On Dec. 5, 11 a.m. or Dec. 10, 2 p.m., Dr. Susan Pell, US Botanic Gardens deputy executive director, conducts a tour of Season’s Greenings: America’s Gardens to learn more about plants included in the holiday exhibit. Discover which leaves, stems, flowers and fruits are used to create plant-based recreations of DC landmarks. Use a magnifying glass to investigate the tiny flowers of a poinsettia or learn about the scents of evergreen trees. Free but registration is required. usbg.gov.