Growing Moth Orchids in South Florida
Phalaenopsis (fail-eh-NOP-siss), the moth orchid, is perhaps the best orchid for growing in the home, and is also a favorite with greenhouse growers.
Well-grown plants can flower often, sometimes with a few flowers throughout the year, though the main season is late winter into spring. Average inside home temperatures and conditions are usually sufficient.
Flower stems on certain hybrids can be forced to re-bloom by cutting the tip off after the initial flowering, although only healthy plants should be induced to flower repeatedly.
Culture for Doritis, a related genus thought by some to be synonymous with Phalaenopsis, and Doritaenopsis, a hybrid between the two genera, is the same as for pure Phalaenopsis.
Here’s what you need to grow Phalaenopsis, Doritis, or Doritaenopsis:
Moth Orchid Light Levels
Light is easy to provide for Phalaenopsis. They grow easily in a bright window, with little or no direct sun.
An east window is ideal in the home; shaded south or west windows are acceptable in southern climates. In overcast, northern winter climates, a full south exposure may be needed.
Artificial lighting can easily be provided. Four fluorescent tubes in one fixture, supplemented by incandescent bulbs, should be placed 6 to 12 inches above the leaves. If you want to use modern LED fixtures, a bit of experimentation will be required to determine appropriate light levels. Turn the lights on for 12 to 16 hours a day, following natural day length.
In a greenhouse, Phalaenopsis need shade: 70% to 85%, or between 1,000 and 1,500 foot-candles, is recommended. No shadow should be seen if you hold your hand one foot above a plant’s leaves.
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Moth Orchid Temperature Needs
Temperature for Phalaenopsis should usually be above 60 degrees F at night, and range between 75 F and 85 F or more during the day.
Although higher temperatures force faster vegetative growth, higher humidity and air movement must accompany higher temperatures. The recommended maximum temperature is 90 F to 95 F.
Night temperatures as low as 55 F are desirable for several weeks in the autumn to initiate flower spikes. Fluctuating temperatures can cause bud drop on plants with buds ready to open.
How Frequently Should I Water My Moth Orchid?
Water is especially critical for Phalaenopsis. Because they have no major water-storage organs other than their leaves, they must never completely dry out. Plants should be thoroughly watered and not watered again until nearly dry.
In the heat of summer in a dry climate, this may be every other day; in the winter in a cool northern greenhouse, it may be every 10 days. To prevent rot, water only in the morning, so that the leaves dry by nightfall.
Moth Orchid Humidity Control
Humidity is important to Phalaenopsis—it’s recommended to keep humidity between 50% and 80%.
In humid climates, such as greenhouses, it is imperative that the humid air is moving. Leaves should be dry as soon as possible, and always dry by nightfall.
In the home, set the plants on trays of gravel, partially filled with water, so that the pots never sit in water.
How Often Should I Fertilize My Moth Orchid?
Fertilize on a regular schedule, especially if the weather is warm, when the plants are most often growing.
Where bark-based media are used, twice-a-month applications of high-nitrogen fertilizer (such as 30-10-10) are appropriate. Otherwise, a balanced fertilizer is best.
When flowering is desired, a high-phosphorus fertilizer (such as 10-30-20) can be applied to promote blooming.
Some growers apply fertilizer at one-quarter strength with every watering; this is best for warm, humid conditions. When it’s cooler, or conditions are overcast, fertilizer should be applied twice per month at weak strength.
Potting a Moth Orchid
Potting is best done in the spring, immediately after flowering. Phalaenopsis plants must be potted in a porous mix.
Potting is usually done every one to three years. Mature plants can grow in the same container until the potting medium starts to decompose, usually after two years. Root rot occurs if plants are left in a soggy medium. Seedlings usually grow fast enough to need repotting yearly, and should be repotted in a fine-grade medium. Mature plants are potted in a medium-grade mix.
To repot, remove all the old medium from the roots; trim soft, rotted roots; and spread the remaining roots over a handful of medium in the bottom of a new pot. Fill the rest of the pot with medium, working it among the roots, so that the junction of the roots and the stem is at the top of the medium.
This article was authored by Ron McHatton, Ph.D., and originally appeared in the Winter 2018 edition of The Tropical Garden. Minor changes from the print version of this article were introduced to improve readability in a digital format.