Indoor succulents often require supplemental lighting because the natural light available inside a home is rarely sufficient to replicate the intense, direct sun they thrive in outdoors. Standard windows filter out significant light intensity, and the duration of effective sunlight exposure is shortened. Providing artificial illumination is necessary to maintain the plant’s characteristic compact shape and vibrant coloration. The amount of time a grow light needs to be on balances the light’s intensity with the plant’s biological requirements.
Understanding Succulent Light Requirements
Succulents are adapted to extremely high levels of light intensity, often referred to as full sun. This intense illumination is necessary to fuel photosynthesis and prevent the plant from stretching out in search of brighter conditions. Light intensity and light duration work together to provide the total amount of light energy a plant receives in a day.
This total energy is measured as the Daily Light Integral (DLI), which is the accumulation of light over a 24-hour period. Since indoor grow lights are typically less intense than natural sunlight, the duration of illumination must be extended to meet the plant’s high DLI needs. A weaker light source must be left on longer to deliver the same amount of energy as a powerful one.
Many succulent varieties utilize Crassulacean Acid Metabolism (CAM), a specialized form of photosynthesis. This process is an adaptation to arid environments, allowing the plant to conserve water by closing its stomata during the hot day. The plant takes in carbon dioxide at night when temperatures are cooler.
The CAM cycle requires a distinct period of darkness to fix the carbon dioxide into organic acids for later use. While the light reactions of photosynthesis occur during the day, the nighttime phase is equally important for the plant’s metabolism. Therefore, the photoperiod must be managed to support both phases of this unique process.
Determining the Ideal Grow Light Duration
The most common time range for providing artificial light to succulents is between 12 and 16 hours per day. This extended period compensates for the lower intensity of artificial grow lights compared to direct outdoor sun. The goal is to provide a consistent daily dose of light energy to encourage compact growth and maintain stress coloration.
The specific number of hours depends on the strength of the light source being used. If you are using a high-intensity LED fixture designed for growing plants, 12 hours may be sufficient for many common succulents. If the light source is a less powerful standard LED or fluorescent bulb, the duration should be increased toward the 16-hour maximum to ensure adequate energy delivery.
A few varieties that prefer slightly lower light, such as Haworthia or Gasteria species, may thrive with a 10-to-12-hour schedule. However, most rosetted succulents like Echeveria or Sedum often require 14 to 16 hours to prevent stretching. It is not recommended to exceed 16 hours, as this disrupts the plant’s natural light-dark cycle.
The dark period is just as important as the light period. The plant needs a minimum of eight hours of uninterrupted darkness to properly execute the CO2-fixing phase of CAM photosynthesis. Without this consistent dark period, the plant cannot effectively take in the carbon dioxide required for growth, which prevents metabolic dysfunction.
Setting Up and Monitoring Your Lights
To ensure effective light duration, the light source must be positioned correctly over the plant canopy. Lower-power fluorescent tubes typically need to be placed close, often within 6 to 12 inches of the succulent top. Modern, powerful LED grow lights are more intense and can be placed further away, sometimes 18 to 24 inches. However, highly demanding species may require a distance as close as 4 to 8 inches.
The precise distance depends entirely on the light fixture’s power output and the plant’s specific needs. Using an automatic timer is the most practical way to maintain a consistent light schedule. Consistency is key to regulating the plant’s metabolic functions and ensuring the exact number of hours needed.
Observing succulents for physical changes is the best method for fine-tuning the light duration and distance. If the plant is receiving too little light, it will show signs of etiolation, or stretching. This appears as pale, elongated stems with widely spaced leaves, as the plant attempts to reach a brighter source.
Conversely, signs of too much light include a bleached or washed-out appearance on the leaves, which can precede a sunburn that manifests as crispy brown or white patches. For some varieties, an appropriate level of light stress will cause the plant to develop vibrant red, purple, or pink pigmentation, which is a desirable protective response. Monitoring these visual cues allows adjustment of the light duration or distance until the plants exhibit compact growth and healthy coloration.