Dendrobium Nobile

[weitoi]

I have a question regarding Dendrobium Nobile. I had a couple of plants that are doing really well, and one has two buds that will soon open and bloom. What I have noticed is, the roots on the older part of the plant seem black to dark brown and they appear dead. The newer stems have nice new healthy roots. Is it normal for the roots on the older part of the plant to die off, while the newer pseudo's produce nice new healthy roots?
I'm new with the Nobile Den's, and I noticed it on two plants. Neither of them is unhealthy... they look very good.
Thank you.

[chidlove]

It could be . The old psuedos are still beneficial to the plant,but the roots might not look very good