I don't know nor could I find it in a couple of minutes of google searching - and my google-fu is strong! ;) So here's what I think - others please chime in and tell me I'm full of hooey if you know how to do it and I'm out in left-field someplace.

I think that yarrow varieties that produce long, very sturdy stalks would be key to making I Ching pieces. I would think looking for an Asian source of yarrow seed (to grow your own) or search the wilds and gardens for a plant that has the qualities you are searching for is important. Cultivate/propagate those plants with the desired qualities.

Grow those plants in a windy, open place in a single row so they all get the most wind abuse possible. This will cause the plant to have more sturdy as opposed to thin and weak stalks. Thin, weak stalks won't stand up to the wind so the plant will compensate - this is part of why house grown plants are so weak and need to be "hardened off" before planting outdoors. They have been separated from Mother Nature and so they could not benefit from the wind, rain, and weather making them strong.

Keep weeds clipped around the yarrow. If a plant throws multiple flower spikes, you may choose to selectively prune those you don't want so the plant devotes more energy on the one you want.

Finally, harvest toward the end of the season. Remove any leaves or flowers. Cut to length while there is still some greeness to it. Do any other smoothing or stick processing now. I think fiddling around too much with this work after they are dry is asking for trouble. Let them air dry in a single layer on a screen. Once completely dry, put on some sort of sealer or finish to help give them strength and to give them a nice feel when using for divination.

I'm not sure if this helps you but it is what I would do if I wanted to create I Ching pieces. Good luck with it!!

FataMorgana