Orchids

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Scientific Name

I. Botany/History

  • Family: Orchidaceae
  • Growth Habit: Most orchids in cultivation are epiphytic, growing upon trees, rocks, and decomposing material instead of rooting into the ground. They have fleshy roots and stems that have a white coating called velamin. This coating helps to absorb water and nutrients. There are thousands of orchid species, highly variable in their requirements. Each species requires a different balance of temperature, humidity, light, water, fertilizer, media, ventilation, etc.
  • Origin: Native orchids have been found growing on every continent except Antarctica. New species are being discovered all of the time. *Development: In 1789, the Royal Botanic Gardens were cultivating 15 species. During the folling 50 years, orchid mania swept over Europe.
  • Key people: Currently, the major countries from which U.S. companies import orchids from are Taiwan, Thailand, and the Netherlands. The U.S. usually has mature plants shipped in from these and other countries for potted plant sales. Cut flower producers usually maintain their own crops, since plants are long lived and bloom seasonally. However, this seasonality of bloom lowers crop prices because certain species go onto the market in mass.


II. Uses

  • Pots: Potted orchid plants are becoming increasingly popular in nurseries and retail stores alike.
  • Cut flowers: Orchids are used by florists in arrangements, corsages, and wedding bouquets for an elegant and unique look. While orchids comprise only 8% of the market in sales of wholesale cut flowers, this still earns them a place in the top 10.
  • Bedding plants: Orchids are used as bedding plants in tropical areas.


III. Propagation

  • Sexual: This is usually done through seed embryo culture, because orchid seed is very minute and devoid of stored food for seed germination. Orchid and fungi have a symbiotic relationship during germination: certain fungi will infect orchid seeds and help convert complex starch to simple sugars, which serves as an energy source for both organisms. Studies have been done on different strains of fungi to determine which produce the highest germination rates for different orchid species. Seed embryo culture usually takes place in a lab, where seed is placed in a small, clear, covered container ontop a base containing nutrients and beneficial fungi. Though an orchid plant can produce thousands of seed, in nature only a few find appropriate conditions in which they can survive. However, using current seed embryo culture techniques usually produces a high germination success rate.
  • Asexual: Usually done when trying to preserve a speciman, such as in conservatories; not for mass propagation. Orchids can be asexually reproduced in a few ways. Division is done by separating pseudobulbs into sections with 2-3 nodes each. Occasionally, a bud will give rise to a young plant at the top, the side of a psuedobulb, or cane. Top cutting is done when a plant becomes leggy; new roots will develop readily. Monopodial orchids can be propagated by tip cuttings. Recently, some terrestrial hardy orchids have been propagated in vitro.


IV. Growing/Flowering

  • Light - (photosynthesis, photoperiodic responses): There are both sun-loving and partial shade orchids. Generally, most orchids prefer indirect or filtered light. The rule of thumb is to provide as much light as the leaves can take without burning, usually 50% shading. Orchid plants which receive enough light have short, plump stems with bright green leathery leaves. Those receiving too much sunlight are yellowish, stunted, and even scorched. Those under too much shade have darker green, soft and succulent leaves with thin, spindly stems.
  • Temperature (recommended/necessary for different growth stages or growth regulation): There are 3 temperature categories of orchids: Warm species prefer day temperatures up to 90°F and 65°F for a minimum night temperature. Intermediate species prefer 80°F days and 60°F nights. Cool species prefer 75°F days and 55°F nights. Most orchids, however, require a lower night temperature for both strong growth and often to initiate bloom.
  • Water: More orchids are killed by overwater rather than underwatering. Overwatering leads to root rot and many other diseases and pests (see Disorders). Water as media approaches dryness, preferrably in the mornings on sunny days. Clean water with a pH around 7 is best, but most orchids will tolerate a pH between 5 and 8.5. Watering with lower or higher pH or with high levels of dissolved minerals can prevent nutrient uptake. Orchids prefer high humidity, so it is helpful to mist regularly or use a fogger as long as there is good air circulation and ventilation.
  • Nutrition: Most species are light feeders, generally give 50-100 ppm nitrogen 3X weekly. Use higher levels in the spring during rapid growth or with Phalaenopsis species, which should be given 200 ppm N. Calcium, magnesium, and micronutrients are usually not added to standard fertilizer solutions. Fertigated plants should be flushed with pure water every fourth watering to prevent accumulation of nutrients. Use high phosphorus and potassium fertilizers before and during flowering.
  • Media/Potting/Planting: Usually no media is required, just support material. Most orchids are epiphytes, which are grown in fir or redwood bark, crumbled charcoal, pebbles, or on cork plaques. Other less common types of orchids are lithophytes, which grow naturally on rocks, terrestrials, which can be grown in a regular media such as ProMix or MetroMix or sand, and saprophytes, which are found growing in decaying vegetation in nature so they should be provided a media with high organic content. Media must be well drained with good circulation. Traditionally, orchids have been grown in terra cotta pots, which breathes better than plastic and sometimes has holes in the sides. However, terra cotta also has many disadvantages, so orchids are now more commonly produced in thin plastic pots. Open baskets of wood or cork mounts are also used.
  • Atmosphere: Most require high humidity or daily misting for proper water intake. Low humidity can cause buds to become stuck in sheaths and prevent vegetative leads from emerging, causing wrinkled leaves. Contrarily, fresh air and good circulation are also vital for orchid production. Leaves should move gently in a light breeze.
  • Growth Regulation (chemical, environmental, etc.): No growht regulation is used in cut flower production. Growth retardants or DROP is sometimes used to control height of inflorescences in potted plants to ease transportation and marketing constraints.


V. Special Considerations - (special timing or growing techniques, idiosyncraces, etc.): Some orchids are photoperiodic for bloom- they can be short-day or long-day, depending on the species. Others are day-neutral. Because orchids are so diverse, it is imperative to thoroughly research each species being cultivated.


VI Disorders Most of the pests and diseases listed can be prevented by providing good air circulation and using sterile equiptment and supplies. Control or eradication is hard or even impossible in many situations. Promote good air circulation by not spacing plants too close. Prevent water splash from pots when irrigating and use a hot or disinfected cutting tool when dividing or harvesting flowers to control spread of disease.

  • Insects:

Aphids: spray with malathion.

Black Twig Borer (Dendrobium beetle): prevent with insect screening, spray adults with carbaryl.

Fungus Gnats: Monitor with yellow sticky cards. If more than a few are present on cards, Bt or predatory mites are effective control. Gnatrol is a true-fly specific Bt, so it does not affect caterpillars.

Mealybugs and other Scales: Lightly scrub off using a toothbrush dipped in malathion.

Thrips: Spray with malathion.

Mites: Increase humidity or shower plants. Predatory mites are also effective.

Shore Flies: These do not eat the plant or flowers, but spread detrimental fungal spores. Best to prevent by controlling algae growth. Yellow sticky cards can also be used to monitor.

Cockroaches: Dust plants, pots, and surrounding area with diazinon or Sevin.

Slugs and Snails: Dust with metaldehyde


  • Diseases

Botrytis petal blight: Flowers become spotted, then rot. Avoid wetting the flowers during irrigation.

Pythium rot: Soak in natriphene solution.

Phytophthora: Prevent by ensuring good media drainage.

Erwinia: Sunken dark lesions appear on foliage. Prevent spread by disinfecting equiptment and apply a bactericide.

Pseudomonas: Avoid overhead irrigation. Control with bactericide.

Viruses: Dozens affect orchids. Symptoms include blotches or black spots or streaking in foliage. Cannot be cured, so best to destroy diseased plants.

Rusts: Best to destroy or isolate affected plants.

Black Root Rot: Plants go through yellowing and general decline in health. Prevent by using sterile pots and media.

Southern Wilt


  • Physiological

Water stress and high temperatures can both cause flower abortion. Temperatures below optimal can result in malformed flowers, short internodes, and flower abortion. Phalaenopsis species may become vegetative after inflorescenses are formed if temperatures at or above 77°F are not maintained during flower production.


VII. Marketing and Grading

  • Areas of production in U.S.
  • Specific dates or holidays if applicable


VIII. Postharvest Handling Cut orchid flowers often do not open properly with floral preserves; therefore, flowers of many cultivars should not be harvested until 3-4 days after opening. This includes species of Cattleya, Cymbidium, Paphiopedillium, and Phalaenopsis. Dendrobium species can be cut 1-2 days before opening without problems.

Flowers are very sensitive to ethylene levels. Anti-ethylene agents such as silver thiosulfate or 1-methylcyclopropene should be used. Pollination also induces natural ethylene production by the plant, so prevent pollination with insect screening. Faulty heaters can also contaminate air.

For cut flowers, place individual flowers or inflorescences in water tubes and pack with wax paper. Prevent cold injury by holding flowers at temperatures above 50°F. Many companies have special refrigerators for this.

Potted plants have too much variation between species and cultivars to give any general requirements.


IX. Cultivars Far too many to list; hundreds are introduced each year.

X. References

American Orchid Society. http://www.aos.org. Last accessed on March 3, 2006.

Dole, John M. and Harold F. Wilkens. Floriculture: Principles and Species. 2nd Ed. Pearson Education, Inc. New Jersey, 2005.