Till they do, or till they crumble when light pressure is applied, far as I
can tell. I've got one of mine showing two keikies, the other cane hasn't
done anything so far.
Be patient,
Murri

"Larry" wrote in message
...
How long should I give the canes a chance to develop new roots?

L.

"V_coerulea" wrote in message
...
Dendrobium backbulbs will frequently throw new shoots which will root.
You can stake it in a small clay pot (for the weight) with a well drained
mix and only mist until new growth shows. Alternately you can lie the
canes down on a bed of spaghnum. Many joints should throw keikis (new
young plants) which can then be detached and grown on their own. If the
canes are yellow or soft just toss them as they won't grow anything.
Gary