The really heavy feeders, like Catasetinae in rapid growth period, and Cymbidiums, get a top dressing of time-release fertilizer to supplement whatever they get from my infrequent fertilizing. I don't grow a lot of Vandas (stick mostly to the relatively few cool-growing species... no room in the GH for big things) but they get whatever they get, and bloom anyway. (Things like V. tricolor, V. roeblingiana, V, coerulea, and even Ren. imschootinana)