I have 5 crepe myrtles approximately 6-7 yrs old. All were pruned but the existing shoots are not growing. I have new growth coming up from the bottom but the existing are dry and brittle. I live in NW Arkansas and we had a very hard winter last year with lots of snow and low (under 10 degrees). Should I cut off all the old plant to let the new prosper? Thank you.
These shoots at the bottom are referred to as suckers. A plant sucker is an effort by the tree to grow more branches, especially if the tree is under stress, which in this case probably is. However, in time the tree should come back out just fine, though blooming will be inhibited for a while. The following articles should be of some help to you: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm