I usually lay the stem on the ground and cover it with soil and mulch while it is attached to the mother plant. That gives me good results. But I have pruned back severely and, not wanting to waste the cuttings, I have laid the cuttings in a shallow tray with soil and mulch. Roots appear at every node along the stem; I later cut them apart and have plenty to share.
[Note of thanks to Jane Straus, author of "The Blue Book of Grammar and Punctuation" because I never get that whole 'lay/lie/laid/lied' thing straight by myself.
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