From a plant's perspective, the ideal temperature range is not a matter of preference but one of physiological necessity. Cyclamen, specifically the popular florist cyclamen (Cyclamen persicum), are geophytes native to the Mediterranean basin and parts of southwestern Asia. Their entire growth cycle is evolutionarily synchronized with the cool, moist winters and hot, dry summers of that region. Their metabolism is optimized for cool conditions. Enzymatic processes that govern nutrient uptake, photosynthesis, and respiration function most efficiently within a specific, cool range. Temperatures outside this range disrupt these processes, leading to stress, reduced energy production, and ultimately, a decline in health and flowering.
The ideal temperature range for a thriving cyclamen is between 60°F (15°C) and 68°F (20°C) during the day. This range provides the sufficient warmth required for active photosynthesis, where the plant converts light into the chemical energy needed for growth and flower production. However, a crucial and often overlooked aspect is the nocturnal temperature drop. At night, cyclamen require a consistent drop to between 50°F (10°C) and 55°F (13°C). This diurnal fluctuation is a critical environmental signal. The cooler nights slow respiration, conserving the energy produced during the day. More importantly, this cool period is essential for the development of strong flower stems and vibrant blooms, preventing them from becoming weak, elongated, and prone to flopping.
When ambient temperatures consistently exceed 68°F (20°C), the cyclamen plant begins to experience significant stress. Its respiration rate increases dramatically, often outpacing photosynthesis. This means the plant burns through its energy reserves faster than it can create them, leading to a net energy loss. The plant's response is a survival mechanism: it will initiate dormancy. Signs of this heat stress include rapid yellowing of leaves, drooping flower stalks, a complete halt in bud formation, and premature flower drop. The plant is essentially aborting its energy-intensive growth and reproductive phases to conserve resources for its tuber, hoping to survive until cooler conditions return.
While cyclamen are cool-weather plants, they are not frost-hardy. Prolonged exposure to temperatures below 50°F (10°C), and especially below 40°F (4°C), causes cellular damage. Water within the plant's cells can freeze, forming ice crystals that rupture cell membranes, leading to blackened, mushy foliage and collapsed flowers. This damage is often irreversible and provides an entry point for fungal and bacterial pathogens. Chilling injury can also occur without freezing, manifesting as stunted growth and leaf discoloration. The plant's metabolic processes slow to a near halt, preventing growth and flowering.
Temperature is intrinsically linked to humidity and transpiration. In the warm, dry air typical of heated indoor environments, the rate of water loss from the leaves (transpiration) increases substantially. This forces the plant to draw more water from its tuber and roots. If the growing medium is also warm, it can exacerbate root stress. Conversely, in very cold, wet soil, root function is impaired, and the plant cannot uptake water effectively, leading to wilting even though the soil is moist. Therefore, maintaining the ideal cool air and soil temperature is fundamental to maintaining a healthy water balance and preventing root rot or desiccation.
