Crapemyrtle and Weigela are both very easy to propagate from cuttings. Let's try to figure out why you've been unsuccessful. It sounds like your rooting mixture might be too heavy, dense, mucky, etc.

The rooting medium must be well draining and coarse in texture. Using the soil from your garden in containers in never a good idea. I use a very good soilless potting medium with lots of extra perlite when I root cuttings. Some people simply use perlite. Others use just sand, but I don't think enough oxygen gets to the roots with sand.

Take 5 or 6 inch soft wood cuttings (May-June, remove all but the top three or four leaves and insert in the wet medium. Water in again to insure stem to medium contact. Cover with a plastic bag, plastic wrap, plastic bottle, etc. DO provide small air holes. Place the rooting flat (or pot) in a shady location. If your soil is very porous, make sure that you keep it moist, but do not disturb the cuttings when watering.

You can also take hardwood cuttings of the weigela, which root just as quickly. In three or four weeks, you should have roots forming.

Here is a link that might be useful: Propagation tips

Hmmm....
I'm thinking my soil might be the problem. I'm following all your other directions already, so I'm on the right track.
I'll stop today and pick up something with perlite in it. I'd really love to save this little snipped ot 'Crimson Sentry' maple. It was SO gorgeous in the sunlight. I also set up some cuttings of weigelia 'Lucifer' yesterday. What a gorgeous red!

Anyway, I made certain to have a pinch of the main tree/branch with them. I'm hoping this along with my new and improved soil, will offer me better luck. I will get back to you just to let you know how it goes.

Thanks for taking the time to share.

Christine, remember....think in terms of AIR spaces when it comes to rooting cuttings (or growing anything in a container). The coarser the rooting medium, the better. If you are already using a commerical soilless potting medium, perhaps you can just cut it with a large volume of perlite. Most of the products that I have seen don't have anywhere near the amount of chunky stuff in them.

Good luck!