For indoor lilies, such as the popular Peace Lily (Spathiphyllum) or the fragrant Oriental and Asiatic hybrids, maintaining a consistent and appropriate temperature is fundamental to their physiological processes. The ideal temperature range for most indoor lilies is between 65°F (18°C) and 75°F (24°C) during the daytime. Within this range, the plant's enzymes function efficiently, facilitating crucial activities like photosynthesis, respiration, and nutrient uptake. This promotes healthy leaf development, strong stem growth, and, most importantly, the initiation and sustenance of flowering. Temperatures towards the cooler end of this spectrum often encourage longer-lasting blooms.
While daytime warmth is essential, lilies benefit significantly from a natural and slight drop in temperature during the night. A nighttime temperature that is approximately 10°F (5-6°C) cooler than the daytime temperature, ideally around 55°F (13°C) to 65°F (18°C), is highly advantageous. This diurnal temperature variation mimics the plant's natural environment and is a key signal for many biological functions. It allows the plant to slow its respiration rate, conserving energy and sugars that were produced during the day through photosynthesis. This conservation of energy directly translates to more robust growth and more prolific flowering over time.
Drafts, whether cold from a frequently opened door or window in winter, or hot from an air conditioning vent in summer, are extremely detrimental. From the plant's perspective, a sudden blast of cold air is a severe stressor. It can cause rapid chilling injury to plant cells, leading to cellular damage that manifests as browning leaf tips, yellowing leaves, and dropped flower buds. Conversely, a hot, dry draft acts like a desert wind, drastically accelerating transpiration (water loss through the leaves). The roots cannot uptake water fast enough to compensate, leading to wilting, leaf scorch, and overall dehydration. Both scenarios force the plant into a defensive state, halting growth and flowering to conserve resources.
Sustained temperatures above 85°F (29°C) induce heat stress, which disrupts the plant's basic metabolic functions. High heat can denature proteins and damage photosynthetic machinery within the leaves, specifically the photosystem II complex. The plant will respond by closing its stomata to reduce water loss; however, this also simultaneously shuts down the intake of carbon dioxide needed for photosynthesis. Growth stalls, flower buds may abort or fail to form, and the plant becomes susceptible to pests like spider mites that thrive in hot, dry conditions. Providing good air circulation (without a direct draft), increasing humidity around the plant via a pebble tray or humidifier, and relocating it to a cooler room are essential countermeasures.
