Pruning very large Natchez Crepe Myrtles
We have three very large (about 30 ft) Natchez Crepe Myrtle trees ringing our patio. Apparently, until we moved into the house about 8 years ago, the previous owners had pruned them back every winter in the very way people tell you not to prune them -- to the nubby trunks. We stopped doing that and were blessed with the much larger trees that provide great shade, flowers and color in a graceful canopy. However, I'm a little worried about them. Each tree has many big limbs coming out of the trunk; I worry that there are too many. Some of the branches are now so long and so heavy that they bend in toward the house which means I need to clip them back. I'm not sure when they were planted but it was very likely when the house was built so that would mean they are 20 years old. How do I care for them (pruning etc) to ensure their health and nice shape? Do crepe myrtles have an expected life span?