Houseplants are becoming more popular and there are many health benefits ascribed to them. Unfortunately most of these claims are not true.
In this post I will review our current understanding of the health benefits of houseplants.
DO Plants Purify the Air in Our Home?
There are millions of websites that say plants will reduce VOC (volatile organic compounds) levels in our home. A lot of the reports base their conclusion on an old NASA study that looked at this effect in very small chambers. I have discussed how this myth developed in some detail. NASA never studied plants in the home and never made plant recommendations for cleaning air in our homes – reporters made all that up.
A TED Talk by Dr. Meattle is also referenced a lot, but the claims made in this video are not supported by the government report that studied the facility.
A more recent paper reviewed all of the current studies and concluded that plants do not remove VOCs in our home. The air exchange through cracks in our home have a much larger effect than hundreds of plants.
The science on this subject is quite clear. Plants do not purify the air in our home.
Do Plants Add Oxygen to Our Air?
Most gardeners know that plants take in CO2 and give off O2 during the day while they photosynthesize. This is true and seems like a good thing.
What many don’t realize is that plants also absorb O2 and give off CO2, mostly at the root level, and that this occurs 24 hours a day. The other important factor is that humans use huge quantities of O2 compared to what plants produce.
The net effect is that plants do not increase the oxygen level in our home.
A recent critical review of the current literature on this subject focused on emotional states, pain perception, creativity, task-performance, and indices of autonomic arousal. They found mixed results. Some studies showed a benefit and others did not. There may be some effect for pain management.
Claims such as these, which are common on the internet, “studies have proven that house plants improve concentration and productivity (by up to 15%), reduce stress levels, and boost your mood”, are simply not true. People making these claims have cherry-picked the one study that showed positive results and ignored all of the studies that showed no benefits.
The results seen in this type of research depends very much on how the experiment is conducted. I think that we can conclude that there may be some benefit, but more research is needed.
Do Plants Increase Humidity?
Plants absorb water through the roots and expel it from the leaves. Only a small amount of the water remains in the plant. Since plants are adding this water to the air, some argue that they increase the humidity in air.
How much water is this? Say you add a cup of water to your plant every 4 days, which is 60 ml a day. As this water evaporates from the leaves it gets dispersed throughout the home. That is an insignificant amount of water, especially considering that the air in your home is continually replaced by outside air.
Most discussions about houseplants and humidity center around a lack of humidity and ways to increase the humidity for the plants. This would not be an issue if they increased the humidity on their own.
Plants do increase the humidity level but by an insignificant level.
As an aside, pebble trays holding water also increase humidity but do nothing for the plants since the evaporated water quickly spreads throughout the house.
Plants Make You Feel Better
That is probably true or you would not spend the time and effort to care for them. If you enjoy plants use them, because you enjoy them. But don’t believe all the hype you see on the internet.