I disagree that this is a good time. In your climate, you should wait until spring is securely in your area. Actually, I would think that this is an inappropriate time in any temperate climate! The existing foliage provides a freeze and frost buffer for your plant. And if you are experiencing a warm winter like so many of us are, pruning could actually force a flush of growth when you least want it.....NOW! Red Tips don't have several flushes of growth unless encouraged to do so, and then will readily oblige. This would not be a good thing in February (in your area). Pruning is, in fact, a growth PRODUCING act. If you cut your plant back, you may actually see an increase in growth, making it even more ungainly. Truthfully, one of the best and most successful methods of getting an over grown shrub back into control is by doing a proper 'renovation or rejuvenation' pruning. Though seemingly drastic, it almost always results in something FAR more desirable than hacking a shrub back to the size you think you want. You can then train and properly maintain that new growth into something attractive for many years to come. Red Tips are excellent candidates for rejuvenation pruning, by the way. You can expect to see 3 to 4 feet of beautiful new growth the very first year. The secret is in cutting the plants all the way back to the ground....6 inch stumps at the most. This should be done cleanly and evenly in the spring. Do NOT fertilize that year. Here is a link that might be useful: Just a bit of information about pruning

To be perfectly honest, they are not "overgrown" at all, although they may well be larger than you want :-) Photinias get to be large shrubs, even small trees - 20' is not out of reason. And despites Ken's suggestion, broadleaf evergreen shrubs are seldom included in what is typically called 'rejuvenation pruning' - that is usually limited to deciduous shrubs and really to caning deciduous shrubs. Broadleaf evergreen shrubs - like those typically used for hedging purposes: laurel, photinia, boxwood, holly, etc. - are often sheared, sometimes several times a season, to maintain a tidy and size-limiting appearance. And these types of shrubs can usually tolerate a pretty hard cut. Mid-summer is maybe not the ideal time, but you should be able to reduce by a third. Cutting back further may produce more stress than necessary at this time of year. You can cut back again in early spring as the plant pushes new growth. FWIW, several smaller pruning jobs during the course of the season are usually more beneficial than an infrequent major one.

What is white rock? Is it a rock? This stuff I have you can cut off, and ball it up and probably make a clay dinosaur out of it. I rarely dig (I am a no til gardener) that deep except to bury a bean pole, but next time I do I make make a clay?? type bowl and put it in the oven. I am no expert on soils or rocks. I do wish I did knew more on the subject. I do love my sunflowers that tend to volunteer from birdseed that the birds drag off better than the ones I plant! From what others say, I think my soil is pretty good. I did a perk test once to plant a tree, and was surprised it drained out of the hole. The hole was in a wettest part of the yard too. To missinformation, do know of a good website or book I can get that will tell me all about local conditions or the soil and the like? Are from this area too? Yes I could do a web search but unsure what to search for. And the thousand of hits out there it takes weeks to do research on a topic. I had tons gardening bookmarks , but lost them all a few weeks ago due to a computer glitch. It is depressing. I had lots of source of seeds I intended to buy one day, links to soil health sites, no till gardening, history of veggies, link to weeds I have in my yard/garden. Links to photos of trees and wildflowers I would like to get. links to neat looking trellis designs, neat sites of other's texas gardens. I had so much fun stuff. Not sure all what , but gone now.

Since you have such warm winters with only occasional shots of northers blowing in, with cold that lasts only a few days prior to your temps warming up again, why not try the air layering propagating methods on your RTP. To find out how that is done check the Purdue agricultural extension website. Of course that idea does not help with the cuttings you currently have.