Here in the Pacific Northwest, photinias are trees. 20 feet is nothing. The rhododendrons here also grow to be 20 feet tall. So do the Himalayan blackberry vines, one of the 10 plagues of the Pacific Northwest. When I moved out here, I employed the strategy I had learned elsewhere of planting 20 things for every one that will survive. Here, I plant 20 things and, not only do they all survive, they produce 40 more within a year. Garden plants seem to spontaneously generate. LOL!