Water them thoroughly once or twice a week — more when it’s warmer, less when it’s cooler. Make sure the water drains completely out of the holes at the bottom of the pot. Never leave the plant sitting in water!
Over watering is probably the most common cause of failure with orchids. Orchids rot when they are soggy, and mushy or yellow leaves can be a sign of over watering. Water thoroughly, let the flowerpot drain completely, and dry out before watering again.
Tips for Proper Orchid Watering
Imagine how a tropical rainstorm would soak an orchid, drenching it for minutes or hours. A quick splash of water does not give the plant time to absorb enough. Soak your orchid in a bucket or large container so its roots have time to absorb water and fertilizer. Place it in the bowl or container and fill it to the top level of the pot. Let it sit in the water for about 15 minutes. Do not leave it soaking too long, because the roots also need oxygen.
Be sure the water drains thoroughly out of the pot! If part of the plant turns to mush or turns black, you have probably over watered or let the orchid pot sit in water. If the pot sits in a tray, empty the tray after watering. Sogginess causes rot. In their natural environments, orchids are air plants that never sit in water. Germs and other microorganisms that grow in stagnant water can cause orchid roots to quickly die.