The temperature at which an orchid is maintained is a primary factor influencing its health, growth, and ability to flower. While most orchids originate in tropical and subtropical regions, their natural habitats span vast elevations, from sea level jungles to mountain cloud forests. This diversity means there is no single ideal temperature for the entire family of plants; rather, temperature requirements are highly specific to the orchid’s genus and natural environment. Understanding these specific thermal needs is fundamental to successful orchid cultivation.
Grouping Orchids by Temperature Needs
Horticulturalists classify orchids into three main temperature groups: warm, intermediate, and cool-growing, based on the minimum night temperatures they require.
Warm-Growing Orchids
Warm-growing orchids, such as Phalaenopsis (Moth Orchid) and Vanda, prefer the highest temperatures, mimicking low-elevation tropical environments. These varieties thrive with daytime temperatures ranging from 75°F to 85°F. Nighttime temperatures should remain warmer, typically between 65°F and 75°F.
Intermediate-Growing Orchids
Intermediate-growing orchids, including Cattleya and Oncidium, require a slightly cooler environment, reflecting their origin at higher elevations. Their ideal daytime range is between 70°F and 80°F. Nighttime temperatures for this group should drop to between 55°F and 65°F, making them often the most adaptable to typical household temperatures.
Cool-Growing Orchids
Cool-growing orchids, including Cymbidium and Masdevallia, come from the highest, cloud-shrouded elevations where temperatures are significantly lower. These plants require the coolest conditions, with daytime temperatures between 60°F and 70°F. The nighttime temperature must consistently fall to between 50°F and 55°F, as this distinct chill is necessary for proper growth and bloom initiation.
The Essential Role of Nighttime Temperature Variation
Beyond maintaining a specific temperature range, the fluctuation between day and night temperatures plays a significant role in orchid physiology, particularly concerning flowering. This diurnal temperature differential is necessary for the plant to properly manage its metabolic processes. During the day, the orchid performs photosynthesis, converting light energy and carbon dioxide into sugars and starches.
At night, photosynthesis ceases, but the plant continues to consume these energy reserves through respiration to support growth and maintenance. Respiration occurs more quickly at higher temperatures, meaning warm nights cause the plant to burn through its stored food faster. Lower nighttime temperatures slow the rate of respiration, allowing the orchid to conserve the carbohydrates it manufactured during the day.
This conservation of energy is necessary for successful flowering, as the stored carbohydrates are used to produce flower spikes and blooms. Most orchids benefit from a temperature differential of 10°F to 15°F between the day and night cycles. Without this cooler period, the plant often fails to initiate flower spikes, a common issue for orchids grown in environments with constant temperatures, such as offices. Even a modest temperature drop is often sufficient to trigger bloom initiation in many popular hybrid varieties.
Avoiding Temperature Stress and Extremes
Temperatures that fall outside an orchid’s preferred range can quickly cause stress and irreversible damage, making it necessary to avoid both excessive heat and cold. Heat stress occurs when temperatures rise too high, typically above 90°F, or when the plant is exposed to prolonged periods of high heat. This excessive heat causes moisture to evaporate from the plant’s tissues faster than the roots can replace it, leading to dehydration.
Symptoms of heat stress include yellowing or withered leaves, which may take on a leathery texture, and shriveled pseudobulbs indicating moisture reserves are depleted. Mitigation involves increasing air movement, such as with a fan, to help cool the plant through increased evaporation, and immediately shielding the orchid from direct, intense sunlight. Placing an orchid near heat sources like vents or fireplaces can also cause localized heat damage, even in winter.
At the opposite extreme, most orchids face a lower danger limit at or below 50°F, which can cause chilling injury. Exposure to temperatures below this threshold can lead to mesophyll cell collapse, which manifests as pitting, discoloration, or water-soaked lesions on the leaves. This damage may not become visible until days after the cold exposure.
To prevent cold damage, growers must ensure orchids are not placed near drafty windows, exterior doors, or in the path of cold air conditioning blasts. The danger is particularly acute when the plant is wet, as cold water on the leaves can accelerate cell damage. If a plant is exposed to a sudden cold snap, it should be moved to a cool, non-heated area and kept dry, as excessive watering can worsen the damage and encourage fungal infection.