When propagating herb cuttings, it is a good idea to use some sort of rooting compound. I prefer using willow twigs and making my own.
Willow twigs are cut in their growing period, which means early spring. Cut them into short 1 inch lengths and place upright, in a glass. Add 1/2 a cup of boiling hot water and cover until cool. This resulting solution is your rooting compound. Use it right away for best results.
I have had great luck for years, using these exact directions. I found out about this technique that was perfected by Dr. Makota Kawase, who studied the effectiveness of willow water in the 1960's.
Willow water is a safe and effective alternative to powdered rooting hormone.