I use either potting mix or sand. Worm castings are great to mix with your potting mixes and container plants, but should not be used alone for either starting seed, or rooting cuttings - they hold too much water and you can have rotting issues. I worked with a casting producer for a couple of seasons trying to come up with a casting-based potting mix. We found the best thing to do was just mix some castings into an already formulated potting mix. 20% castings is about the max you want your mix to contain. Check the cuttings when you start to notice a little new growth. I usually leave everything alone for about 3 weeks, then my curiosity gets the best of me, and I have to check them. Since you are using glass, you will probably be able to see roots form. Then you can put them in their new homes!