I. OVERWATERING: Often cited as the most common problem with orchids. Over watering results in psuedobulbs (and leaves, if succulent) that are shriveled and growing slowly or not at all. Inspect the roots and you will find evidence of rot. The treatment to correct this problem, is to reduce watering or to repot if the medium has decayed. Keep the plant shaded in a humid area until new roots become established. Sometimes this condition is the result of planting in a pot that is too large and in which the medium has begun to decompose. Again, the solution is to repot, this time into a smaller pot, using fresh medium. Never allow an orchid to sit in water for long periods of time. Also, don't water from the faucet unless your variety requires an excess of water.
II. UNDERWATERING: Possibly the second most common problem with orchids. Under watering has symptoms exactly the same as over watering- with one important exception: The roots will be firm and white when you inspect them. The treatment in this situation is to water the plant several times in succession until the medium is soaked. The psuedobulbs should plump up in day or two. In the future, water more frequently. However if waiting to water an orchid until it has dried out completely, the roots may not be able to take up moisture. Frequent watering can lead to root rot.
III. OVERFERTILIZATION: this condition can occur from to frequent applications or from haphazard measuring. Symptoms of over fertilization include leaf edges and tips that are burned and roots that are withered. Treat by leaching out the fertilizer by pouring several gallons of plain water-deionized if you can find it-through the growing medium. ¼ to ½ strength of a fertilizer is usually adequate, never use any fertilizer at full strength.
IV. SCALY OR POWDERY WHITE MINERAL DEPOSITS: Evidence of this is found on the rims and exterior walls of a pot and on the surface of the medium. These deposits indicate that your water contains high concentrations of minerals. Leaf tips may show signs of being burned by excess salts, and new growth may be stunted. The solution: pour several gallons of plain or deionized water through the medium to leach salts, or repot the plant. When you water, do so thoroughly over the entire surface of the growing medium, not in one spot alone. If your water is extremely hard, mix it with the deionized water or rainwater to reduce the concentration of minerals.
V. TOP-HEAVY PLANT IN SMALL POT: An obvious visual clue of yellowing tells when it's time to divide and repot an orchid plant first. The less obvious symptoms include gradual, even yellowing of the leaves, the oldest affected. There may be an overall dullness about the appearance of the foliage. New growth likely will be stunted and the psuedobulbs will extend out over the edges of the pot, or be packed to the point of beginning to grow on top of each other.
VI. SUNBURN OR TOO MUCH LIGHT: Sunburn is indicated by scorched blotches on leaves and exposed surfaces of psuedobulbs. In general, overall yellowing of the plant occurs. The flower buds may be deformed. Provide less light and more shade. A lower daytime temperature, or in extreme cases increased humidity and therefore good air movement prevent heat buildup.
VII. TOO LITTLE LIGHT: Inadequate light is indicated by foliage that appears dark green and healthy but remains flowerless. Increasing the light gradually over a period of a month should help. If the plant is growing under fluorescent lights, increase the number of lamps, or the hours they are in use. Replacing also helps if they have been in constant use for a year or more. Raise the plants so they are closer to the light. However never have them under light for more than 14-16 hours a day.
VIII. AIR POLLUTION: Certain types of air pollution can bed a problem if not detected and corrected. Gases in the air -ethylene from ripening fruit, sulfur dioxide from smog, and other gases from pilot lights, stoves, or heaters-can result in flower damage ranging from drying and discoloring of the tips of the sepals to rapid wilting of the flower. Buds may falloff. Sheaths may yellow and dry before buds appear. Don't leave flowering orchids in a closed room with ripe apples or hyacinth flowers; both give off large amounts of ethylene. Improve ventilation and make sure gas appliances are properly adjusted.
VIIII. BUD DROP: Bud drop can be caused by temperature fluctuations, reduced humidity, or a change in environment-as well as air pollution. A large swing in temperature in a brief period, for example 20oF or more, is one of the most common causes of bud drop. Also, moving an orchid in bud from ideal light, moisture, and temperatures, such as in a greenhouse, sunroom, or light garden, to a relatively dark, dry, home situation may also results in buds shriveling and dropping. It's better to wait until flowers have opened before moving plants.
IX. PLEATED LEAVES: this condition occurs among orchids having relatively thin leaves, miltonia for example, and orchid plants that in general are weak, stunted, and shriveled. Pleated leaves are a signal of inadequate watering. If the growing medium dries too much between waterings, roots never have a chance to become sufficiently established to boost vigorous growth. All they are doing is surviving. Water more often and be consistent. Mark your calendar if you have to, then keep appointments with your orchids. Another cause for pleated leaves and overall lackluster plants is too little of the good things orchids need, namely, a moist atmosphere and fairly strong light. It may be that you need to add a cool vapor humidifier to your growing area during that time of the year when the heating system is being used, along with some fluorescent or other supplementary lights.