Propagating crepe myrtle from rootling, outdoors covered with 1/2 inch of soil, should I place mulch on top to keep moist?

Question

Or does it need the warmth of the sun to sprout??

Answer 1

You might have better luck rooting them indoors with a plastic cover. Here's how:
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/how-to-propagate-crepe-myrtle-trees.htm