Germinating these is easy. When you get your seeds, you can use the seed packet they came in to stratify them. You must stratify them for 60 days!! No exceptions to this rule.
So, my seeds come in a real nice ziplock baggy (the bags were a gift from @RickCorey
, thank you!). I then add quite a bit of dry vermiculite. If you don't have that you can use fine sterile potting soil. Mix it up really nice so the seeds are evenly distributed throughout the bag. Then add just enough water to the bag to moisten the contents. I use reverse osmosis water. I wouldn't want to add chlorinated water (but I'm not sure if that's just my paranoia.)
Mark with a sharpee the variety name and today's date on the outside of the bag, and put it in the fridge.
What I do is every couple weeks, take it, open it up, dump the contents into a clean bowl, mix it up quite a bit, and let it breath for a few minutes. Then repack it into the baggy and put it back into the fridge. Once the 60 days are up, take the contents out and spread them onto a folded paper towel. Spread it as evenly as possible, then fold in half and put it into a large ziplock or sandwich bag and place under growlights. (This is a form of the "paper towel method", which I'm sure you're all familiar with.)
Keep it warm (a heating pad helps). Check it daily. Within a few days you'll start to see germination. Pick each seedling out as they germinate and pot them into cells.
Transplant into the garden as soon as you think they are ready (the earlier the better! They languish when stuck in little pots). Make sure frost is long past. KEEP THEM WARM. Crepe Myrtles absolutely hate the cold and will be stunted, sometimes permanently. If it's cold outside, keep them inside your house.
I think I waited until mid to late April to transplant them into the ground.
This is what my bed looked like in mid July of the same year:
You see they are all about 12 inches tall. About half of them bloomed in mid August and beyond.