Orchid Cultural Requirements

By the Plant Information Specialists

·· Orchids ··


Orchid Cultural Requirements


The Orchid family, Orchidaceae, is one of the largest of all flowering plant families, with plants growing in many different habitats. Most orchids are epiphytes which anchor and grow on other plants but do not have roots in the soil; or terrestrials which do anchor and grow in soil. There are two main growth habits of orchids: sympodial growth as exhibited in Cattleya, and Paphiopedilum and monopodial growth as displayed in Phalaeonopsis and Vanda. Sympodial types produce creeping stems with storage organs (pseudobulbs) which give rise to leaves and flowers. Monopodial orchids have a main stem which grows upwards and produces flowers between the leaves at the leaf axils.

Since the mid 1800's, more than 100,000 orchid cultivars have been developed and orchids can be found to suit almost any growing condition.

Successful orchid culture is the result of imitating an orchid's natural habitat as closely as possible. All orchids need appropriate light, temperature, humidity, soil moisture, nutrients, air ventilation, potting medium, and maintenance. Here are some requirements for success:

Light

Before choosing an orchid, be sure to determine if it will grow favorably under your light conditions. Some flourish in subdued light, while others require more sun. Sources of light include natural sunlight and artificial illumination from incandescent or fluorescent fixtures. Light intensity is measured in units of foot-candles. With the use of a light meter you can directly measure the light exposure of the potential growing area. A bright, sunny day out of doors may measure as much as 10,000 foot-candles, while a south-facing window may be about 5,000 foot-candles.

Orchids which have too little light will look lanky and not bloom properly, while those plants receiving too much direct sun will have sunburned foliage. Vanda and Cattleya have high light requirements: between 2,000 and 3,000 foot-candles. Medium light orchids like Miltonia and Oncidium require between 1,500 and 2,000 foot-candles. Low light Phalaenopsis and Paphiopedilum grow well at around 1,000 foot-candles.

Artificial lights can be used to successfully grow orchids. A minimal system would include four 48-inch length fluorescent tubes. Two of these should be warm, which emit red light and the other two cool, which emit blue light. You can also use four special plant growing light tubes, which contain both the warm and cool spectrum. Be sure the growing bench beneath the light fixtures is deep enough to place the orchids about 4 to 6" below the fixture.

Temperature

Most orchids need a distinct fluctuation between day and night temperatures to successfully produce flowers. In addition to measuring the light intensity at a potential growing location, it is practicable to measure the day/night temperatures with a thermometer. After you know these temperatures, you can choose an orchid, which falls into one of the three most common classifications: high temperature, intermediate temperature, or low temperature. Warm-growing orchids like Phalaenopsis and Vanda prefer day temperatures between 75 to 85º F, with night temperatures between 65 to 70º F.

Orchids such as Cattleya, Dendrobium, and Oncidium prefer to be grown under intermediate temperatures or 66 to 75º F during the day and 55 to 65º F at night. Cool-growing orchids such as Cymbidium prefer night temperatures with lows around 50º F and day temperatures between 60 to 65º F. Many orchids grow comfortably in the intermediate range.

Humidity

Humidity in the air is just as necessary as moisture in the soil. A minimum of 40% relative humidity is required to grow most orchids, although some require higher humidity. In homes and apartments both heating in winter and air conditioning in summer remove a lot of moisture from the air. Supply extra humidity with humidifiers or group plants on a gravel-lined tray that is filled with water to increase air moisture through evaporation.

Watering

Orchids are killed more often by the common mistake of over watering than anything else. Certain orchids like Cattleya and Oncidium need to be watered when the potting medium has almost dried out. Others like Dendrobium, Cymbidium, and Paphiopedilum, like to have the medium kept evenly moist.

When it is time to water, place the plant in a sink and allow the water to soak through and drain out completely. It is best to use tepid water, as it will help to dissolve fertilizer salts and not shock the plants.

Nutrients

Since most orchid potting mediums are not composed of real garden soil, generally orchids flower best with bi-weekly feedings of dilute, water-soluble fertilizer. Remember to drench with plain water once a month.

Ventilation

The high humidity in tropical areas is often accompanied by gentle and constant air movement. Stagnant, humid air is as detrimental to orchids as are cold drafts. Air movement is essential as it evaporates moisture on leaves and stems and helps protect plants from the spread of disease.

Potting Mediums

A medium size fir bark seems to be preferable for most commonly grown orchid plants; especially ephiphytic orchids. Terrestrial orchids like Paphiopedilum prefer finer bark mixes. Commercially prepared orchid potting mixes are typically a combination of coarse peat moss, redwood fiber, charcoal, osmunda fiber, or tree fern fiber. Be sure to use only quality orchid potting mixes and never substitute landscape mulches for orchid potting mediums.

Maintenance

With orchids, cleanliness is of great importance. Wash orchid leaves occasionally with soapy water to reduce the harmful effects of excess debris and minor insect infestation. Since orchids are susceptible to viral diseases, use gloves when handling them and/or wash hands often between handling. When cutting stems always use tools sterilized in a 10% bleach solution and/or alcohol or use a clean, single-edged razor blade.

When orchids outgrow their pots, they should be repotted. This is best accomplished every other year when new growth is beginning. Try to avoid transplanting in mid-winter and in the heat of summer. Usually plants in bud and flower prefer not to be transplanted. It is important to remove as much of the old potting medium from the roots as possible by shaking or rinsing the roots under water. Any rotting roots need to be removed immediately with sterile tools. Orchids can be propagated by division at this time as well.

Troubleshooting

From time to time various symptoms appear on orchids which result from pests, diseases and/or the result of inadequate growing conditions. As with many houseplants, certain common pests can attack orchids. These include red spider mites, aphids, mealybugs, scale, and snails. These must be carefully monitored and removed with a cotton swab dipped in alcohol or sprayed with an appropriate insecticide.

Over watering reduces air circulation around the roots leading to dieback from root rot. If a plant looks off-color, yellow, and weak, shake it out of the pot and check the roots for signs of root rot. Root color should be beige or white; black roots indicate rotting. Save the plant by removing the rotting roots, dividing, and repotting in fresh potting medium.

Orchid Selection

For beginners, the orchid cultivars of Phalaenopsis, Paphiopedilum, and Cattleya are relatively easy to grow. These have been selectively bred to be vigorous under indoor conditions.

The American Orchid Society, with many local chapters, offers excellent information on the specifics of orchid culture. Please contact them directly:

American Orchid Society
16700 AOS Lane
Delray Beach, FL 33446-4351
(561) 404-2041

Orchid Cultural Requirement Chart

Orchids by Genus
Winter Night Growing Temperature
Summer Day Growing Temperature
Light Growing Preference*
Relative Humidity Preference
  WARM WARM    
Phalaenopsis 65 to 70° 90° Maximum Low 50 to 60%
Doritis 65 to 70° 90° Maximum Low 50 to 60%
Vanda 65 to 70° 90° Maximum High 70%
  INTERMEDIATE INTERMEDIATE    
Paphilopedilum 55 to 60° 80 to 85° Maximum Low 40 to 50%
Oncidium 55 to 60° 80 to 85° Maximum Medium 40%
Miltonia 55 to 60° 80 to 85° Maximum Medium 40%
Cattleya 55 to 60° 80 to 85° Maximum High 40%
Dendrobium 55 to 60° 80 to 85° Maximum High 40%
  COOL COOL    
Odontoglossum 50° 65 to 70° Maximum Medium 50%
Cymbidium 50° 60 to 65° Maximum High 50%

*Note: Light Growing Preference: High: 2,000 to 3,000 Foot Candles, Medium: 1,500 to 2,000 Foot Candles, Low: 1,000 Foot Candles

·· Orchids ··



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