If you’re looking for a more traditional way to celebrate St. Patrick’s Day—more traditional than, say, drinking with abandon—there’s always the Planting of the Shamrocks ceremony. The custom has its roots in the 19th century, when George Washington Parke Custis, Robert E. Lee’s father-in-law, was an ardent supporter of Irish independence. So grateful were the Celts that an Irish contingent shows its appreciation each year by planting clover on Custis’ grave. Today’s holiday open house includes Celtic music, speakers from the Hibernia Society and the Irish Embassy, and a bagpipe procession. From 1-4 p.m. at Arlington House, Arlington Cemetery. FREE. (703) 557-0613. (Maria Ware)