"W" wrote:

What is the minimum spacing you can use between plants in a hedge made of
Photinia Red Robin? I want to be aggressive about this and I want to
maximize the density of the hedge. I am willing to have the health of
individual plants be sub optimal if that means the hedge overall will be
denser.

It's patently obvious you shouldn't be gardening, you've no patience
for plants to grow. Greater spacing between plants is *always* better
for plant health than closer spacing... that's true for all plants...
allow space for plants to attain their natural growth habit. Best to
err on the side of more generous spacing.
http://homeguides.sfgate.com/use-pho...dge-23785.html