A: Many people make the mistake of assuming that since orchids are native to tropical rainforests, they must be watered several times a week. Unfortunately, watering this frequently will kill the roots of any orchid in short order. The general rule of thumb for orchids grown in the home is to water every 5 to 12 days, depending on the type of orchid, the temperature the plant is grown in, and the time of year. During the warm summer months when days are long, more frequent watering is required than in the cooler, shorter days of winter.
There are three basic types of orchids, as far as watering is concerned: those that should be kept evenly moist at all times; those that should be allowed to nearly dry out between waterings, except when in active growth; and those that should always be allowed to dry out a bit between waterings. The guidelines below list the major varieties of orchid in each type.
Varieties to keep evenly moist (not soggy or wet) at all times:
Paphiopedilum, Miltonia, Cymbidium, Odontoglossum,
Varieties to keep evenly moist during active growth, allowed to dry out between waterings when not:
Cattleya, Oncidium, Brassia, Dendrobium.
Varieties to keep nearly dry between waterings:
Phalaenopsis, Vanda, Ascocenda.
In a family of plants as large as Orchidaceae, there are, of course, exceptions to these rules. Always be sure to call and ask for watering instructions when you receive a variety of orchid with which you are unfamiliar.