Orchids are commonly grouped as cool, intermediate, and warm, based on the plant's optimum night requirements (45 to 50 degrees F, 55 to 65 degrees F, and above 65 degrees F, respectively). For warm homes, consider the Dendrobium, moth orchid (Phalaenopsis), or Vanda orchids. The moth orchids grow under similar conditions to African violets, making them one of the best choices for growing indoors.
Those for intermediate temperatures, such as Cattleya and its hybrids, may need more humidity to grow well than is usually possible indoors. Cymbidum and Oncidium, while taking cooler temperatures in winter, also need high humidity and high light to grow best.
Some orchids may not bloom if the nighttime and daytime temperatures are the same. Consistently warm temperatures are good for leaf growth, but may suppress flower development.
Most orchids require relatively high light intensities and should be grown in an east or south window. However, a few will grow well under low intensity fluorescent lights. Insufficient light is the most common reason orchids don't flower. If there is too little light, the leaves become a deep, lush green. With too much light, the leaves turn yellow-green.
Orchids vary in their water requirements. The tropical orchids, which mainly are epiphytes, should be grown in a very porous potting medium such as coarse fir bark or lava rock. Place these pots in the sink and run lukewarm water through them for about 15 seconds, then allow to drain for about 15 minutes. Terrestrial types, rooted in soil, require a well-drained growth medium. One of my favorite orchids, which is easy to grow in soil indoors in the north and lasts for many years, is the Jewel orchid (Ludisia). Another popular terrestrial orchid, easy to grow indoors, is the lady slipper (Paphiopedilum).
Watering and fertilizer frequency depends on orchid, and the medium in which they are potted. Most orchids growing in bark cannot survive prolonged drought and should be watered often. However, some require a "dry season" of six to eight weeks during which watering is reduced but not stopped. This "dry season" must occur immediately after the current growth matures and is often necessary to initiate future flowering. Some Dendrobium and Oncidium orchid species are in this group.