very interesting question Joseph.
I find my self pondering what could happen....
The new plants already have
roots growing and i am not sure speeding this up would be beneficial for the plants. It seems having nice garden soil would be what would be most beneficial for new seedlings.
Given that the new plants already have roots, i see this as maybe being useful. I wouldn't say do not water your little plants with willow water, it most likely would help them, though i am not sure on exactly how helpful it would be.
Maybe this would be helpful to use when you are transplanting a plant into the garden after being inside in a little pot? i am really not sure.
Do you have an excess of willow water?!? or is this mainly theoretical? Do you have little plants struggling?
Flipping this on its head, lets say you could increase the growth rate of the leafs with some magic bean water. The leaves grow faster than the roots can and the plant falls over due to being to top heavy. So maybe adding this to the plant would create additional stress on the plant to create more leaves in order to
feed the quickly growing
root mass. With out their being
enough leaves the roots starve and than slow down until the top catches up?
I am merely speculating. Fun little exercise!
anyways for what its worth!