Depends on the location of your plant. Outdoor Vandas transpire more quickly than indoor ones, and may need to be watered and misted several times a day. The higher the humidity, the more sun they can take, which leads to flowering. Rebecca Northen recommends high nitrogen feed if the plant is in bark, balanced if the plant is in osmunda or tree fern. Do not use fertilizers containing urea on orchids, because urea requires breakdown by soil microbes that aren't generally in orchid media.
Toxic salts can build up and damage roots.
Alternate your brands of inorganic fertilizers regularly to offer your plants the widest possible array of trace nutrients. For organic fertilizers, place about 3 handfuls of poultry manure in a 3-5 gallon bucket. Fill with water and allow to stand 2-4 weeks, occasionally giving it a stir. It is ready to use when it loses its cloudy appearance. Strain through muslin or other cloth and add water until it is a very light brown.