The Mystique of Tropical Orchids
Orchids have been the source of fascination and frustration to plant lovers for centuries. There’s no disputing the fact that they are some of the most astonishingly beautiful flowers in existence. Their amazing jewel-like colors and compelling scents (think vanilla, which comes from the Vanilla planifolia orchid) tantalize us. Their exotic shapes and strange anatomical structures intrigue us. The frustration lies in not understanding their cultural requirements, which differ to some extent from those of most plants. But once you grasp a few basics about orchids, you’ll see that they really aren’t difficult to grow.
Orchids are believed to have evolved around 80 million years ago. They were already ancient life forms when the dinosaurs roamed the earth 65 million years ago. With approximately 25,000 species and more than 100,000 registered hybrids, orchids comprise one of the largest and most diverse flowering plant families in existence. Within such a large family, it’s no surprise that considerable diversity exists in the colors, shapes, growth habits, and cultural requirements of its members. They can be found growing wild on every continent except Antarctica and in a broad range of habitats, including the deserts of Western Australia, remote Mediterranean mountaintops, and cloud forests of Central America. Approximately 200 orchid species are native to the United States, where they grow in every state including Alaska. But the greatest variety and concentration of orchid species come from the tropical and subtropical areas of South America and Asia.
The fascination with orchids has spawned a vast number of orchid societies around the globe. In this country, the American Orchid Society (AOS) has about 30,000 members nationwide with over 500 affiliated societies worldwide, including the local Charlottesville Orchid Society. The AOS is an excellent source for information on orchid basics and other related orchid topics.
While there is much diversity within the orchid genus, all orchid flowers share a few common traits that are unique among floral plants. Each flower is bilaterally symmetrical (the right and left halves of the blossom are mirror images) and typically has three petals and three sepals. The bottom petal tends to be highly modified forming a greatly enlarged lip, which the flower uses to attract potential pollinators. Unlike the separate structures found in other flowers, the female pistils and male stamens of orchids are fused together in a single column.
Orchids have highly specialized root systems, which are categorized as epiphytic, lithophytic, or terrestrial.
- Epiphytic – Most orchids grown as “houseplants” fall into this category. The term “epiphytic” refers to the orchids’ aerial roots, which are exposed to the warm, humid air and rain and anchor the plant in the tree canopy to take advantage of more light. The highly specialized thick, fleshy aerial roots are covered with a spongy substance called velamen. The dead cells making up the velamen layer quickly absorb water but must dry rapidly, which is why they need to be exposed to air. Otherwise, they would rot. Epiphytic orchids grow on trees or other plants for support, but they do not extract any nutrients from the host plant.
- Lithophytic – The specialized roots of lithophytic orchids are similar to those of the epiphytic species and also need to be exposed to the air. Instead of growing on trees, lithophytic orchids anchor themselves onto rocks. They extract nutrients from debris that falls into the rock cracks and crevices. Lithophytic orchids like high humidity and frequent watering.
- Terrestrial – Orchids that come from the temperate regions of the earth are generally terrestrial. They grow on the ground in leaf litter or moss on the rain forest floor but they do not extend their roots into the ground. The thick roots are shallow and covered with hairs (rather than velamen cells) that absorb water. In their natural habitat in the tropical rain forest, terrestrial orchids are shaded by the tree canopy and can tolerate lower light levels.
For purposes of propagation, orchids may be described as:
- Monopodial – Orchids belonging to this group grow from a single stem that increases in height with age. The leaves grow vertically on top of one another from a single growing point that rises from the roots. They cannot be divided to make more plants. Instead, they are generally propagated through tissue culture methods. Phalaenopsis and Vanda orchids are examples of monopodial species.
- Sympodial — Orchids belonging to this group have multiple growing points and grow horizontally, increasing in diameter with age. New growth emerges laterally from older growth. Members of this group, such as Cattleya, Dendrobium, and Oncidium, can be divided to create more orchids.
- Keiki Forming – Some orchids are capable of asexual propagation resulting in a clone of the parent plant. The clone, called a keiki (Hawaiian word for child), may be found attached to the stem or the flower spike. After a keiki develops several leaves and forms two- to three-inch long roots, it may be separated from the mother plant and grown as a seedling.
Orchids may be categorized as warm-, intermediate-, and cool-growing. Each category grows best in the temperature range assigned to it. However, there is considerable overlap among the categories. When selecting an orchid, it’s wise to follow the instructions that come with it regarding the care and temperature range recommended for that particular species or hybrid. Unless you are a serious orchid collector with the ability to compartmentalize your home or greenhouse into specific climate zones, it may be wiser to select orchids having the same or similar growing requirements.
RECOMMENDED ORCHID SPECIES FOR THE HOME GROWER
The following orchid species are generally recommended for the home grower because they adapt well to the living conditions found in most homes.
- Cattleya (Intermediate Growing) –
The queen of the orchids, the spectacular Cattleya orchid is one of the most beautiful flowers in the world. It is the orchid species customarily associated with corsages. One of the most commonly grown orchids in the home, Cattleyas are often fragrant and the flowers can last from two to six weeks. The plant requires a lot of light and prefers an east or west window or a slightly shaded south-facing window. Rather than aerial roots, the epiphytic, sympodial Cattleya has a pseudobulb, which stores water. Allow this plant to dry out somewhat between waterings.
- Cymbidium (Cool Growing) –
If the Cattleya is the queen of the orchids, the tall-growing (up to three feet) Cymbidium might be considered the king of the orchids. Cymbidium orchids are terrestrial, sympodial orchids from Asia that grow best in a fine-grain bark mix. The flower spikes contain a dozen or more blooms, some of which are scented. The flower spikes have to be staked. Otherwise, they become top heavy with the weight of the blooms. Provide as much light as possible but shade from direct sun in summer.
- Dendrobium (Cool to Intermediate Growing) –
This is a very large genus of epiphytic, sympodial orchids. Most members of this group are called Dendrobium Phalaenopsis because the shape of their flowers resemble those of the Phalaenopsis orchid. They can tolerate some sun but no direct midday sun. They do well in a west or south-facing window with diffused light (from a sheer curtain). This species grows from slim pseudobulbs, grows best when potbound, and produces offshoots (keikis).
- Miltoniopsis (Cool Growing) –
Commonly referred to as “pansy orchid” or Miltonia, this species has become very popular because of its charming, large, flat blossoms, which are available in a wide range of colors. Each flower has a butterfly-shaped design in a contrasting color in its center. It grows from pseudobulbs, which should be grown in a fine-grain bark mix. This plant needs bright light but no direct sun. It does not like temperatures above 80°F. Pansy orchids need to be kept evenly watered. Otherwise, the new leaves will begin to take on an accordian-fold appearance and will not flatten out again.
- Oncidium (Cool to Intermediate Growing) –
Commonly called “dancing ladies,” this large, diverse genus consists of more than 1,200 species. These epiphytic, sympodial orchids may be more difficult to grow than other species, but the billowing masses of predominantly yellow flowers make growing them worth the effort. Hybrids with thick leaves can tolerate more light than thinner-leaved selections. In general, Oncidiums require less humidity and less frequent watering than many other orchid species.
- Paphiopedilum (Intermediate Growing) –
This terrestrial, sympodial orchid genus is commonly known as “slipper orchid.” The flower consists of a pouch-like sac with a large showy sepal at the top. The flowers tend to be mottled with spots, hairs, and stripes. While some species have plain green leaves, other species have beautifully mottled foliage. The species with mottled leaves prefer daytime temperatures in the 80s and nighttime temperatures in the 60s. The plain-leaved species prefer cooler growing conditions with daytime temperatures ranging from high 70s to low 80s during the day and nighttime temperatures ranging from 55 to 60°F.
- Phalaenopsis (Warm Growing) –
The Phalaenopsis or “moth orchid” is a large family of epiphytic, monopodial orchids that are easy to grow and a good choice for a beginner. It’s the most popular potted orchid species because of its long, arching sprays of flowers that remain fresh for several months. It derives the name moth orchid because the long sprays of blooms resemble a flight of moths. An east-facing window is ideal for this species.
- Vanda (Warm Growing) –
This epiphytic, monopodial species produces a spray of a dozen or more flowers ranging in size from two to four inches. The flowers are sometimes dappled in appearance and come in unusual colors, including brown and blue. Vandas have large aerial roots that do not like to be disturbed by removing them from their containers. If they must be disturbed, soak the roots in water for a brief period to make them more pliable.
To grow orchids successfully, it’s important to understand their unique cultural requirements:
- Air Movement — Orchids like to have air circulating around their roots, which is why orchid pots have holes in the sides. Moving air lowers the leaf temperature and also helps prevent pests and diseases. During mild weather, move orchids outdoors where they will get lots of fresh air, resulting in more vigorous plants.
- Light – It’s important to provide the correct amount of light needed by your orchid type and species. The primary reason orchids don’t bloom is because of insufficient light indoors. Leaf color is a good indicator of light adequacy. Healthy orchid foliage is typically medium green or even light green with yellowish tones. Very dark green foliage indicates the plant may need more light. Orchids benefit from being moved outdoors for the summer, but introduce them to outdoor light gradually so that the leaves don’t develop sunburn. Avoid placing the plant in direct sunlight. Bright dappled light works best.
- Humidity — Orchids prefer humid, moist air. The air in most homes during the winter months is too dry and needs to be raised to 50% or more, depending on the orchid species you’re growing. A humidifier placed near the orchid is a good way to increase moisture in the air. Alternatively, place the orchid pot on pebbles in a tray. Add water until it nearly covers the pebbles but doesn’t touch the pot. If you have a collection of orchids, group them together to help hold the moisture in the air. Mist plants only if the humidity is very low. Water sitting on the foliage may invite disease.
- Water — Improper watering is one of the main reasons many orchids do not thrive. It’s important not to let the roots dry out but it’s more important not to overwater. The proper method is to water thoroughly with room temperature water BUT let all the water drain out. Frequency of watering depends on the potting mix and the type of orchid you’re growing but, in general, watering once per week should be sufficient. Avoid watering your orchids with water that has been softened with salt.
- Temperature – Orchids generally like the same temperatures as humans. However, they do not like air conditioning nor do they like temperatures above 95°F. Their maximum comfort level is around the mid-80s. As for minimum temperatures, warm-growing orchids can tolerate minimum nighttime temperatures of about 55 to 60°F. Intermediate-growing orchids can tolerate minimum nighttime temperatures of about 45 to 55°F. Cool-growing orchids can tolerate minimum winter night-time temperatures of around 32 to 45°F. Orchids thrive best if there’s a 15 to 20 degree difference between day and night temperatures.
- Growing Medium — In choosing a growing medium for an orchid, it’s important to mimic the growing conditions in nature. For example, epiphytic and lithophytic orchid roots require access to air. A medium to coarse-grain bark mix is the best choice for these orchid types. Orchids that require more consistent moisture, such as Miltonias and Paphiopedilums, thrive best in a fine-grain bark mix. Sphagnum moss is also used as a growing medium for orchids. However, it may look and feel dry on the surface but can be wet deeper inside the pot. Therefore, it’s more difficult to judge whether the plant needs water. If in doubt, re-pot the plant in a bark mix. Never use traditional potting soil for tropical orchids.
- Fertilization — When orchids are actively growing, fertilize each time you water using water-soluble fertilizer diluted at ¼ to ½ strength. Flush the roots with fresh water monthly to remove fertilizer salts that accumulate in the pot. Any balanced fertilizer may be used, but a 15-15-15 fertilizer with calcium and magnesium works best. Before applying a fertilizer solution, wet the potting medium with plain water first.
HOW TO PROLONG ORCHID BLOOM TIME
When buying an orchid, select one with lots of buds rather than open blossoms. Then, to prolong bloom time:
- Don’t allow the plant to dry out. Orchid flowers need to stay hydrated. Just don’t overwater the plant.
- Do not mist the flowers. Too much moisture on the flowers can lead to disease.
- Make sure air can circulate freely around the flowers.
- Give the flowering plant indirect light according to its needs but don’t place it in direct sunlight.
- Keep the room temperature on the cool side.
- Keep pollinator insects away from the orchid. Once a flower is pollinated, it begins to die.
WHAT TO DO IF YOUR ORCHID FAILS TO BLOOM
Insufficient light is the primary reason orchids fail to flower. Place the plant in an east- or south-facing window with diffused light but no direct sun. In summer, place the plant outside in a spot where it may receive a little early morning or late afternoon sun but will otherwise be in the shade.
Keep the nighttime temperatures cooler than daytime temperatures for bud set.
Check the growing instructions to see if your orchid requires a period of dryness in other to trigger bloom. Some species naturally experience a dormant (dry) season before they will set buds.
HOW TO GET AN ORCHID TO RE-BLOOM
Of the commonly grown orchid species, only the Phalaenopsis orchid will re-bloom from the old flower spike. After the plant finishes blooming, cut the flower spike back to the second or third node on the spike. A new flower spike will eventually develop from one of the nodes, usually within two to three months.
HOW TO DETERMINE WHEN AN ORCHID NEEDS TO BE REPOTTED
Most orchids should be repotted every two or three years to ensure proper aeration and drainage. The frequency of repotting may vary depending on the type of pot, the frequency with which the plants are watered, and the growing medium used. If you’re not sure whether to repot, inspect the bark mix to see if the individual particles have decreased in size, smell musty, or look moldy. As bark mixes degrade, the particles break down, becoming smaller and impeding drainage. At this point, poor drainage can cause the orchid roots to rot. Repot before this happens or if the orchid is unstable from growing out of the pot.
ORCHID PESTS AND PROBLEMS
Common insect pests of orchids include mealybugs, spider mites, scales and aphids. Most pests can be gently dislodged using cotton swabs and rubbing alcohol, particularly mealybugs and scale.
Fungal diseases are the cause of many orchid deaths. To prevent a fungal disease, do not over water the plant or allow water to stand around the roots or collect in the spaces between the leaves. Keep air circulating around the roots. Change the growing medium before it decays. If you detect a fungus, repot the plant as soon as possible.
Orchids are a joy to own. Despite the perception that they are difficult to grow, they actually aren’t. They simply require different care from what you ordinarily give houseplants. Pay attention to their special cultural requirements and they will reward you with weeks or months of exotic blooms.
A happy orchid is one that has:
- New leaves that are larger than the older ones
- A vigorous root system
- Green or red root tips
- Thick, turgid leaves
- Multiple bloom spikes
- No diseases or pests.
CHAOS-Charlottesville Orchid Society (cvilleorchidsociety).
Clemson.edu website Publication GHIC 1560, “Orchids” (clemson.edu/extension/hgic1560/orchids)
American Orchid Society (www.aos.org)
The Practical Encyclopedia of Orchids (Rittershausen, Brian & Wilma, 2014)
“Growing Orchids in the Home,” The University of Tennessee Agricultural Extension Service Publication PB1634 (extension.tennessee.edu/PB1634)
“Flower Power,” by Chuck Woods, University of Florida Office of Research Publications (research.ufl.edu/publications/flowerpower.pdf)