The proper frequency of watering will depend on the climatic conditions of the region you live in and inside your home. Orchids require more frequent watering during the warmer months, when they are actively growing, than during the cooler, shorter days of winter.
Humidity is the amount of water in the air, and orchids need a lot of it. During drier months or in homes that are heated, humidity may be supplemented by misting and use of evaporation trays.
The type of potting medium being used also has an impact on your plant's water requirements. Potting mediums that are designed to work for a large range of orchids typically have a mix of bark, sphagnum moss, Styrofoam and various other components that hold moisture while encouraging good drainage. Mixes composed primarily of less absorbent materials such as bark and cork will not hold water as well as those that contain highly absorbent substances like sphagnum moss.
New, previously unused, growing mediums have a “breaking in” period when they are not a porous as the older growing mediums surrounding plants that haven’t been repotted recently. An orchid recently repotted will need to be exposed to water for a longer amount of time in order for the fresh growing medium to soak up and hold moisture.
The size of your orchid container also influences how often you need to water, regardless of climate conditions. Smaller pots need to be watered more frequently than do larger pots.
The type of pot can also affect how quickly the plant will dry out. Orchids in plastic pots will stay moist much longer than those in porous, clay pots. Good drainage and air circulation are vital to an orchid’s health, and there are a wide variety of specialty pots and baskets available that are uniquely designed for use with orchids.
The quality and temperature of water used, whether for spraying or watering, is extremely important. Tap water is typically treated with chlorine, and well water with salts to soften remove hard water ions. Therefore, tap water should be used with caution.
The best water for orchids is undoubtedly rainwater. Rainwater, as it passes through the air, dissolves and absorbs many substances such as dust, pollen and other organic matter. This enriched rainwater contributes to the nourishment of the plant and contains fewer harmful chemicals than does tap water.
The temperature of the water is also important. The water that you use for your orchid should be room temperature. Cold waterings can, over time, shock and damage your orchid. To make waterings as easy as possible, purchase a large container of distilled water just for your orchids, and don’t refrigerate it.
Any plant is more likely to thrive when the conditions of its natural environment are duplicated as closely as possible. This is certainly true of orchids, which have specific needs for humidity, temperature, air movement, growing medium and water. Knowing how to water an orchid includes understand some of the environmental factors that affect your orchid's water needs. But don’t get overwhelmed, see the Suite101 Orchid Article Series for all the basics.
If you are an orchid novice, start things off right by purchasing a healthy plant and a variety of orchid that is easy to grow. Supplement your knowledge with one of the many excellent books and web sites devoted to orchids, including the American Orchid Society (AOS).
To learn more about container gardening in general, see the Suite101 article Container or Backyard Gardening.