why does my lavatera x rosea shrub not producing flowers?

Well if it was only planted in the spring it has had a hard time of it with the dry weather most of us have been enjoying...!!
Your weather around there has been the same I think.. I would water it & give it a couple of feeds before the Autumn now to help it get through the next winter & then hopefully next spring it will burst into life & give you a great show next year.. I think if planted in Spring you do only get a short flowering period the first year, plus they de require a descent amount of water... This summer being so dry will be causing it problems.... So water it & a couple of feeds & hopefully that will get it ready for next year now... :thumb: