitled: “All the Presidents’ Gardens” out now from Timber Press, and the focus of our conversation.