From : The University of Georgia College of Agricultural & Environmental Sciences
Cooperative Extension Service
Paul A. Thomas, Extension Horticulturist-Floriculture
Orchids belong to the most diverse family of plants known to man. There are over 880 genera, 28,000 species and well over 300,000 registered cultivars currently documented. These numbers only begin to tell the true story behind the evolutionary success of modern day orchids. Orchids are the most rapidly (genetically) changing group of plants on earth and more new species have been discovered over the last few thousand years than any other plant group known.
Orchids are also one of the most adaptable plant groups on earth. Some Australian orchids grow entirely underground, and many tropical jungle orchids grow in the upper branches of trees. Tundra, rainforest, mountain, grassy plain, desert and swamp environments contain numerous orchid species.
Orchids produce seed pods with literally hundreds of thousands of seed that are released and scattered by the wind. Orchid seeds must establish a symbiotic relationship with a special fungus to survive its first year of life. The fungi gathers water and minerals for itself and the seedling, and the seedling shares its sugars from photosynthesis with the fungus. Only one or two orchid seeds will ever germinate and survive on that perfect crevice or depression that is both moist and has the fungus present. Even then, its chances to survive in the wild long enough to bloom are slim.
To avoid this problem, greenhouse growers sow orchid seeds on moist, sugar-rich, sterile agar, or they cut out growing clumps of orchid cells and place them on the agar. These techniques allow many hundreds of orchid plants to survive to maturity. New and improved hybrids can be mass produced rapidly. This is important as orchids are very slow growing. Many orchids take five to seven years to mature to flowering. You can see why breeding three or four orchid generations could span a person's lifetime just to get one new hybrid propagated sufficiently for sale.
Classification
All orchids belong to the Orchid Family, Orchidaceae (or-Kid-ACE-ee-ee). Orchids are divided into two basic growth types: monopodial and sympodial. Monopodial orchids have a central stem which grows continuously from the tip. Flowers are produced from the stem between the leaves, usually alternately from side to side. Phalaenopsis orchids are a good example. Sympodial orchids, such as cattleyas, laelias and paphiopedilums, possess a rhizome which sends out a shoot. This develops into a stem and leaves and eventually produces flowers. In time, from the base of this growth, a new shoot develops and so on in a continuous cycle. The buds are often, though not always, protected by a sheath.
The mid section of stems of sympodial orchids are often expanded into water-storage organs called pseudobulbs. These vary greatly in size and shape, ranging from tall and pencil-thin to bulbous and onion-like. The leaves vary too, some being soft and folded like a fan, others thick and leathery. The roots of epiphytic orchids have an outer layer or corky cells called velamen, which protects the thin, living cortex within. These adaptations allow orchids to absorb water and nutrients rapidly from raindrops, but protect roots, stems and leaves from water loss during dry periods. Most orchids are adapted to conserve water and should be cared for as such.
Orchid Cultural Requirements
Growing Medium
There are many different types of orchid potting medium used in orchid culture. The overall consideration is to provide structural support for the orchid roots, but also to provide lots of air spaces between medium particles. Many orchid plants are grown in osmunda fiber. This fiber comes from the roots of the Osmunda fern that is native to Australia and the Pacific. The tough, wiry fibers break down very slowly and is an ideal potting medium. Fresh pine bark is also a popular medium but is usually mixed with other amendments before use. Both materials are sometimes mixed with peat and perlite or vermiculite. Some orchids are even grown in pebbles mixed with bark. Most orchid roots are adapted to being exposed to air and harsh conditions, but cannot tolerate being wet for more than a day or two.
Orchids grow slowly compared to houseplants. However, most orchids need to be repotted about once every two years. To pot an orchid, the pot is filled about two-thirds with orchid potting medium, then the plant is set in the pot with its roots spread out. The growing tip either centered (monopodials) or placed two fingers from the pot rim (sympodial). Then additional media is packed tightly around the plant to hold it in place. You should be able to turn the pot upside down without the orchid or medium falling out. Practice will insure successful repotting. When the plant outgrows the pot by extending the new shoots over the edge, usually about every two years, it is time to repot.
Light
The ideal place in the home for growing orchids is a bright window, free from drafts, where your plants receive indirect sunlight both morning and afternoon. (A south window is best.) In winter, give orchids all the light possible. Light intensity should be between 1500 and 2000 foot candles the equivalent to a bright south-facing window. With extra large windows or especially intense sunlight, the light may be adjusted downward by moving plants 18 to 36 inches from the window. Plants in the home require a greater light intensity because they receive light from only one direction, while in a greenhouse they receive light from many sides.
Many orchids can be grown in a greenhouse or outdoors. All will require partial shade. Therefore, it is best to shade the section of the greenhouse you intend using or else grow them in an area that you have already shaded for foliage plants or African violets. Dendrobium Oncidium and Vanda will grow best in 20-30% of normal outdoor light, whereas Phalaenopsis-type orchids require only 10- 15 % of normal light.
Artificial Light
If you have neither a greenhouse nor the proper windowsill conditions, fluorescent lighting provides good results. You can grow and flower many types of orchids in the darkest basement or shadiest apartment with the addition of just one shop light. Most orchid hobbyists find having at least four 36" or 48" fluorescent tubes provides excellent light levels. Each group of orchids (primarily those with low to medium light requirements) will need a minimum of two forty-watt fluorescent light tubes hung six inches above the plants.
Keep lights on for a minimum of 12 hours per day in order to provide the minimal amount of light necessary for proper growth and flowering. If you are able to place your fluorescent light setup near a sunny window, your orchid flowering chances will increase. The best type of fluorescent tubes seem to be those designed specifically for plants.
Humidity
Potted orchid plants may be set on decorative pebbles in a water-filled tray, saucer, or other container. Evaporation of water from pebbles provides humidity. Pebbles also make the growing area more attractive, while assuring good drainage. Mist your plants with distilled water because tap water can lead to salt deposits on the leaves. A plant which is kept soaking wet invites attack by bacteria and fungal diseases. If you are able to enclose an area like a greenhouse, you will find it easier to maintain a proper humidity.
Temperature
Orchids are not as delicate and temperature sensitive plants as most people think. Most will adapt readily to conditions offered by any home or greenhouse. For growing purposes, we group orchids into three temperature classes:
The medium temperature class is represented by many Cattleyas, Epidendrums, Oncidiums, and Laelias, and most other commercially available orchids. The ideal minimum temperature is 60 degrees F nights and high 70s during the days. An occasional deviation will have no harmful effect. This group will do very well with the air, temperature, and light facilities found in the average home.
The cool class includes Cymbidiums, Cypripediums, Odontoglossums and Miltonias, and should be grown 5 degrees to 10 degrees F cooler than the medium class. These plants also require high light, so imagine cool, sunny October mornings as an example of the light and temperature that this class needs.
Warm class orchids are represented by Phalaenopsis, Paphiopedilums, Vandas, Rhynchostylus and Dendrohiums. These plants should be grown 5 degrees F warmer than those in the Medium Class. They do well in high humidity and can be grown outdoors in Georgia from late spring to early fall if shaded and protected from rain. Never expose orchids of this class to less than 45 degrees F.
During cold, freezing night temperatures, all orchid plants should be moved away from the window to provide a protective airspace against freezing. Air temperature can be 15 to 20 degrees F cooler near the windows than the room temperature.
Watering
Watering is the most important factor in orchid culture. A good rule of thumb is to water whenever the medium (osmunda fiber or bark mix) is dry. If you grow the plants in pots suspended in the air, they will dry out more rapidly than bench grown plants and will need watering more frequently. Orchids potted in bark require more frequent waterings than those in most other potting media, just as plants in clay pots require more frequent watering than those in plastic pots. Orchids may be grouped into three categories according to their moisture requirements.
Low Water Use. Cattleyas, Laeliocattleyas, Brassolaeliocattleyas, Oncidiums, Miltonias, and Odontoglossums are ephiphytes or "air rooted" orchids, with built-in "water tanks" or pseudobulbs. They should be allowed to dry out slightly between waterings so air can circulate between the epiphytic roots. Water every five days or so. In the heat of mid-summer, water may be needed every three or four days. During the short, cool days of winter, increase the time between waterings to 10 to 14 days. If you do err in watering, make sure it is on the dry side.
Moderate Water Use. Phalaenopsis, while also epiphytic are monopodial and do not have built-in tanks for water storage, but store some water in their leaves. They require watering similiar to ordinary house plants, but more frequent waterings than orchids with pseudobulbs. Water enough to keep the potting medium from becoming dry for more than a day or two.
High Water Use. Paphiopedilums and Haemeria orchids are semi-terrestrials or terrestrials (meaning "earth-rooted"). Unlike the preceding groups, they do not mind "wet feet." They like an abundance of moisture and the soil can remain damp for many days without any negative effects. Many terrestrial orchids are potted in peat based media which will naturally hold more water than the bark mixes.
Outdoor Conditions. Cymhidiums and many other orchids, such as cattleyas, can be grown outdoors during frost-free months in Georgia. They also like an abundance of moisture - but with good drainage and plentiful root aeration. However, do not plant tropical /greenhouse orchids outdoors in your garden soil. The soils are too dense to allow the roots to survive.
Fertilization
For best results, fertilize orchids with soluble plant food. When fertilizing plants growing in osmunda, bark or peat/bark mixes, use a complete liquid fertilizer with a 20-20-20 analysis, or a 30-10-10 orchid-special fertilizer. Don't fertilize more than once a month. Apply the fertilizer in place of a normal water application. It is always best to use fertilizer at 1/2 the recommended rate. Orchids are adapted to environments where nutritional levels of the soil or bark are very low. More orchids are killed because of over-fertilization and over-watering than by any other cause.
Ventilation
In greenhouses, a small fan should be run continuously to circulate the air. A window left ajar in all but the coldest of weather may also be adequate to provide proper ventilation indoors. Airconditioning may harm orchids because the air is much too cold coming out of the unit. Keep orchid plants out of cold drafts and away from heating vents.
Orchid Pests and Diseases
Orchids have few insect pests or diseases if properly cared for. It is important to have a problem identified before attempting control. Take a sample to your county Extension agent and follow recommended treatments suggested. Many disease prevention tips are provided in an orchid disease guide published by the American Orchid Society. Wiping leaves with a warm, soapy, wet cloth is sufficient to eradicate insects like mealy bugs if you have but a few plants in the house. Be careful because many insecticides can damage your orchids. Read the label to see if the pesticide can be safely used on orchids specifically. If you have questions, ask your county Extension agent.
Orchids for Hobby Growers
One of the most frequently asked Questions from the hobby grower is, "What type or variety of orchid should I grow?" Usually when you mention the word "orchid" most people immediately think of the purple-flowered Cattleyas, and rightly so as they have long been the most popular in the trade. However, the genus Cattleya contains a mere 50 species of the 28,000 known. Many, many other orchids do wonderfully in the home.
Hobby growers should try growing hybrids of Phalaenopsis, Paphiopedilum, Dendrobium, Oncidium, Vanda and Epidendrum. Phalaenopsis orchids are excellent for beginners. They may produce up to 15 or more flowers per spike. The flowers measure up to four inches across. Flowers may remain open for six weeks or longer. Frequently when a spike is cut, a secondary spike will develop on the old stalk below the original flower head, thus extending the blooming season. Phalaenopsis plants are very easy to grow.
Dendrobium hybrids are some of the better corsage type orchids. Lavender or white flowers are borne in profusion on a well-grown plant and are long lasting. They are a prolific group in that offset plantlets are frequently produced on the cane. When each offiet has produced several aerial roots, it can be cut from the parent plant and will frequently flower after one year of growth.
Oncidiums, commonly, referred to as dancing girls, are also easy to grow. These dainty yellow and brown or white and brown flowers are suitable if used alone or in combination with other orchids. Large flowered Oncidium sdhacelatum - with their yellow and brown color combination can be made into a corsage. These hardy plants flower well even under adverse growing conditions.
Vandas are becoming popular among orchid growers. The wide range of colors which includes some fairly good blues and browns and long lived flowers has added greatly to their popularity. Vandas may grow to be very large plants, sometimes 10 to 12 feet high, but they grow very slowly. A plant two feet tall may be seven or eight years old. Vandas are often grown outdoors in hanging baskets during the summer months.
A tough group of orchids is the Epidendrums. Epidendrum hybrids are becoming popular plants.
These are undoubtedly one of the easiest orchids to grow and one of the most prolific groups. The tall, thin, reed-like growths constantly put forth new plantlets. It is relatively simple to take tip cuttings having a few aerial roots. Although the flowers are small, about one inch in size, they are produced in great profusion.
Paphiopedilums are one of the best orchid groups to grow under artificial lighting. There are many spectacular hybrids available, and quite a number of species. They are not fragrant, but have very interesting and colorful "lady slipper" shaped flowers. Due to import regulations and conservation considerations, we recommend you grow only orchid hybrids so as not to promote the collecting of species from the wild.