AMES, Iowa -- Many species of orchids bloom at all times of the year. The popular moth orchid (Phalaenopsis spp.) often blooms indoors during the cold months of winter. Moth orchids are one of the easiest orchids to grow indoors. The beautiful blooms can last for months and plants can be grown and brought into bloom year after year. In this article, horticulturists with Iowa State University Extension and Outreach answer questions about caring for moth orchids.

Moth orchids grow in a coarse bark medium that is best kept evenly moist but never wet. Plants should be watered well and then allowed to dry between waterings. When ready to water, a wooden chopstick inserted into the coarse media will come out completely dry. To water, run water over the media until it wets the entire rotting media and runs out the bottom of the container. Avoid wetting the foliage. Water with copious amounts of water, since much of it will flush away.

Moth orchids purchased from retailers are often grown in coarse sphagnum moss. This material stays wetter longer than the traditional bark media but can also be challenging to re-wet when it dries out completely. Make sure that all the rooting media (whether it's moss or bark) is thoroughly wetted. Always empty saucers, trays, or outer pots and never allow plants to sit in water. Plants are susceptible to root rots and death when watered too frequently or allowed to sit in water.

Moth orchids grow best in bright, indirect light. Direct sun may actually harm the foliage. Ideal sites are east- and north-facing windows. Plants in a south window may need to be shaded with a sheer curtain. Often when moth orchids receive too much light, their leaves develop a reddish color. 

Phalaenopsis orchids will not grow or flower well in poorly lit areas. Supplement lighting can be used to provide more light when light levels from the window are not sufficient. Select high-output, full-spectrum fluorescent or LED lights and position them within 6 to 12 inches of the foliage. Keep the lights on for 12 to 16 hours each day.

Moth orchids prefer daytime temperatures of 70 to 80 degrees Fahrenheit and nighttime temperatures of 60 to 70 F. Cool nighttime temperatures of 55 to 60 F in fall help initiate flower development. Avoid exposing plants to temperatures below 55 F.

Phalaenopsis orchids require a relative humidity of 40-60%. Unfortunately, the humidity levels in most homes during the winter months are well below this range. Humidity levels indoors can be increased with a room humidifier or by placing the plant on a tray or saucer filled with pebbles and water. The bottom of the pot should be kept above the water line. The evaporation of water from the tray will increase the relative humidity near the plant.

Orchids benefit from repotting every two to three years. Over time, the coarse potting media breaks down, allowing it to hold more water and causing root rot issues. Regular repotting with fresh bark media (even if in the same size container) helps roots and plants stay healthy. Only move moth orchids to larger containers when you cannot physically fit the root mass in the container. The container size is determined by the root mass, not the size of the leaves and stems. After many years, the orchid's root system can become too large for the container, pushing the plant up and out. Repot these plants in a new, larger container with fresh potting media. 

Moth orchids typically initiate flowers in the cool temperatures of fall and bloom over the winter months. Providing all the proper environmental conditions, such as light, temperature, water and fertilizer, will allow the orchid to bloom.

Several factors may lead to a moth orchid that fails to rebloom. Address these factors to get plants to bloom again. Insufficient light is one of the primary reasons why many orchids do not rebloom. Ensure plants receive bright indirect light from a bright window or supplemental light source. Orchids that have not been adequately fertilized will not flower well. During the spring and summer months, fertilize often using a dilute solution of a balanced fertilizer. A fertilizer mixed at half or quarter strength and applied with every other or every third watering works well. Moth orchids also need several weeks of a 10-15 degree drop in temperature at night – ideally down to 55-65 F to initiate flowers. When grown indoors, occasionally this drop in temperature from day to night does not happen. Be sure to provide a temperature drop at night in the fall to trigger flowering.

Shareable photos: 1. Phalaenopsis purple. 2. Phalaenopsis white.

515-294-8953 ajsteil@iastate.edu

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