Do flowers take oxygen from a room? Unpacking the Science

September 28, 2025 •

3 min read

An age-old misconception suggests that flowers and houseplants can deplete a room's oxygen supply at night, potentially harming a person's health. The truth is that while flowers do take oxygen from a room during respiration, the amount is negligible and poses no threat to humans. Understanding the natural process of photosynthesis and cellular respiration is key to separating fact from fiction regarding indoor plants.

Quick Summary

The idea that flowers in a room can dangerously deplete oxygen is a myth rooted in a misunderstanding of plant biology. Plants respire day and night, consuming oxygen, but also photosynthesize during the day, producing far more oxygen than they consume. The minimal oxygen consumption by flowers is completely harmless, especially in a well-ventilated space.

Key Points

Respiration vs. Photosynthesis: While plants produce oxygen during the day via photosynthesis, they respire—and thus consume oxygen—24/7, though the amount is minimal.
Negligible Impact: The quantity of oxygen consumed by a typical flower or houseplant at night is too small to affect the air quality in a room or impact human health.
Human Impact is Greater: A human or pet in the same room consumes significantly more oxygen than any number of flowers could.
Airflow Matters: Rooms are not airtight, and natural air circulation and ventilation constantly replenish the oxygen supply.
CAM Plant Exception: Some plants like succulents and orchids use a different metabolic pathway (CAM) and can actually release oxygen at night.
Net Positive Effect: The overall benefit of having plants indoors, including air purification and mood enhancement, far outweighs any perceived negative from their minimal nighttime oxygen use.

The Science Behind Photosynthesis and Respiration

To truly understand the dynamic of gas exchange between flowers and their environment, we must first look at the two primary processes at play: photosynthesis and cellular respiration. These two biological reactions are opposite but complementary.

Photosynthesis: The Day Shift

During the day, in the presence of light, plants perform photosynthesis. This is the process where they use sunlight to convert carbon dioxide ($CO_2$) and water ($H_2O$) into glucose (sugar) for energy, releasing oxygen ($O_2$) as a byproduct. This is why plants are so vital to our planet's atmosphere, acting as the primary producers of the oxygen we breathe. For most plants, this process only occurs when light is available.

Cellular Respiration: The 24/7 Energy Burn

Unlike photosynthesis, which requires light, cellular respiration occurs 24/7. It's the process by which all living cells, including those in flowers and plants, break down the glucose produced during photosynthesis to release energy for growth and other metabolic functions. This process consumes oxygen ($O_2$) and releases carbon dioxide ($CO_2$) and water ($H_2O$), similar to human respiration. This is the source of the myth: the fact that plants consume oxygen at night when photosynthesis has stopped.

The Insignificant Oxygen Consumption

While the science confirms that flowers and plants do consume oxygen at night, it's crucial to understand the scale of this consumption. The amount of oxygen a few flowers or houseplants use is infinitesimally small compared to the vast amount of oxygen in a room and the air exchange that naturally occurs.

A Quantitative Perspective

Consider the numbers. A human being, for instance, consumes significantly more oxygen in a single breath than a moderate-sized houseplant does over an entire night. Even a pet sleeping in the room will consume exponentially more oxygen than a bouquet of flowers. The air in our homes is not static; it is constantly exchanged with the outdoors through ventilation, doors, and windows. This continuous air circulation means any minute oxygen reduction by plants is immediately replenished.

The CAM Plant Exception

Some plants, particularly succulents and orchids, utilize a process called Crassulacean Acid Metabolism (CAM). These plants have adapted to dry climates by opening their stomata (leaf pores) at night to absorb $CO_2$ and store it. They then perform photosynthesis during the day with their stomata closed, minimizing water loss. As a result, CAM plants can actually release oxygen at night, further debunking the myth that all plants are oxygen 'thieves' in the dark.

Comparison Table: Plants vs. Humans


Feature	Plants (Photosynthesis)	Plants (Respiration)	Humans (Respiration)
Requires Light?	Yes	No	No
Consumes Oxygen?	No	Yes	Yes
Releases Oxygen?	Yes	No	No
Consumes Carbon Dioxide?	Yes	No	No
Effect on Room Air	Increases oxygen slightly	Decreases oxygen slightly	Decreases oxygen significantly

The Benefits of Having Flowers and Plants Indoors

Beyond the negligible oxygen factor, the benefits of having plants and flowers indoors far outweigh any imagined negatives. Studies have shown they can improve mood, reduce stress, and potentially boost overall health.

Psychological and Aesthetic Benefits

Flowers and plants can be a great source of comfort and beauty. They connect us to nature, even when we are indoors, which can lead to a sense of well-being. Patients in hospital rooms with flowers have been shown to require less pain medication and have lower blood pressure, suggesting a positive psychological effect.

Air Purification

Certain houseplants are also known for their air-purifying qualities, absorbing harmful pollutants like formaldehyde and benzene from the air. While the effect is not as dramatic as an air purifier, it contributes to overall indoor air quality.

Conclusion: A Harmless Myth

To conclude, the notion that flowers or houseplants can consume enough oxygen to pose a health risk is a myth. The amount of oxygen consumed during plant respiration is tiny and easily offset by the oxygen they produce during the day, as well as regular ventilation. Instead of fearing your flowers, embrace their presence. They offer aesthetic beauty, psychological benefits, and even mild air purification, making them a welcome addition to any indoor space. If you're looking for more information on plant biology, the Royal Horticultural Society provides excellent resources on how plants function [https://www.rhs.org.uk/advice/understanding-plants/how-plants-breathe].

Frequently Asked Questions

No, it is not dangerous. The amount of oxygen consumed by flowers at night is insignificant and poses no threat to a sleeping person. The concern is based on an old myth.

No, they do not. While plants respire and consume oxygen at night, the amount is so small that it is completely harmless. Your own breathing has a far greater impact on the oxygen levels.

Most flowers do not. Photosynthesis, the process that releases oxygen, only happens in the presence of light. At night, most plants switch to respiration, consuming oxygen. However, some special plants like orchids can release oxygen at night.

It would require an enormous number of plants in an airtight, completely sealed environment to noticeably decrease oxygen levels. In a normal home, with natural ventilation, this is not a concern.

Photosynthesis is the daytime process where plants use sunlight to create food and release oxygen. Respiration is the 24/7 process where plants use oxygen to break down that food for energy, releasing carbon dioxide.

Yes, there are. Flowers and plants have been shown to improve mood, reduce stress, and even contribute to better indoor air quality by filtering some pollutants.

CAM (Crassulacean Acid Metabolism) plants are a group including succulents and orchids. They are special because they open their pores at night to take in carbon dioxide, which allows them to release oxygen at night, an adaptation to arid environments.