New Guinea orchids are on average neither more difficult nor easier to please in cultivation than those from other regions. Their requirements are however far from uniform so it is difficult to give general guidelines. Some parts of New Guinea experience a true dry season, and this should be reflected in the cultivation of species originating from such areas. However, for most of New Guinea it can be stated that there just is a wet season and a wetter season. Long droughts are exceptional and when they occur many orchids are killed. In most areas the yearly rainfall is about 4000 mm and may exceed 8000 mm locally. The first figure corresponds to about 11 litres of water per square meter per day. That is a lot of water. This does not imply that the average New Guinea orchid should be imagined as growing in a swamp. Even in the wettest areas, such as the upper montane cloud forests, it will not usually rain twenty-four hours a day, and few days will pass without any sunshine at all. Epiphytic orchids in the lowlands and those growing high up in the trees in the mountains frequently have to cope with several hours and on occasion several days of desiccation. Yet others grow in the protective fur of living mosses that envelopes the trees especially at high altitudes, and these orchids can be very intolerant of drought. For terrestrial orchids it is even more difficult to state general rules, as here not only altitude and exposure, but also soil type and drainage are factors to be taken into account. A gross simplification is to divide the terrestrials into forest plants, requiring shade and a humus-rich soil, and grassland plants, requiring sunshine and often a more mineral soil.
Even closely related species can vary greatly in their response to the conditions in cultivation. Mediocalcar decoratum (deco1529.JPG) grows like a weed in any cool humid greenhouse, but M. geniculatum (OR18-036.JPG) increases very slowly and rarely thrives away from its native mossy forest. Dendrobium forbesii (OR14-063.JPG) is easy to grow, the fairly similar looking D. engae (OR14-058.JPG) is quite a tricky plant. Most species of Pedilochilus are difficult to grow for no apparent reason.
Sometimes it is fairly obvious why certain species fail to survive in cultivation. This is true for the leafless terrestrials that are often called 'saprophytes'. If they really were saprophytes, that is, organisms capable of decomposing organic matter, then they would perhaps be easy to cultivate in a big pile of leaf litter. In fact such orchids are parasites on fungi, which is quite a different situation. Difficult to grow, even to keep alive, are also the subalpine orchids, comprising roughly those species occurring above 3000 m altitude. They require a combination of low temperatures, high light intensity, lots of moisture, and plenty of fresh air, which is very hard to realise in a normal greenhouse. It is a great pity that some of the most attractive New Guinea orchids belong to this category, such as Dendrobium brevicaule (OR18-007.JPG), D. dekockii (OR18-005.JPG) and D. vannouhuysii (OR24-101.JPG).
To leave potential cultivators not entirely in the dark we have attempted to assign each species in the checklist to a category which gives at least a clue to its cultivation. Some species could well have been admitted into more than one category, but in such cases only one has been chosen. To give just a single example, the lovely Dendrobium cuthbertsonii (OR14-093.JPG ; for many growers their favourite New Guinea orchid) is usually found as an epiphyte in montane forest but may also occur in open turf and on steep road banks. In the checklist it is only listed as a cool growing epiphyte.
Warm growing means: day temperatures between 25 and 30 °C and night temperatures between 18 and 20 °C; intermediate growing means: day temperatures between 22 and 27 °C and night temperatures between 15 and 18 °C; cool growing means: day temperatures between 16 and 21 °C and night temperatures between 7 and 13 °C.
Alternatively, these indications can roughly be translated into altitudinal ranges:
warm - below 500 m above sea level (asl.).
intermediate - 500 to 1800 m asl.
cool - above 1800 m asl.
A final note of warning: when a species is said to require cool conditions and high light intensities it will definitely need some shading in cultivation when the temperatures can not be prevented from reaching 23 °C or more!