I never heard that a beer garden was scheduled. There is a nice beer wagon located over in the Paradise Pier area, as well as the Margarita place like mentioned before. The wine area is so very nice. And as far as beer or wine sold anywhere else other than at the Ariels Grotto restaurant (with the full bar service) that's it.
kaoden39, if you want beer with that Taste Pilots Grill Burger, you can take it over to the wharf area to eat, or bring your beer from the wharf to the Taste Pilot. You are allowed to buy a beer, or a glass of wine and saunter around DCA. I have never asked about the well drinks at the Cove, but why wouldn't you just sit there and relax with that drink?