In article , Peter Sutton
says...

Its a huge subject, and I was really only questioning the speed at which
roots form. I had always assumed that they grew at a linear rate, ie after
10 days the roots were twice as long as after 5 days. But my recent
observation implies that for 10 days nothing appears to happen, then two
inch roots can suddenly grow in only two or three days.




It can vary enormously. The Mrs plants cuttings of Red Robin (Photinia)
not sure of spelling. We've lifted ones that look fine a year after
planting as cuttings and they have had no roots at all! However, when
they suddenly start to spurt it is a sure sign they have finally put
roots out.
--
David in Normandy