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 There are several "rules of thumb" that can be followed for growing most individual genera of orchids. It would be somewhat presumptuous to attempt to give a comprehensive overview of how to grow orchids here. There are already volumes written on how to grow many genera and even individual species.
There are however, several things that the novice grower may want to know in order to make some choices about what kind of orchids to try first, based on their growing environment. Even experienced orchid growers may want to venture out and try something different from time to time.
All orchids are dependent upon water, growing medium (or at least support), light, nutrients, and air circulation. Different genera and species have specific requirements and different levels of tolerance for all four of those things. If you have a greenhouse, a sun room, or live in a warm region, you will find it possible to adjust your growing area to meet the needs of a wide variety of orchids. If, on the other hand, you live in a terribly cold area such as ours, or an apartment building , you may find it more complicated to provide the same conditions - but you may find meeting that challenge very rewarding.
Light
Very few orchids tolerate full direct sun. Even those that do, usually get a reprieve from the sun at midday from other vegetation. There are a few exceptions. Even those that are sun tolerant in their native habitat, may turn black and die quickly if you grow them inside all winter, and then take them out of your home, apartment, or greenhouse in Summer and expose them suddenly to too much sun. Also keep in mind that window glass filters out a lot of ultraviolet rays, but a plant sitting very close to a window can get extremely hot on even mild days. You can burn the leaves of even the toughest Cattleyas and Oncidiums on a windowsill, in June, almost anywhere in the continental United States. No - Orchids are not sensitive, picky, or temperamental for the most part. You can't grow African violets or much of anything pressed against a south facing window year 'round - without at least rendering them terribly damaged and unattractive. Many orchids that are grown in homes or even greenhouses will love it if you take them outside during the summer. Many of them enjoy being suspended under trees, but remember that you have to be sure they are not getting too much or too little sun. Although it may sound unlikely, it is also possible to starve some orchids of light if you live on a heavily wooded site, with very dense trees. Most orchids do well if they get direct sun only in early morning and in late afternoon. There are a few that are true shade lovers, and a few that love to "sunbathe". There are many sources which list specific light requirements for individual plants.
Water
Most orchids are fairly tolerant of tap water, but will perform much better if you use rain water. There are some exceptions here as well. Phragmipediums in general prefer much purer water, and are very sensitive to mineral salts. Using reverse osmosis filtered water may be necessary if you live in an area that has too much copper, or even too much calcium in it. High levels of calcium in your water may not seriously harm your Cattleyas, Vandas, Oncidiums, or your Phalaenopsis to mention a few, but it may leave white deposits on their leaves which are very unattractive . If you have truly exceptional levels of calcium in your water, over time it can actually build up deposits that are heavy enough to block out light from the leaf surfaces. If you use tap water, be sure it is not terribly cold when you water your plants. Very cold water will shock plants and in some cases will do root damage. If you let tap water sit in a container for several hours, near the plant, or in some place that has a similar temperature, it will warm up enough to use it, and it will also allow the chlorine to escape. Never water your orchids outdoors with a garden hose that has been lying in the sun for hours, without first running water through it and emptying the hot water inside, as you can scald them.
Nutrients
In nature, orchids receive their nutrients in a number of ways, some simple, and some quite complex. Different genera and species may have quite different nutrient requirements, or even very different levels of tolerance for nutrients. Water soluble fertilizers are most commonly used, but some orchids, such as Cymbidiums can be fertilized with slow release fertilizers. The growth habits of orchids - particularly whether they are epiphytic, saprophytic, or terrestrial, will affect the kind and amounts of nutrients/fertilizer you should use. Orchids can be dipped, sprayed, or watered with fertilizers in many cases, with little difference in the outcomes, depending on what type of fertilizer you use. some orchids exhibit a "dormant" period or at least a period that they receive little water and no fertilizer.
Air Circulation
Most orchids benefit a great deal from good air circulation. This is often neglected. One must keep in mind that good air circulation in a greenhouse or a home, is not the same as a "draft" or the blast from a central air conditioning or heating duct. Keeping a Phalaenopsis too close to an outside door that gets a lot of traffic, a heating or cooling duct, or near an open window on a cool night, could well result in "blasting" the buds. Running exhaust fans in a greenhouse too long, on very cool nights, can do the same thing. Cool damp conditions also can increase the growth of harmful fungi such as fusarium. Neither is it good to merely use fans to blow hot air over your orchids - particularly if it is very dry air. Air movement around your orchids that approximates a "gentle breeze" is probably quite adequate for most of them. If you take them outdoors in summer, you may want to adjust your watering depending on how humid your climate is generally during summer, and how often it rains on them or how often you water them. Also keep in mind that thunderstorms and hail can blow your orchids off benches or out of trees, so if you leave for vacation, you may not only want to be sure someone is watering your orchids, but you also may want to move them temporarily to a place where they are not likely to be blown away or hailed on. If you grow in a greenhouse, remember that during summer months, your greenhouse can reach incredibly high temperatures if it is exposed to lots of sun during a power outage. Many orchids are generally "happy" in their surroundings if you feel comfortable with the ambient temperature and air circulation. At the same time, you need to learn the moisture and temperature requirements of specific plants in your collection, and move them around your home, yard, or greenhouse space, to
accommodate all their needs, including how much air circulation they receive.
Growing Media
Growing media for orchids encompass a wide array of substances including natural products such as bark, tree fern, moss, cork, or even tree limbs. Synthetic materials are constantly being developed, altered and tested, as the availability of organic materials becomes limited, more costly, or growers have trouble with it decomposing to quickly. Some orchids grow better "mounted" on slabs of bark, cork, or tree fern, than in pots. Some growers may succeed with a particular orchid plant in a pot, while others can only grow it as a mounted plant. Potting media are greatly affected by your growing conditions. Fungus gnats can infest potting media and break them down, turning them to "mud" in the bottom of a pot, and rotting roots. Some media require that you alter your watering methods or schedules, depending on how much water they absorb, and how much they retain. Sometimes, you may want to try several different media to see what works best for you.
Pests
Orchids are susceptible to several pests, the worst probably being scale and slugs. Mealybugs can do extensive damage over time, but are fairly easily eradicated. Scales can kill many types of orchids very quickly and spread rapidly to other plants by airborne transmission. Scale is very difficult to eradicate sometimes, and may require frequent treatment with insecticides and very careful removal from all parts of the plant, including crevices and around roots that are hard to clean without damage or without
un-potting the plant. Slugs, snails, and bush snails eat tender growth, buds, blossoms, and root tips. They are difficult to control in many cases. The use of pesticides is often regulated in certain states, or locales. You may be wise to contact a licensed pest management person to treat your plants. Remember that several pesticides are quite harmful or even lethal to humans, dogs, cats, fish, and birds. Never use dangerous pesticides on plants you grow in your home. Aphids, mealy bugs and scale can be removed or even eliminated completely by using cotton swabs dipped in rubbing alcohol. You can look for slugs and snails during the evening when they emerge to feed, and pick them off and toss them into alcohol. Remember that young snails, slugs, and even mature bush snails are really tiny and you may even need to use tweezers to pick them off the plant or out of the growth medium.
There are many books and other sources available that give much more detailed information about all the topics mentioned above. I strongly encourage everyone to visit The
American Orchid Society website where you can find specific information about temperatures, light requirements, nutrients and all aspects of growing almost all cultivated orchids.
Happy Orchid Growing!
RLK
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