Dendrobium Leaves Turning Yellow & Falling Off

[quiltergal]

Dendrobiums are rhizominous, meaning the canes are connected together by a rhizome. In the case of Dens like yours the rhizome is very short and pretty much invisible. The colony of canes are actually one plant. Sometimes when a plant suffers severe root rot, the rot extends to the rhizome as well and that is why your one small piece fell off the main plant. So, technically you now have 2 plants.

Most rhizominous plants have two growth "eyes". It's kind of emergency backup in case a new growth is damaged or diseased. The plant will "activate" the second growth eye in order to save itself. Any cane that has matured..(not growing any new leaves or has bloomed) is considered old growth and will not grow any new roots. New root growth always comes from new canes still growing.

Dendrobium roots are very slender and fine. The actively growing tips are bright green and shiny, and as the root elongates you will see white velamin (a sponge like root tissue which surrounds to root, that absorbs water and sends it to the root core). So look for small, shiny bright green nubbins to pop out near the base of that new cane.