All Red Tip Photinias need to be pruned, from the very young to the totally overgrown neglected older plant. You will learn how to and when is the best time to prune and train them to make them beautiful and bushy.
The best time of year to prune your Photinia is early spring through early fall. Late spring, early summer being the best. If you have just planted then you would want to wait until you get some growth to start pruning. Red Tip Photinia hedges are fast growing and if you want to have a nice, full, beautiful Photinia then it must be pruned. The how of pruning really depends on the why you're pruning.
To train the Photinia start pruning early and trim off at the bottom to fairly short. Doing this often will give you a nice dense base near the ground. Then trim the sides to make it narrower towards the top so the sun can get to the lower branches, giving them a healthy start and producing many leaves.
If your Phontina is older and has grown tall and skinny, or you have more than one together and they are uneven, you can even them out by cutting the top branches very short and keep them short until you see the bottom branches getting fuller. Cut the lower branches fairly short again until you start to get the bushiness you desire. Then you just have to keep up with maintenance to keep them even. If you have more than one they will eventually blend together.
Now, let's assume you just moved into a new house and in the yard is a completely out of control Photinia. In the early spring, you can cut the entire hedge back to 6 or 7 inches from the ground. It will start to grow back to the tune of 3 to 4 feet that same year and you can start to train it the way you want it.
Have patience, getting your hedge to look the way you want it takes time, even for the faster growers.
Make sure you wait until all threats of frost are over for the spring. Pruning before a frost can leave the plant susceptible to diseases and insect problems.