I think it depends on the size of the new trunk and whether this has its own root system, the bigger the detached part, the bigger the root system needed to sustain it.
Now if you want to propagate take a piece of recent growth about a foot in length, dip it in rooting hormone (not absolutely necessary) stick it into a small container of sand(perhaps with your geranium cuttings) or any other well-draining medium and keeping it moist you should get a rooted specimen in the latter part of June.