"I think the hedge could be lost, and some of the replanted shrubs and plants - I don't know if they'll come away again."
Hospital security manager Robert Thorpe said there was a "zero tolerance" attitude towards vandalism on the grounds, and if the perpetrators were caught in the act they would be handed over to police.
"Kids hanging around the hospital are a problem and we escorted a group out the main front doors on Tuesday night.
"Some cars were later damaged, as well as the garden. Perhaps it was revenge. We know police later arrested a group on other matters."
One of the driving forces behind the garden, co-ordinating hospital chaplain Barbara Walker, said it was hugely disappointing that an area designed as a place of reflection for patients and their families could be targeted.
"Mindless vandalism or theft is disappointing, but this is an important space for the use of people under great stress," Reverend Walker said. "Not only that, the garden is funded through donations, out of the goodness of people's hearts."