Looks like he should be full time by May - LaRussa is just being LaRussa and figuring out what he has to work with during April, from Rotoworld:
Despite only starting six of the Cardinals' first nine games, Ryan Ludwick is confident he'll soon be an everday player.
Manager Tony La Russa plans to continue cycling through his four outfielders during the first month of the season, but hopes to settle on a more permanent lineup by May. "[Tony] said, 'Trust me.' And I do," Ludwick said. "Look at what happened last year. I trusted him, and I played."