As the days get shorter and the light level for your orchids is reduced, water requirements are also less. Be sure that you check your plants before watering at this time of the year to prevent over watering and the consequent rotting of roots. Use a bamboo skewer to check whether the medium several inches down in the pot is still damp before watering. A general rule of thumb is that rather than watering twice a week, water once a week.
Check light levels indoors
Make sure that your orchids, either indoors or in a greenhouse, are receiving adequate levels of light. Indoor growers may lose some of their light as a result of the movement of the sun during the winter. Take the time to check out the number of hours your orchids are receiving light to make sure it is enough. If not, consider adding grow lights to provide 6-12 hours of good light, this is especially important in the more northern latitudes.
Remove shade cloth on greenhouses
During summer months it is generally necessary to add shade cloth to greenhouses to reduce the amount of light and heat reaching your plants. By late fall the intensity and amount of daylight has been considerably reduced and shade cloth should be removed to provide adequate amounts of light. Be sure to rearrange your plants so that plants that had been receiving less light under the shade cloth are moved to shadier locations.
Use Fans for adequate air circulation
Winter is a time when many fungus and rots will attack your plants. They grow wildly under high humidity and poor air circulation conditions. Be sure to water in the mornings so that all plant surfaces have a chance to dry during the day. Keep adequate air circulation going at all times. If you think you need to add some, get one of those tiny clip-on personal fans and direct the flow toward your growing area.
Provide adequate humidity
Especially during heating seasons in home environments, it is hard to maintain adequate humidity around your orchids. Consider grouping your plants and providing a humidity tray below your plants. Grouped plants help create their own humidity. I recommend using the “egg crate” type of tray rather than gravel with water because it is too easy to rot roots with the gravel tray method.
Check your temperature differential
Especially this year when all of us are going to be very careful with winter heating due to the high price of oil and electricity, take the time to make sure that your orchids are getting some solar heat to get the day time temperature at least in the 80s. They will not grow well for you in a constant 65 to 70 degree environment. You may have to move your plants to a window with more direct sun to accomplish this. If you have installed artificial lighting to increase light, this may be enough to provide the warmth your plants