What type of dendrobium is it? If it is a phal-type, it will bloom a few times a year so it will probably try again next month if the culture is good. They even bloom on the leafless canes. Mine usually begin new spikes as the old ones die. Blossoms will last about 2 1/2 to 3 months. I keep mine in large lava rock and plastic net pots and water once a week during the winter. Two of my four resent repotting and lose leaves while the other two don't care. They like really bright light (I have mine near a south-facing window) and prefer the medium to dry completely (and then some) between waterings, especially in the winter.
Of course, if you have the other type of dendrobium, I am completely clueless. I have a little one that just does its own thing, ignoring the rules set down for it.