Question
Hello!
I have rescued a new phalenopsis orchid and it badly needed to be repotted. It had lots of very long yellow and dry roots and not many roots that looked healthy. I went ahead and cut most of the roots off down to the bottom of plant leaving a few.
Was that the right thing to do or should I have left some of the longer roots?


Answer
Amanda, good for you for recognizing the need to repot.  You should definitely not remove roots that are firm and turn green when wet (ie sometimes they can be a yellow if the potting mix was too degraded to allow light to get to the roots).  Those are the healthy roots that will generate new growth.  On the other side of the coin, those roots that are mushy or stringy should be removed as they are dead and no longer serve a useful function. There may be roots that don't clearly fall at either extreme.  My preference is to leave those as they may not have received enough moisture and formed a protective coating to prevent moisture loss.  Orchid roots primarily consist of two parts. The root hair, in the center of the root, conducts nutrients to the plant from the outer coating called the velamin.  The velamin absorbs nutrients and moisture from the potting mix.  It is spongy and also contains chloroplasts which can use light to manufacture some of the plant's nutrients.  The chloroplasts, which contain chlorophyll, like leaves, is responsible for the green color observed when a healthy root is wet. When in doubt as to whether to cut or not to cut, do not cut the root as the potential benefits of a good root outweigh the damage done by retaining a poor root.