It’s all down to salicylic acid which is a plant hormone. Its a component of hormone rooting powder but it’s also readily available from willow bark where its anti-inflammatory properties also go to make aspirin.
I’ve been experimenting with it in my permaculture garden. Recently I went on a apple grafting workshop. I left with a graft of a Blenheim Orange scion on top of an M26 root stock – which is all well and good but I want to be able to grow my own root stock in the future so I also left with three M26 root stocks. You would normally use these as the lower part of each graft but if you want more of them you need to establish them for a season, coppice them close to the ground and then mound up the resulting crown. A whole two years later you may have five or six root stocks from your original one.
Anyway, impatient as I am I cut one of them a year early to see if it would take and, not wanting to waste the cut bit from the root stock I put it in a jar of water with lots of strips of willow bark. It went into the ground next to the other three a week later. Three weeks on from that you can see the results for yourself:
The cutting, which would normally be discarded, as unlike a willow cutting, it wouldn’t normally be expected to take on its own, is sprouting leaves way ahead of the others.
Here are the others.
I’ve now filled some empty plastic bottles with water and willow bark shavings. I’m putting it on all of my cuttings and seedlings.