The National Arboretum offers several programs: The history of the cherry blossom will be discussed during an April 16 talk. At 10 a.m., join author Ann McClellan as she details her book, "The Cherry Blossom Festival : Sakura Celebration," (Bunker Hill Pub., $19.95) exploring the history, significance and anecdotes of the trees. 3501 New York Ave. NE. Fee: $7, registration required. 202-245-4523. Hundreds of camellia blooms can be seen this weekend during the Camellia Society of the Potomac Valley's annual show. Open Saturday, 1 p.m. to 5 p.m.; and Sunday, noon to 4:30 p.m., in the Administration Building. 3501 New York Ave. NE. Free. 202-245-5898. A tour of Fern Valley on April 15 at 10:30 a.m. offers the sights and smells of native plants. Free. 202-245-4523. www.usna.usda.gov . . . Belvedere Plantation's Flower and Garden Festival is open tomorrow, 9 a.m. to 6 p.m.; Saturday, 9 a.m. to 6 p.m.; and Sunday, 10 a.m. to 4 p.m. Fee: $7; kids 12 and under, free. 540-899-4020 ext. 24. www.ext.vt.edu . . . "Integrating Roses Into Your Garden" is the theme of a Monday talk sponsored by the Arlington Rose Foundation. At 7:30 p.m. in the Merrifield Garden Center's Fair Oaks location. 12101 Lee Highway, Fairfax. Free. 703-860-0071. . . . From 1 to 2:30 p.m., landscape designer and author Sandy Austin ("Color in Garden Design," Taunton Press, $34.95) discusses perennial combinations and explains why they work at tomorrow's lecture at Green Spring Gardens Park. 4603 Green Spring Rd., Alexandria. Fee: $15, reservations required. 703-642-5173. www.greenspring.org. . . . A spring seed and plant exchange will be held Sunday at the Eastern Loudoun Regional Library. At 2 p.m., participants are invited to bring seeds, houseplants, herbs and perennials for exchange. No money will change hands. 21030 Whitfield Place, Sterling. 703-430-2136.