Crepe Myrtles

Crepe myrtles top growth is really hardy in zone 6 to 7 or south. This far north they will freeze back to the ground pretty much every year. Some varieties do better than others. Also a warmer micro-climate helps with the winter kill.

I have seen crepe myrtles reach 5 feet in this area but that is following milder winters. Most stay below 4 feet because of the winter die-back.

Be patient they still might green up from the base - give them another couple of weeks.

Dennis - Johnson County Extension

I doubt you did anything wrong. This plant is really at the more northern parts where it can grow.

Most of them need to be treated like perennials in our area. In some warmer winter years and/or in a protected spot, some might come back from the tops. This is not usually the norm here.

Hopefully you should see more shoots coming up from the base as the ground warms. Things are rather slow this year as the cool has been hanging on and the soil in most places stays cool (wet makes the cold in the soil hang on longer).

If you scratch a branch's bark with your fingernail and see green just wait. If its brown, even if one of the 5ft ones, you will need to cut it back. If you follow the branch down scatching a small place till you see green that is a pretty good indication of where you could cut it back too.