As I mentioned above, overwatering is a common cause for dead orchids. People typically ask about a plant's water needs by inquiring how often they should water, and it's this "how often" mindset that is a big part of the problem. How often you should water a plant depends on how much water it uses, which is a function of humidity, light, air movement, and what its roots are growing in. Watering by the calendar rather than a plant's needs is a recipe for failure.
So the short answer to the question of when to water most orchids, including Phalaenopsis and Cattleya, is: Just before it goes dry. How often is that? In practice, it can vary from every few days to every couple of weeks. It depends on the orchid and on the conditions in your home. One of those conditions -- an important one -- is the medium the orchid is growing in.
The best way to judge moisture is the old-fashioned way -- stick your finger in the planting medium. Pull it out, then rub your fingers together. You can easily feel if any moisture is present. If you don't feel any, it's time to water. Eventually, you'll develop a sense of how often to water, and how conditions (seasonal changes, for example) affect frequency. You'll also develop a "feel" for how heavy the pot is when the planting medium is dry, another way to gauge moisture levels.
McHatton offers a useful suggestion: A few suppliers (Charley's Greenhouse, for example) sell clear plastic pots. When moss or bark -- the best planting media for orchids -- is moist, you'll see the condensation on the inside of the pot. When it's dry, you won't, and you'll know it's time to water again.
Watering is no more complicated than pouring water into the potting medium and letting the excess drain through the bottom. I've noticed that some orchids available in stores are in pots with no drainage holes. That makes it far more difficult to water properly, so I'd suggest repotting in a different container (or drilling holes, if you have the tools).
Continued on page 4: Potting Mix