Many orchids require a rest period in winter. As days get shorter and temperatures drop in the autumn, cut back on water and fertilizer. In the wild, dormancy occurs naturally when rains decrease or temperatures drop.
Do not let the plant dry out completely, and continue to maintain moderate humidity around the leaves. During this time you may be able to water the orchid as seldom as once or twice a month.
Phalaenopsis and Paphiopedilum do not go through dormancy. Some orchids, such as Cattleyas and Oncidiums, have a swollen bulb at the base of each leaf, called a pseudobulb, where they store water. Plants with pseudobulbs need winter dormancy.
Some orchids may grow in autumn or winter, starting new leaf growth, flower spikes, and roots when temperatures dip and days shorten. You can still cut back a bit on water and fertilizer.
Nighttime also represents a period of dormancy for plants. Some orchids need a certain number of consistent hours of darkness each night for chemical processes to occur. Other orchids are not bothered by artificial light at night, and may enjoy the extra energy. If an orchid refuses to bloom, give the plant the same number of uninterrupted hours of darkness each night, and it may flower.