You can use slow-release fertilizer on orchids. Several commercial
nurseries do it, and I know hobbyists who do it. I've always been told not
to use Osmocote because it is too temperature dependent. Dynamite/Nutricote
(I think they're the same thing) are supposed to be much better. There's
another one advertised for orchids (Throw-and-Grow or something like that).
-danny