So far this is all I've found:

You can root hoyas from as little as a one-node cutting to produce another plant, but it's best to start cuttings with at least 3 leaf nodes (remove the leaves from the lowest node and put that node into the propagation mix).

here is the only other information I was able to find:

I started out with 4 leaves dipped in root medium I forgotton in the trunk of the car for a number of days when I realized what I had done I panicked however they had begun to root in the ziplock bag I planted in a 4 " pot has has been there in a east window ever since, I fertilize it once in spring and again summer once and let dry out between waterings and mist twice a week

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