For what it is worth I was alway told that all that rooting powder does is cause an irritation to the tender end of a cutting, and if you use too much you can do the reverse of what you are trying to achieve because the powder becomes saturated and the cutting cant breath.
Apparently the plant reacts to the powder creating callousing which is followed by roots.
Not very scientific I know but when I grew Chrysants & Dahlias for a hobby I found very little difference between using a powder/liquid to the grit method*
, in fact I usually used both methods.*
This is where you cover the rooting compost with a layer of silver sand which percolates into the hole as you push in the cutting.
The sand causes the irritation, you are ensured that the cutting is in total contact with the compost/sand and the cutting is surrounded by a free draining medium thus reducing the chances of damping off/rot
Because most hormone powders have a short shelf life (it is said it should be replaced every year) I sometimes did not bother if I was unsure of how long I had had my powder.
This is my slant on taking cuttings:
For specific types of cutting click on the 'related link' in the right hand column.
I hope you find this info useful...Tg