Credit: Hub Pages

I find that plants which are harder to propagate through cuttings have a higher rooting chance through air layering. And, to increase the chances of the stalk rooting, I like to use a knife to make a cut through the stalk, usually about quarter- or halfway. Then, I smear rooting powder on that open wound, and bury that portion in the soil, and pin it down.

Apparently, open wounds on the plants (and open wounds nearer to plant nodes) encourage rooting. The rooting powder should encourage it a lot further.

I am trying this on my lemon verbena right now. I shall report any progress I have.