Back in March, Gargantia's production pipeline seemed to be in exceptionally good shape. Blu-rays of the first two episodes were being distributed at the Anime Content Expo before the series' TV premiere. Writer Gen Urobuchi was saying that he had seen the completed storyboards for the final episode. It now seems like the machine wasn't quite so well oiled, as the first Blu-ray set has been delayed a month from the previously planned July 26th release date.
Production delays on the OVA are the credited reason. The release dates for the second (September 25) and third (October 25) Blu-ray boxes are currently unaffected.
The series producers have also stated that from episode 5 onwards, the Blu-ray versions will have considerable improvements on the TV broadcast versions.