Just to let you know, It also crashes on my iPhone 5, I can only see the black and white UNREAL ENGINE U4 logo and then it crashes.
Hey Playamango,
Thanks again for reporting this issue. There have been multiple users reporting this issue. You can find the Forum post here: Can't run Zen Garden Demo - Feedback for Unreal Engine team - Unreal Engine Forums. You can also find numerous other AnswerHub posts able Zen Garden as well.
Though the iPhone5 is not listed on that list, it is one of the devices that will not be able to run Zen garden. You will be able to download Zen Garden but the Processor of the iPhone 5 does not support metal and will be unable to open the application.
Thanks and have a great day!