I have 3 crepe myrtles on my property, around 15' - 20' tall. When I moved in 22 years ago, they were already close to this size. The past few years they are looking thin, and flowering less and less. Are they coming to the end of their lifespan, or do I just need to prune and fertilize - I haven't done much of either. I live in Fla, Tampa Bay area.
Old Crepe Myrtles
Certified GKH Gardening Expert
It is hard to say for certain. With good care, the trees have a fairly long lifespan. If they have not been pruned, this could be an issue. These articles should be of some help: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm