Succulents are defined by their fleshy leaves and stems, adapting to arid environments by storing water. Like all plants, they perform photosynthesis, converting carbon dioxide and water into sugars while releasing oxygen as a byproduct. Succulents do produce oxygen, but their timing and mechanism of gas exchange are distinct from most common houseplants. This specialized metabolic pathway allows them to manage the harsh trade-off between gaining carbon and losing water.
How Standard Plants Manage Gas Exchange
The majority of plant species use C3 photosynthesis, where gas exchange occurs almost entirely during daylight hours. These plants rely on tiny pores on their leaves, known as stomata, which open when the sun is shining. Opening the stomata allows the plant to take in carbon dioxide (CO2) from the atmosphere for use in the photosynthetic light and Calvin cycles.
Oxygen (O2) is released back into the air as a waste product of this daytime process. However, this daytime gas exchange comes with a significant cost in hot, dry climates. When stomata are open, water vapor escapes through transpiration, leading to substantial water loss. This high water-loss rate prevents C3 plants from surviving in environments with intense heat or prolonged drought.
The Succulent Difference: Crassulacean Acid Metabolism
Succulents circumvent excessive water loss by employing Crassulacean Acid Metabolism (CAM). This adaptation separates the phases of gas exchange by time. The core strategy is keeping the stomata tightly closed during the hot, dry daytime hours when water loss would be greatest.
The plant opens its stomata only at night, when temperatures are cooler and humidity levels are higher, significantly reducing transpiration. During these nighttime hours, CO2 is absorbed and fixed into a four-carbon organic acid, typically malic acid. This malic acid is stored in large quantities within the plant cell’s central vacuole.
Once daylight arrives, the stomata close completely, sealing the plant against water loss. The stored malic acid is transported out of the vacuole and broken down (decarboxylated) to release the stored CO2 internally. This concentrated CO2 is fed into the Calvin cycle, combined with sunlight energy to produce sugar, and releases oxygen as a byproduct. This temporal separation ensures the plant can photosynthesize and produce oxygen during the day while conserving water.
Oxygen Output and Indoor Air Quality
The unique CAM cycle means that while the plant absorbs carbon dioxide at night, oxygen is still primarily generated during the day. The common belief that succulents release oxygen at night is a simplification, as the actual oxygen-producing steps are light-dependent. Because the oxygen is produced internally, it is not immediately vented into the room, though some is released via the pores throughout the day.
The overall volume of oxygen produced by a typical house succulent remains relatively small compared to a large C3 houseplant. Succulents are slow-growing and prioritize water conservation over rapid biomass production, meaning their total gas exchange is modest. Therefore, their contribution to significantly increasing the oxygen level in a room is minimal.
The greater benefit of having succulents indoors relates to air quality beyond simple oxygen production. Certain succulents, such as the snake plant, have been shown to remove trace amounts of volatile organic compounds (VOCs) like formaldehyde and benzene from the air. Additionally, the slow rate of transpiration helps regulate indoor humidity levels, offering a small benefit in very dry environments.