The Kalanchoe blossfeldiana, commonly known as Florist Kalanchoe, is a resilient succulent native to Madagascar that has become a widely popular houseplant. Its thick, fleshy leaves and vibrant clusters of flowers make it an attractive and low-maintenance choice for indoor environments. Although it tolerates a range of conditions, temperature is the single most defining factor in its long-term health and ability to produce its characteristic blooms. The ideal temperature range for the Kalanchoe mimics the slightly cooler nights and warm days of its native subtropical habitat.
Optimal Daytime and Nighttime Growing Temperatures
The period of active growth for the Kalanchoe is best sustained when daytime temperatures are consistently kept between 60 and 75 degrees Fahrenheit, or 15 to 24 degrees Celsius. Within this range, the plant can efficiently perform photosynthesis and maintain a healthy, compact structure. Placing the plant near a sunny window without direct exposure to drafts or sudden temperature shifts will help keep conditions stable during the day.
A slight, but noticeable, temperature drop at night is beneficial for healthy Kalanchoe development. The ideal nighttime range is slightly cooler, falling between 50 and 60 degrees Fahrenheit, or 10 to 15 degrees Celsius. This diurnal temperature fluctuation, where the night is cooler than the day, is a natural signal that helps regulate the plant’s metabolism, a trait common among many succulents.
This temperature difference supports the Kalanchoe’s Crassulacean Acid Metabolism (CAM) cycle, a specialized form of photosynthesis where the plant opens its stomata at night to absorb carbon dioxide. The cooler nighttime temperatures reduce the rate of water loss during this gas exchange, allowing the plant to conserve moisture more effectively. Prolonged exposure to temperatures above this optimum, especially at night, can interfere with the plant’s ability to initiate flowering.
Temperature Requirements for Bloom Induction
The Kalanchoe is classified as a short-day plant, meaning it requires specific light and temperature cues to transition from vegetative growth to flowering. This process is triggered by a combination of long periods of uninterrupted darkness and a sustained period of cooler temperatures. Simply reducing the light exposure is often not enough to prompt the plant to set buds without the corresponding drop in temperature.
To successfully induce blooming, a temporary cooling period must be introduced for approximately six to eight weeks. During this time, the plant must be subjected to a strict regimen of 12 to 14 hours of complete darkness every 24 hours. Concurrently, the temperature should be maintained in a specific cooler band, ideally around 45 degrees Fahrenheit at night and 60 degrees Fahrenheit during the day.
Maintaining this cooler thermal environment is necessary because high night temperatures can cause “heat delay,” which prevents or significantly slows down flower initiation. The combined stress of reduced light and intentional cooling signals to the Kalanchoe that winter is approaching, prompting it to shift its energy toward flower production. Once buds begin to form, the plant can be returned to its normal, warmer growing temperatures to support the development and opening of the flowers.
Survival Limits and Danger Zones
While the Kalanchoe is a relatively tough succulent, it is extremely sensitive to cold. The plant begins to show signs of stress and damage when temperatures drop consistently below 50 degrees Fahrenheit (10 degrees Celsius). Exposure to temperatures below 45 degrees Fahrenheit (7 degrees Celsius) can lead to severe physiological damage.
The absolute danger zone for the Kalanchoe is any temperature at or below freezing, which is 32 degrees Fahrenheit (0 degrees Celsius). As a succulent with high water content in its leaves and stems, the plant’s cellular structure is quickly destroyed by frost, which is almost always fatal. Any Kalanchoe kept outdoors must be brought inside well before the first expected frost to prevent this irreversible damage.
Excessive heat also poses a threat to the plant’s health. Sustained high temperatures above 80 degrees Fahrenheit (27 degrees Celsius) will cause the leaves to wilt and stress the plant. If the temperature rises above 90 degrees Fahrenheit (32 degrees Celsius) for an extended period, the plant may enter a state of protective dormancy. Providing protection from intense, midday sun and ensuring good air circulation are practical steps to mitigate the effects of high heat during summer months.