When my mom roots cuttings in water, she always insist that the water in the glass / jam jar / other container should not be exchanged, only topped up as needed. She even will place newer cuttings in the jars with older (by days or weeks) cuttings that have already started rooting. She claims that this process will actually promote root development. But she doesn’t have any kind of explanation (not that she’d bother with it1), just a “this is how it should be done”.
On the other hand, I am thinking about the growing biofilm (algae, bacteria...) and how this would probably affect the cuttings negatively. I would assume that starting with a clean container and occasionally switching the water when it starts to get murky - just like the recommendation for cut flowers - to prevent rotting is the way to go.
So could someone please help clarify:
Which is the better or correct approach? Should the water be exchanged regularly and the container cleaned or should it best be left alone until the cuttings are ready to be planted? Why?
I am looking for a reasonably scientific or at least logical explanation, please.
1 She’s been successful in rooting just about everything, even unintentionally, although she has a bit of a “survival of the fittest” attitude when it comes to caring for her plants - she’s not the most diligent person with watering, fertilizing or repotting.