Orchid species have colonlised almost every geographical region although the majority are endemic to the tropical and subtropical regions. From the cultivation standpoint, orchids are conveniently categorised as either being warm, intermediate, cool or hardy growers.
It is a common misconception that all orchids from the tropics require hot temperatures this is because many such species grow at high altitudes and so paradoxically are cool growing. For example members of the genera Masdevallia and Odontoglossum which emanate from tropical South America are to be found in mountainous terrain and resent been grown in warm conditions.
It is also a generalisation to assume that cool-growers must be easier to grow than warmer growing types. This is because some cool-growers may have other more exacting cultivation demands. An example is the South African genus Disa which though very cool growing must have its roots kept constantly in fresh water and will also not tolerate high levels of mineral salts.
Warm Growing Orchids
Warm growing orchids originate from the tropics growing close to sea level. They thrive only when night temperatures are kept between 14° and 16°C with a daytime rise of about 10°C. This temperature regime can often be met in centrally heated homes. The most popular and easy to grow of orchid house plants are the Phalaenopsis and Vanda hybrids and these are warm growers. So warm growing does not always equate to difficult growing.
Intermediate Growing Orchids
Intermediate growing orchids are usually to be found growing at higher altitudes in tropical countries or may be from cooler sub-tropical countries where the night temperatures approximate 12° to 14°C with a daytime rise of about 10°C. An enormous range of orchids can be grown within this temperature zone, many of which are suited to growing in the home, greenhouse or conservatory.
Cool Growing Orchids
Cool growing orchids from tropical climates are usually to be found at moderate to high altitudes. They prefer night temperatures of between 10° and 12°C with a daytime rise of about 10°C. Many can tolerate short periodic temperature drops (down to 7°C) if their growing media is kept drier. More challenging is to keep them healthy during warm summers, particularly if cultivated under glass. Temperatures above 25°C will stress the plants unless there is good air movement. Cool growing orchids are favourites for beginners and there is a spectacular range of genera to indulge in. Perhaps the most beautiful orchids are cool-growing so It is not true that the warmer the growing an orchid is, the more beautiful it has to be.
Hardy orchids are those which are from temperate climates such as here in Ireland and these will tolerate at least moderate frosts. Generally they do not grow well under glass or in the home and are best left outside during the summer and in a sheltered place during the winter (never indoors except perhaps in an unheated greenhouse).There has been a surge in interest in hardy orchids in recent years. These are plants everyone can grow. However do not presume they are all easy, some are notoriously fastidious about their growing environment particularly with regards to drainage for example the genus Cypripedium.
It's worth investing in a Maximum minimum thermometer (as seen above). It will show you the range of temperatures your orchid is in and will help you provide the best environment.