Once established, I don't think you can over-abuse crepe myrtles. Also, I don't think it matters when you prune them. If you are going to remove some of the larger trunks, decide which ones to remove. Mark them with a dot of spray paint to identify them later. Be sure to consider what needs to be removed and what not to remove. Try to keep the plants pleasing to the eye but remember they will quickly recover next spring. Take a chain saw or a bow saw and start cutting. You will have new shoots come out this summer and autumn which may get fried by cold weather this winter because they will be young and tender. Don't worry, they'll come back next spring.

I believe the expected lifespan for Crape Myrtles is very long. There are many really old old ones around older homes, especially in the Deep South. There are few trees around that can compete, in my opinion, with mature Natchez Crape Myrtles - great flower clusters and the bark is incredible.

Actually, though these trees have a reputation for being tough, they should be cared for in a way that improves their chances for a long life.

I'm sorry that your trees have had a history of being topped. Though you can shape them to improve them, they will never quite have the beautiful 'bones' of a tree that hasn't been butchered.

The best time to prune these trees is in the dormant season when you can see what you are doing! It will be much easier to pick and choose which limbs need to be removed for aesthetics and safety. I see no reason to spray paint the limbs first.

Pruning is an art form and an acquired skill. If done improperly, you CAN ruin your tree. If done correctly, you will be able to improve the health and appearance of your trees a great deal. There is quite a bit of good information on the internet about making proper cuts, tools, etc. Plus, there are some good illustrated books out there.

I strongly believe that if a tree is too large to be pruned without a ladder, then a homeowner has no business with a chain saw in his hand. Most crape myrtle pruning can be done with a tree saw (large and small), and some good loppers. A good tree saw, by the way, cuts through branches like a knife through butter.

Do you happen to live anywhere near Huntsville? I'm going to conduct a (free) crape myrtle pruning class sometime this winter.

Do you need to seal the large cuts?

Never put any sealer or paint over large (or small) pruning cuts.

Mike Pender of Classic Gardens has some excellent information on his website about pruning crapes, and how to recover one from bad pruning.

Also, remember there are smaller and dwarf varieties of crapes if you need to put one in an area where a large one wouldn't work.

Here is a link that might be useful: Crape Murder