This rose garden story has tickled my fancy. Where I live roses are extremely long lived plants as long as the climate is favourable and they get plenty of sun and lots of mulch and blood & bone.
How big is the rose garden at Clarence House? I've been googling for information on the size of the garden but haven't found much. I have this wonderful image in my head of the garden from The Good Life - every inch of the garden space taken up with veggie plots and with a few chooks to snap up the snails and provide eggs, and maybe even a pig.
To provide enough organic veggies to feed guests on a regular basis, you'd need quite a large area. Unless he's also planning to plough up some of the parkland attached to one of the palaces, I don't think there's enough room.
I suspect an ulterior motive, I just can't imagine what it is.