In the test tube at university lab there was a too-little/too-much/just-right concentration for these things. I have no feel for how it might be at the less temperamental hobbyist level. The hobbyist has variations in pH, temperature, moisture and lighting that were all controlled in the laboratory.

Should you have the time and inclination to test several products and methods side by side I guessing you probably will not see very much difference unless you do scores of tests.

So you don't think that soaking cuttings in a hormone solution would be any better than putting them in a powder that washes right off?

The sand I use is already moist but I water them in to make sure the cuttings have the best contact with no air pockets. Even if I didn't water immediately they'd be watered in a day or two so I still think a lot of it would wash off. Maybe the cuttings take up the hormone pretty quickly so possibly it doesn't matter if it washes off, I don't know.

I do often make holes to put the cuttings in, sometimes not. I ordered some Dip 'n Grow earlier today so will see how that does. If there are directions on there for diluting it I'll follow the directions. My main question is whether a hormone would be absorbed better if the cutting soaked in it awhile. Guess I'd have to find the best amount of time to soak them. The old willow water method comes to mind. I root hundreds of rose cuttings every year so what I'm doing works about 90%. There are some difficult to root varieties so I'm looking for solutions.

Here is a link to an article about willows. If you scroll down you will see " How it works" and how to make willow water. I think I tried it a long time ago but want to try it again. It sounds like it could help prevent bacterial and fungal problems on cuttings also. In this article the author suggested that watering a couple of times with this solution could help with cuttings that have already been stuck. That has been in the back of my mind awhile...that you could just water in some additional hormone boost. Perhaps a little aspirin in water might help cuttings, if salicylic acid boosts immunity.

https://deepgreenpermaculture.com/diy-instructions/home-made-plant-rooting-hormone-willow-water/

I've never seen any difference with the store bought stuff with cuttings. I've done tests with and without store bought stuff and had the same results both ways. Either they all rooted or they all didn't.

I've had fast roots when using a concentration I mix myself from pure indole-3-butyric acid bought off ebay while doing air layering, but I've never done a test where some were treated and some weren't, so I can't say for sure if it helped or not. Maybe that's something to try this fall.

I've been meaning to try that toothpick technique with air layering too.

I used the Dip 'n Grow yesterday. They recommend a weak solution for softwood cuttings such as I usually take. They advise only putting the cutting in the solution for 3 to 5 seconds. I guess the cutting must take up the hormone in that amount of time. I might call their help line and ask them about that. Since I'm thinking that soaking a cutting awhile might help, maybe an extremely diluted Dip 'n Grow solution would work for that. When people make willow water I'm sure the concentration of hormone varies a lot but I bet it's weak.

The directions on Dip 'n Grow also say to throw out any unused solution after ten hours. Has anyone tested that to see if it loses effectiveness that quickly? I'm thinking maybe a little of it could be added to a gallon of water and used to water recalcitrant cuttings. I still have some old rose cuttings I took in winter or Feb. which are just sitting there. Mostly it's the old roses like gallicas, centifolias, or mosses that are hard to root. Most modern roses root easily. Some of the old ones root easily.

Yesterday I scrubbed pots and chlorined them before putting sand in them and sticking cuttings. Some of my cuttings rot before they can root. That's one reason I don't do anything to add humidity...they rot more if in a plastic bag, for example. But there might be something I can do differently to combat rot. Maybe use a different medium than sand. I tried potting soil, no better. Maybe coir. There is a little rooting block thing..I forget the name of it, that might be worth a try.