Orchids have a reputation for being delicate flowers that must be handled extremely carefully, but that really isn't the case. Many orchids can be grown easily in the home, with very little maintenance needed after planting. As long as you pay attention to their light, moisture, soil and temperature requirements, your orchids will remain healthy and vigorous. Blossoms dropping prematurely is usually a sign that one of these elements is out of whack or a disease is present.
Orchids need relatively cool temperatures to send out flower spikes. Chill orchids at temperatures between 60 and 78 degrees Fahrenheit for three to five weeks to initiate this growth. After that, warm the orchid to between 70 and 80 degrees Fahrenheit during the bloom period. If blossoms or buds drop, it's likely that the temperature hasn't been maintained at a consistent level. Orchids do not like big temperature swings.
If temperatures are consistent and flowers are still falling off, consider where the orchid is sitting. Move it to a new location if it's anywhere near a gas stove or an area where someone has been smoking. Outdoor orchids near garages or an area where cars are started can also be a problem. Fumes from all these sources can cause flowers to drop before they should.
Too Much/Too Little Moisture
Water orchids when the potting medium is dry, but not completely dry, running the pot under cool tap water until it drains freely from the bottom. Never let the pot sit in standing water; doing so causes rot that not only makes the flowers drop, but kills the plant. If air is extremely humid, plug in a small fan nearby to keep it moving. High humidity and still air can allow bacteria and fungus to develop, causing flowers to rot.
Fertilize orchids at each watering with 1/2 tsp. of 20-20-20 fertilizer in 1 gallon of water during the growing season, and every third watering in winter. Too much fertilizer will cause a burst of vegetative growth, but hurts the flowers, particularly during the bloom period.