Calla Lilies (Zantedeschia spp.) are not true lilies but rhizomatous plants with specific thermic preferences that vary slightly depending on their growth cycle. For active growth and, most importantly, for the initiation and development of their iconic spathes (the colorful flower bracts), they thrive in daytime temperatures between 65°F and 75°F (18°C and 24°C). This moderate warmth supports robust photosynthesis and healthy cellular function without causing excessive stress. Nighttime temperatures should ideally be cooler, dropping to around 55°F to 60°F (13°C to 16°C). This day-night temperature differential is crucial as it mimics their natural environment and helps to prolong the life of the flowers while strengthening the plant's overall structure.
Originating from marshlands in South Africa, Calla Lilies are accustomed to environments with relatively high atmospheric moisture. For indoor cultivation, maintaining a moderate to high humidity level, ideally between 50% and 60%, is paramount. This range supports vital physiological processes, most significantly transpiration and nutrient uptake. Humidity that is too low (common in air-conditioned or heated homes) leads to excessive moisture loss through the leaves, resulting in stressed plants that exhibit symptoms like brown, crispy leaf tips, drooping, and bud blast (where flower buds fail to open and instead dry out and die).
Deviating from the ideal temperature and humidity parameters has direct and observable negative effects on the plant. Consistently high temperatures above 80°F (27°C), especially when coupled with low humidity, will force the plant into a state of heat stress. This accelerates metabolism, leading to leggy, weak growth and significantly shortening the vase life of any flowers that do manage to bloom. Conversely, prolonged exposure to temperatures below 50°F (10°C) can chill the plant, causing growth to stall entirely and potentially leading to root rot as water absorption ceases. Low humidity exacerbates all temperature-related stress, while excessively high humidity (consistently above 70%) in poor air circulation conditions creates a perfect environment for fungal diseases like botrytis (gray mold) to attack the flowers and foliage.
Maintaining these conditions indoors requires attentive care. To increase humidity around the plant, employ a room humidifier, place the pot on a pebble tray filled with water (ensuring the pot's base is not sitting in water), or group it with other plants to create a beneficial microclimate. Misting can provide temporary relief but is often insufficient and can promote leaf fungal spots if done excessively, especially in cool, stagnant air. To manage temperature, keep the plant away from direct heat sources like radiators, air conditioning vents, and drafty windows. During the plant's mandatory dormant period after flowering, temperature requirements change drastically; the rhizome should be stored in a cool, dark place at around 50°F (10°C) for two to three months with very little water to allow for proper rest.
