Back in October, Gargantia on the Verduous Planet's official Twitter announct, along with Digitaro of Nitro+, announced that a sequel to the anime had been green-lit. Further details are now scheduled to be revealed at 1pm on March 23 at the AnimeJapan 2014 Open Stage.
AnimeJapan is a new event for 2014, formed with the merging of the Tokyo International Anime Fair with the Anime Contents Expo and organized by the AnimeJapan Executive Committee with support from The Association of Japanese Animations and The Association of Manga Publishers.
The photo Digitaro posted shows the announcement of sequel on the screen, above. The announcement of the sequel has not been further clarified yet and can be anything from a second season of the anime, OVA or feature film.