The Kalanchoe blossfeldiana, often sold as a flowering houseplant, is a popular succulent cherished for its thick, fleshy leaves and vibrant, long-lasting flower clusters. While resilient and drought tolerant, their growth and ability to bloom depend entirely on receiving the correct light exposure. Light dictates everything from vegetative growth to the formation of flower buds. Understanding the precise light requirements ensures this succulent thrives and reblooms indoors.
Optimal Light Requirements for Growth
Kalanchoe plants perform best in bright, indirect light for general vegetative growth. The plant should receive strong illumination throughout the day, but the sun’s rays must be filtered or diffused. The ideal duration for healthy photosynthesis and robust foliage development is approximately six to eight hours of bright light daily.
Indoors, an east-facing window is often the best location, providing gentle, direct morning sun followed by bright, indirect light for the rest of the day. South or west-facing windows offer the strongest light, but the intense, direct afternoon sun can easily scorch the leaves, especially during summer months. If using a south or west exposure, diffuse the light by placing the plant a few feet away from the glass or using a sheer curtain. Prolonged exposure to intense, direct midday sunlight will cause harm.
Supplemental light can be used to achieve the necessary intensity, particularly when natural light is low. A full-spectrum grow light can be positioned 12 to 20 inches above the plant and run for 12 to 16 hours daily to encourage vigorous growth. High light levels during the vegetative phase lead to a bushier, stronger plant structure with the energy reserves needed to support abundant flowering.
Light Adjustments to Induce Blooming
Kalanchoe is classified as a “short-day” plant, meaning its flowering is triggered by the length of the continuous, uninterrupted dark period. This biological response mimics the shorter days and longer nights of late autumn and winter. To successfully force a Kalanchoe to bloom indoors, the grower must artificially create these conditions for a sustained period.
The plant requires a minimum of 12 to 14 hours of absolute, continuous darkness every 24 hours to initiate flower buds. This strict dark period must be maintained for approximately six to eight weeks for complete floral induction. Even a brief flash of artificial light during the dark cycle can disrupt the process and prevent bud formation.
To achieve this photoperiodic control, the plant must be moved into a completely dark space, such as a closet, an opaque box, or a covered area, for the specified duration each evening. The plant can then be returned to its bright, indirect light location for the remaining 10 to 12 hours of the day to allow for photosynthesis. Once the six to eight week period is complete and small flower buds become visible, the plant can be returned to its normal bright light conditions to encourage the buds to develop and open.
Recognizing Symptoms of Improper Light
The Kalanchoe communicates light stress through distinct physical changes in its foliage and structure. Recognizing these symptoms allows for immediate adjustment of the plant’s placement.
Too Little Light
Insufficient light results in a condition called etiolation, where the plant appears stretched or “leggy” as it desperately reaches for a light source. The stems will become noticeably elongated and weak, with large distances between the sets of leaves. The foliage may also appear pale green or yellow due to reduced chlorophyll production, indicating a lack of energy. A plant suffering from low light will also fail to bloom, as it lacks the energy reserves and the photoperiodic trigger necessary for flower formation. If these symptoms appear, the plant must be relocated to a brighter spot, such as an east-facing window, or supplemented with a grow light.
Too Much Light
Conversely, exposure to excessive or overly intense direct sunlight causes visible damage to the succulent leaves. Symptoms of too much light include leaf scorch, which appears as brown, black, or dry, crispy patches on the foliage. The leaves may also develop a reddish or yellow discoloration, which is the plant’s defense mechanism against high light intensity. In severe cases, the entire plant can appear stunted, as it focuses energy on survival rather than growth. If scorching is observed, the plant should be immediately moved away from the direct source, such as behind a sheer curtain or to a slightly less exposed window, to allow the leaves to recover.