More orchids are killed by incorrect watering than by any other mistake. There are two separate components to watering: when and how. Most orchids grown by hobby growers are epiphytes, growing on trees above the ground where the light is more plentiful. Because these plants are adapted to having their roots exposed to light and air, in addition to water orchid roots need air. The central core of an epiphytic orchid root is covered with a spongy material called velamen, which is designed to store water. When this spongy material stays wet too long, the central core suffocates and begins to rot. Once the roots rot, the plant can no longer take up water properly and many other problems begin. At worst, root rot will spread upward into the rhizome and cause the death of the plant. In other cases, the loss of roots prevents the plant from absorbing sufficient water to maintain the plant in good condition and the leaves will take on a wrinkled appearance. Unfortunately, the symptoms of overwatering and underwatering are superficially similar and the tendency is to increase watering rather than inspect the roots. Overwatered roots will be brown and mushy while those on underwatered plants will be white or gray and dry. Let us look first at when to water.
WHEN
Orchids should be watered just as they dry out. This rule applies to all orchids, with slight variations depending on whether your plant has pseudobulbs (thickened stems designed to store water). Orchids such as cattleyas and oncidiums should be allowed to dry completely between waterings while orchids such as phalaenopsis and vandas that have no water storage organs should be watered just before dryness occurs. For vandas, this may mean daily watering during the warm summer. Vandaceous orchids, properly watered, will have actively growing root tips at all times. If the root tips on your plants dry up and seal over, you are not watering often enough. There is unfortunately no magic formula, i.e., water a plant in a 6-inch (l5 cm) pot every seven days and you will be trouble-free. This is because your growing area is different from anyone else’s. Humidity, air movement, potting medium (type and age) and light levels all play a role.
Inserting a skewer, chopstick, sharpened pencil, or your finger will help you determine whether the medium is dry enough to water. When many grains of organic matter stick to the skewer, moisture is adequate for an orchid that does well when kept evenly moist. For orchids that require continuous moisture, it is time to water.
HOW
Knowing how to water is just as important to proper culture as when to water. When orchids are watered, they should be watered copiously. Water should be provided until it runs freely from the drainage holes. This serves several functions. First, thorough, copious watering is necessary to soak the potting medium. In addition, thorough watering helps to flush away the salts that naturally accumulate in the potting medium from the dissolved salts in our water supplies and the fertilizers applied for good growth. Also, this is your opportunity to examine how the potting mix behaves. If you cannot pour water rapidly through the pot, the potting mix is too dense, and you risk starving the roots for air. If you see finely divided material that looks like coffee grounds in the water coming from the drainage holes, your potting mix is breaking down and it is time to repot into fresh medium. At a minimum, try to thoroughly water your plants at least once a month. Finally, a couple of notes about mounted plants and plants grown in baskets without additional potting medium. First, avoid dunking these plants in buckets of water. This practice easily spreads diseases. If one plant has a disease, all those dunked in the same bucket of water will have been exposed. Also, two short waterings a few minutes apart are much more effective than one long watering. Once water runs off the plant, the roots will have absorbed essentially all they can at that time, and excess water just runs off to the ground. The proper technique is to water plants and then a few minutes later water them again, always beginning with the first plant watered. This allows time for the roots of the last plant watered to finish absorbing water before they are wetted again.
WHEN TO WATER
To determine when a potted orchid is almost dry:
1) The surface of the potting mix will appear dry.
2) Dry pots will feel lighter when lifted.
3) Clay pots feel dry.
4) A wooden stake or skewer inserted into the potting mix will come out almost dry.
If in doubt, a finger inserted into the potting mix is perhaps the best tool for determining the moisture content of the potting mix. It will cause no harm to the plant. And remember, fresh potting mix will always dry out faster than the old medium.
[1] An overwatered orchid has a poor root system and shriveled pseudobulbs. The potting mix is dark and broken down from being kept too wet. The short brown roots are characteristic of root death. To save the plant, repot in a fresh mix in the smallest possible pot, reduce watering, and keep the plant in a humid, shady location.
[2] Yellowing growth and shriveled foliage signal root loss caused by overwatering.
