The short answer is never! You should not get black sheaths in good growing conditions.

Thanks, I'll go ahead and remove the sheath and research what causes dry sheaths (or no sheaths) to determine what needs tweaking in my growing conditions.

Donna, you must be doing most things right to get blooms.
Problems with black sheaths might arise if you had a "Cattleya" that develops a sheath and then waits six months before the buds develop.
I've put a link to a previous discussion re. sheaths etc.

Here is a link that might be useful: previous discussion

Basically if that does happen which arthrum says it shouldn't, just flick at the top point of the sheath gently. If it won't budge wait a few days and try again. That is if it's partially open.

This post was edited by CooperDR on Mon, Nov 24, 14 at 20:37

Thanks again for the info. I removed the black sheath, then left home for the holiday. Free of the sheath, the bud really got to the business of opening while I was away:

{{gwi:204435}}

{{gwi:204436}}
This flower is still opening and it smells wonderful.