The Orchidaceae family is one of the largest and most diverse plant groups, containing tens of thousands of species native to nearly every habitat except glaciers. This vast geographical spread means there is no single answer to whether orchids tolerate or “like” cold weather. The relationship between an orchid and cool temperatures is complex, ranging from necessary for survival to a biological trigger for reproduction. Understanding a specific plant’s thermal requirements is primary to successful cultivation and determining its health and ability to bloom.
Understanding Orchid Temperature Categories
Orchids are broadly classified into three categories based on the temperatures of their native environments. This classification dictates their overall survival range for healthy growth and is the primary way growers determine if a species is suited to a warmer or cooler climate.
Warm-growing orchids originate from tropical lowlands and are the most sensitive to cold, preferring consistently high temperatures. These species, which include the common Phalaenopsis (Moth Orchid), thrive with daytime temperatures between 75°F and 85°F and nighttime temperatures between 65°F and 75°F. Prolonged exposure below 60°F can induce significant stress in these varieties.
Intermediate-growing orchids are the most adaptable group, thriving in conditions that mimic moderate subtropical or higher-altitude tropical zones. Plants in this category, such as many Cattleya hybrids, prefer daytime temperatures between 70°F and 80°F, with nighttime lows between 55°F and 65°F. This range is often the easiest to maintain in a typical home environment, making these orchids popular choices for houseplant enthusiasts.
Cool-growing orchids are adapted to high-elevation cloud forests or temperate zones and require cooler conditions for proper growth. Genera like Odontoglossum and some Masdevallia species prefer daytime temperatures between 60°F and 70°F. Their metabolism is optimized for nighttime temperatures that consistently dip to the 50°F to 55°F range, and they struggle when exposed to prolonged heat.
How Cool Temperatures Trigger Flowering
Beyond general survival, a controlled period of cooler temperatures is a biological requirement for many orchids to shift from vegetative growth to flowering. This process is distinct from the general temperature ranges required for everyday health.
The most common flowering trigger is the diurnal temperature swing, which is the difference between day and night temperatures. Most orchids benefit from a temperature drop of 10°F to 15°F between the peak daytime temperature and the overnight low. This drop signals the plant that seasonal conditions are changing, prompting the initiation of a flower spike.
Cooler night temperatures are metabolically important because they allow the plant to conserve energy. During the day, the orchid produces sugars through photosynthesis, but at night, it consumes those reserves through respiration. Since the rate of respiration is temperature-dependent, a cooler night slows this consumption. This allows the plant to store the excess energy needed to support the demanding process of producing a flower spike.
Many popular orchids, including Phalaenopsis, require a specific cooling period, often two to three weeks, with nighttime temperatures in the 55°F to 65°F range to initiate blooming. Without this signal, the plant will only produce leaves and roots, which is why otherwise healthy orchids become “shy” bloomers. Genera like Cymbidium and certain Dendrobium species are dependent on this seasonal cooling for successful flower bud development.
Recognizing and Preventing Cold Damage
While a cool period can be beneficial for flowering, temperatures below a species’ minimum survival threshold will cause cold damage. This damage manifests in two forms: chilling injury or frost damage. The severity of the injury depends on the duration and depth of the temperature drop.
Chilling injury occurs when the temperature is above freezing, typically below 50°F for warm-growing varieties, but low enough to disrupt cell membranes. Symptoms are not immediately visible but appear days later as water-soaked spots on leaves, which turn black or brown as the tissue collapses. Severe chilling can also cause bud blast, where flower buds suddenly turn yellow and drop off.
Frost damage is more immediate and severe, occurring when temperatures drop to or below 32°F and water inside the plant cells freezes. The ice crystals rupture the cell walls, leading to a limp, translucent appearance followed by blackened, necrotic tissue that looks like a burn. Pseudobulbs may become squishy and brown, indicating permanent structural damage.
Preventative measures focus on insulation and careful water management leading into a cold period. It is recommended to avoid watering plants before a predicted cold snap, as drier potting media and less moisture in the plant’s tissues can increase cold tolerance.
Indoors, plants should be moved away from uninsulated windows or exterior doors prone to cold drafts. For orchids kept outdoors, covering them with a frost cloth or moving them to a sheltered location, like a porch or garage, can provide the necessary protection. If cold damage occurs, the affected tissue should be removed, and the plant should be kept in a humid, shaded environment until new growth appears.