It is hard to know what to do with your orchids for example when to feed and when to water what to spray with etc., as every one and every book has a different way. After 40 years of experience I feel I can give the amateur and expert some guidelines to help you understand a little better about your plants and in turn you should be able to make better decisions when, how and what to do what you have to.
One of the most important things is to remember that nearly all popular cultivated orchids are epiphytes, that means they live on the air and only attach themselves to a host for support. The host takes the form of trees or rocks etc., and with the use of leached out salts from these droplets that are mixed with rainwater or droplets of mist to form food that splashes on the leaves and roots. The leaves and roots absorb most of the moisture, during rain or when the humidity is at it's highest. Orchids that are generally cultivated are found predominantly in a wide variety of conditions ie., forests and all of these forests have one thing in common like the rest of the places that orchids grow. The humidity increases during the night and is much lower in the day, but this can vary when it's raining. Where orchids are plentiful in their natural habitat a light to heavy mist or fog can be readily seen almost every night.
Most orchids have adapted to use this higher night humidity to absorb moisture through their leaves and root. Where plants have extended drought or dry seasons, species such as Dendrobium bigibbum, Dendrobium canaliculatum and Dendrobium bifalce regularly endure then they rely on this night rise of humidity to survive for many months. Often if a wet season is missed they can last for up to two years as has just happened in Papua New Guinea. Almena or as in Pidgin English the Big Sun.
How do plants maintain the moisture without loosing it during the day?
If you look closely at an orchid leaf or new root you will see lots of small dents, which are holes, called stomata. These holes open as the sunlight dwindles to darkness or as the light is greatly reduced because of heavy cloud and as the sunlight becomes brighter they close so reversing the process. Commonly known as Stomatal Rhythm.
This process helps the plant hold moisture within itself when in strong light and replenish what moisture is lost at night.
It is this reversal of the normal Stomatal Rhythm, which enables Crassulacean Acid Metabolism (CAM), in orchid plants to be drought tolerant. CO2 diffuses into the leaves and is fixed into organic acids during the night, when temperatures are low and humidity is high, so minimising the loss of water by transpiration (Arditti and Sinclair).
What does this mean?
Only use insecticides or fungicides that are not oil based such as white oil as the will seal over the stomata. Use an agricultural wetting agent to help spray cover the leaves and roots that reduces the meniscuses on the water. If none is available use a little dishwashing detergent but only use a few drops and mix well in.
Not many plants CAM and Orchids are one of the few groups of plants that do another group is Succulents.
Orchid roots can tell you a lot if you have a little understanding of them also. Keeping in mind and applying the above information the roots will tell you if they like being potted in a fine, coarse mix or even mounted on a wet or dry host just hanging free in the air.
If the new root ends are white they can be potted in a medium that is not very open, but if the ends are green there is a need for a fresh supply of oxygen and the darker the green those tips are the more open the mix should be.
For example Phalaenopsis and Vanda plants have a few roots that secures the plant to the tree and all the rest hang in the moist air these root tips are dark green and the roots are thick.
Spathoglottis have thin roots and like a close medium.
Dendrobiums have white green root tips that are medium thickness and nearly all species have dark green root tips. They do best on a host but will do fairly in a pot that has plenty of holes in to let in the air along with an open potting mix that does not become soggy but maintain a small amount of moisture.
Just remember research your orchids and where they come from, or what species are in your hybrids this will give you the information on what your orchids require as to building a microclimate and to assist you in growing better orchids.