Succulents are a diverse group of plants characterized by thick, fleshy parts, which they use to store water. These unique water-storing capabilities allow them to endure long periods of drought, making them popular and resilient houseplants. They cannot survive without light itself, as it is their energy source, but they can thrive without direct natural sunlight if a suitable alternative light source is provided.
How Succulents Utilize Light
Light is the fundamental energy source for succulents, fueling photosynthesis. Succulents employ a specialized survival strategy known as Crassulacean Acid Metabolism (CAM photosynthesis), a key adaptation to dry environments. This process involves a temporal separation of gas exchange and carbon fixation to conserve water.
During the night, when temperatures are cooler and humidity is higher, the plant’s leaf pores (stomata) open to absorb carbon dioxide. The carbon dioxide is converted into organic acids, such as malic acid, and stored within the plant’s cells. When the sun rises, the stomata close tightly to prevent water loss, and the stored malic acid is broken down to release the carbon dioxide internally.
The light energy absorbed during the day powers the rest of the photosynthetic process, converting the released carbon dioxide into sugars for growth. For many sun-loving varieties, the light intensity needed to properly drive this daytime process is quite high. Optimal growth requires light levels between 3,000 and 5,000 foot-candles (FC).
This high requirement explains why a dimly lit corner, which may seem bright to the human eye, is often inadequate for a succulent’s energy needs. For context, a typical well-lit office space might only register 40 to 50 foot-candles, while a bright outdoor sun can exceed 10,000 FC. Succulents need intensity closer to the high end of this range to maintain their compact form and vibrant colors.
Physical Indicators of Light Deprivation
When a succulent is not receiving the necessary light intensity, it begins to display specific physical changes as it attempts to find more light. The most common sign is etiolation, or “stretching.” This occurs when the stem elongates rapidly, and the spaces between the leaves (internodes) become noticeably wider.
The new growth will appear much paler or a lighter shade of green than the older, established leaves because the plant is maximizing its surface area to capture available light, diverting energy away from producing dense pigments. The plant’s structure becomes weak and floppy, struggling to support the weight of the leaves. The typically tight rosette shape of plants like Echeveria will flatten or open up.
In varieties that naturally exhibit vibrant “stress colors” such as reds, purples, or oranges, these colors will fade and revert to a duller green. These protective pigments are only produced under high light intensity, and their disappearance signals inadequate light exposure. If the problem persists, the lower leaves may yellow and drop prematurely as the plant conserves energy.
New leaves that appear in low light conditions are often smaller and thinner than the older foliage. This reduced leaf size indicates that the plant lacks the energy reserves to produce healthy, full-sized structures. Recognizing these indicators early allows a grower to correct the situation before the plant’s health is severely compromised.
Using Artificial Light Indoors
The most effective solution for growing succulents indoors without sufficient natural sunlight is specialized artificial lighting. The ideal option is a full-spectrum LED grow light, engineered to emit wavelengths across the entire visible light spectrum, closely mimicking natural sunlight. This comprehensive spectrum supports all aspects of plant health, including vegetative growth and flowering.
These full-spectrum lights contain both blue and red wavelengths, which are particularly important for plant development. Blue light promotes compact, sturdy growth and thick leaves, helping to prevent stretching. Red light is primarily responsible for encouraging blooming and overall plant height.
Succulents require a substantial duration of artificial light, typically between 10 and 16 hours per day to complete their photosynthetic cycles. This cycle must be followed by a period of darkness (usually 8 to 14 hours) to allow the nocturnal gas exchange part of their CAM metabolism to occur.
The distance between the light source and the plants is a critical factor in delivering the necessary intensity. For fluorescent tube lights, a distance of 6 to 12 inches above the plant tops is often recommended. LED grow lights, which can be more powerful, generally need to be positioned slightly further away (12 to 24 inches) to provide high intensity without causing leaf burn.