Question
I've grown many healthy orchids but a couple weeks ago I noticed the roots of my dendrobiums are turning black (they look burn't) and the leaves are turning yellow and falling off. This is also happening to the new roots.  The ones that were spiking dried up.  This has been heartbreaking.

Answer
Tanya, it sounds like your dendrobium is entering its rest period. Many dendrobiums are deciduous and tend to lose their leaves during the rest period. This is when the plant goes dormant (or tries to).  Watering at this time can confuse the plant and may lead to rot.  You should back off from the watering until several weeks after you see new growth emerging from the base of the old growth.  Because most dendrobiums do not have a water storage organ (ie pseudobulb), you may need to lightly mist the plant during the rest period if  the canes begin to shrivel.  Do not attempt to feed the plant when it is at rest.