During the summer, the world is your table — and dining alfresco means spreading a blanket over the plush green grass and producing a buffet of delicacies from your charming wicker basket. (Or pulling premade sandwiches out of a plastic bag, and commandeering the best-shaded picnic table from those kids who just ran off to chase a Frisbee.) Here are six spots throughout the region where you can partake in picnic season, including a hidden gem along the C&O Canal and a fairy-tale like garden tucked away in the city. There are a few designated picnic spots at the colorful, sprawling National Arboretum, a 446-acre property in Northeast Washington that feels like the District’s answer to Central Park. Head to the shaded tables that are just a short walk from the National Capitol Columns — wandering around is encouraged, but there’s a parking lot next to the picnic area for quick access, too. There are also a few tables behind the Arbor House, says Scott Aker, head of horticulture and education. Another set of tables is expected to return to the Visitor Center area this summer. Aker notes that guests can’t barbecue or bring alcohol, and there’s no way to reserve space in advance....