Status: This statement has not been found in any of the writings of Thomas Jefferson. It appears to be of extremely recent vintage (first noticed online in 2008), and only made its way into print sources as of 2013.1
Thomas Jefferson did grow hemp, but there is no evidence to suggest that Jefferson was a habitual smoker of hemp, tobacco, or any other substance. Some have pointed to a supposed reference in Jefferson's farm book to separating male and female hemp plants as evidence that he was cultivating it for purposes of recreational smoking; no such reference exists in Jefferson's farm book or any other document.
George Washington did record the practice of separating hemp in his own diary: "Began to seperate the Male from the Female hemp at Do.&—rather too late."2 Arthur Young, well-known English agricultural writer, explained the separation of hemp as follows: "This may arise from their [the male] hemp being coarser, and the stalks larger."3