Most people tend to think of hot steamy jungles with oppressive humidity and constant rainfall when they think of orchid habitats. Although this is true for some, a majority of orchids are found elsewhere. Since the earth is not flat there are many different microenvironments all over this planet where orchids thrive. Cloud forests for example. These tropical or subtropical mountain forests, common to South America, are characterized by a persistent cloud cover at canopy level. They are filled with a wide variety of ferns, mosses – and a lot of fantastic orchids. When the sun is out temperatures can rise quite a bit on the mountain, but at night temperatures drops notably the higher the altitude. Ideal for cool growing orchids. Orchids are divided into groups of cool, intermediate, warm and hot growers. Many are quite forgiving about daytime temperature; it is the diurnal temperature variation that is crucial. Diurnal temperature variation is the variation in temperature from the highs of the day to the cool of nights. Providing cooler nights will help reduce the stress of warmer days for those preferring cooler growing conditions overall. Many orchids require a 10-15 degree drop in temperature at night for a minimum of 3-4 weeks to induce flowering. This is because orchids need cooler temperatures in order to store the nutrients it has generated during the photosynthesis, if it is too warm it metabolizes it instead of producing blooms.
Cool growing orchids
10-13 night / 15-21 day
Cool growers are found at relatively high elevations (above 2500 meters). However, this does not mean that it is really cold there all the time. It may get really warm while the sun is out but the temperatures drops considerably at night or on cloudy days, sometimes as much as 15 degrees. So in cultivation you should aim at simulating this diurnal temperature change range more than hitting the exact temperature. Most plants from these regions will also need more humid growing conditions (but not exceedingly wet) as the natural habitats always are covered in a dense fog where the hot humid jungle air meets the cool dry mountain air.
Intermediate growing orchids
13-18 night / 18-24 day
Intermediate growers will be found in elevations of 1800 to 2500 meters and the day to night temperature change is closer to 10 degrees. Days can be fairly hot and the precipitation may also be more seasonal than in the cold climates. This is why some intermediate species require a rest period.
Warm growing orchids
18-21 night / 21-29 day – never lower than 7 degrees
Warm growers come from elevations of 1000-1800 meters. It can be either very constant or seasonal conditions, why certain species need a rest period according to seasonal changes. Rest periods are important in cultivation. Daytime temperatures can get quite warm, up to 32 degrees, but day to night temperature change is still about 8-10 degrees.
Hot growing orchids
21-24 night / 24-32 day – never lower than 10 degrees
Hot growers can be found from sea level to 1000 meters. Generally the day to night temperature change is only about 5-10 degrees on average and warm growers tend to enjoy a more constant watering schedule.
My growing areas
I like to keep my growing room at the intermediate level. But since I grow in an apartment I am limited to how I can control the climate for my orchids. But I keep one of the windows cracked open a little bit almost year around and never turn on the heating element. By closing the door at night I can bring the temperature down quite a bit, then by just opening the door in the morning the temp creeps back up during the day. During the colder months (November-March) the night time temperature drops to about 15 degrees while daytime temps hover around 20-22 degrees. The warmer part of the year the temperatures are a few (3-5) degrees warmer thanks to a fairly shady location and thick brick walls.
I wanted a dedicated space for a few intermediate to warm growers so I converted a terrarium to a small vivarium in my growing room (75x80x40 cm). The ambient temperature in our apartment stays around 20-24, maybe as high as 28 on sporadic days in the summer. With the help of the heat from the light, I am maintaining 20-24 degrees during the day, 15-18 at night most of the year, a few degrees cooler some days in the winter. At night when the light is off the temperature inside drops to about the same level as the growing room. I use synthetic wine corks to make an air space between the light and the glass on top to help lead some of the heat away when needed. In the winer I need all the heat I can get, but in the fall/spring I use 1/2 a cork, and in the summer a whole cork. Very scientific…
For the cool air intake installation I got a simple duct fan (Ventilution 100mm, two speed 145/187 m³, 27/34 dBA) and installed it to pull in air from the old school vent in the orchid room (a square hole in the wall leading to the outside). Some plastic flex tubing bring the cool air to the viv. at the other side of the room. This works well about 9 months out of the year. I use a Bozz ACR6000 portable air conditioner to help cope during the warmer summer months. A Lucky Reptile Thermo Control PRO II thermostat handles the regulating part. I have it set to keep 20 degrees during the day and 10 degrees at night all year except for a few short weeks in the summer when I allow it to go up a couple of degrees more if needed to keep the AC from frosting over too bad.
This is where I raise my baby orchids from flasks, and I heat these with a radiant heat mat, the same used to heat reptile terrariums. That allows me to create a slightly warmer mini micro climate in the intermediate growing room. The temperature in the greenhouses stay around 18-24 degrees.