Hormone rooting powder - does it work?

For some reason, last year I didn’t get round to taking cuttings of my favourite pelargoniums when I should have taken them in the summer, and it was well into autumn before I even thought about it. These are pelargoniums that were originally given to me by Carol (Edwards); they have a coral coloured flower, are very reliable and an all-round good doer. Generally their cuttings take well but it was getting late on and I was worried I might lose them this time. Finding a pot of hormone rooting powder (HRP) lurking in the greenhouse, I thought that might help. Then I thought about my late father’s advice, which was to leave the cuttings to dry out and callus over before putting then in the compost. It soon occurred to me that, having plenty of potential cutting material, I had the basis of a little experiment…

And these are the results:

Pot 1 - cuttings dried then dipped in HRP - success rate 3 out of 5
Pot 2 - cuttings dried but left plain - success rate 4 out of 6
Pot 3 - cuttings left plain and planted immediately - success rate 3 out of 5
Pot 4 - cuttings dipped in HRP and planted immediately - success rate 0 out of 5

So from this it would seem that drying out and letting the cutting callus over gives the greatest benefit. The HRP didn’t seem do much good at all and the cuttings in Pot 4 would probably have been better without it.

Of course it wasn’t a fair experiment. The pots weren’t sterilised. I’m not sure that compost was the same in each pot. Did I water each pot equally? And the HRP had definitely been hanging around in the shed for ages.

I wonder if anyone has had a better success rate with HRP, swears by it and can tell me what I was doing wrong? But until then I shall stick with my Dad’s advice and just let them dry out - he always knew best.