Indoor plants, air quality and a (nearly) foolproof way to keeping houseplants alive

A recent Facebook post by Viral Pulse brought up an experiment from 2005 about some wild abilities of English Ivy.  Ryan Kim, a teenager at the time, placed moldy bread and canine fecal matter inside containers and measured the particulate levels. After adding English ivy to the same containers, he again measured particulate levels at baseline, six-hour and 12-hour intervals.  The addition of the English Ivy reduced airborne mold by 78.5% and fecal particles by 94.25% over a 12 hour period.  He was assisted with the study and summary by Hilary Spyers-Duran of West Coast Clinical Trials in Long Beach, CA.  (English Ivy Removes Airborne Particulates)  These findings (non-peer-reviewed) were presented at the annual meeting of the American College of Allergy, Asthma, and Immunology that year.  Researchers also tested three air purifier brands in mold-infested homes. A Honeywell HEPA filter unit performed the best, clearing 72–84% of mold particles within one hour.  The English Ivy sounds very impressive, and cheap compared to HEPA filters!  How did it do this? 

First of all, there are two major ways plants can reduce air pollution: biofiltration and phytoremediation.  A biofiltration system is an ‘active’ living wall and can provide fresh air and temperature regulation in buildings. The active living wall could include a hydroponic system: nutrient-rich water is circulated in the system. Microbes in the root would remove volatile organic compounds (VOCs) in the air, and carbon monoxide and dioxide would be absorbed by the foliage. In addition, particulates in the air can be absorbed by the leaf surfaces.  Cold fresh air is drawn into the home by a fan. Therefore, one can use green facade systems for cooling and improving air quality. Compared with a ventilation air system, greenery systems are noticeably better at removing air pollution.  Below is a diagram of 2 types of living walls. (Current State of Indoor Air Phytoremediation Using Potted Plants and Green Walls)

Phytoremediation means using plants (trees, shrubs, grasses and aquatic plants and their associated microorganisms to delete, degrade or isolate toxic substances from the environment. There are different ways phytoremediation takes place, depending on the chemical matter and nature of the contaminant (such as an inactive substance or volatile or degradation matter in the plant or the soil) and the properties of the plant. Phytoremediation utilizes five different strategies to remove air pollutants, and plants can apply several strategies simultaneously.  These are:

• uptake of pollutants by the root from soil and water (this is phytoextraction and for air pollutants, it requires that air reaches the soil and roots), 

• Adsorbing gaseous pollution and particulates such as dust and bioaerosols by leaf surfaces, (this includes photosynthesis which removes CO2 and produce O2),

• Absorbing gaseous pollution by stomata (microscopic pores on the surface of plants, primarily leaves), which accumulate in various internal structures,

• VOC biodegradation can occur by bacteria growing on the plants, and

• enhancing humidity levels by leaf transpiration and evaporation from rooting media (soil, sediments, sludge, wastewater). 

The type of living wall system shown above can actually do both biofiltration and phytoremediation.  Although it was suggested afterward that the English Ivy removed the mold and fecal matter particulates mainly through the soil and roots, English Ivy has nice broad leaves with a waxy texture; these characteristics would make it a good candidate to remove particulate matter (PM) by catching it with the leaves. 

The amount of PM accumulation on the surface of the leaf depends on the placement of the plant in relation to the pollution source. (Air pollution abatement performances of green infrastructure in open road and built-up street canyon environments – A review) Usually, small PM attaches to a leaf surface better than large-sized PM; it also depends on the leaf shape and size, leaf arrangement, leaf surface hairs and cuticle (waxy layer). However, fine PM that land on a leaf can be easily re-suspended. For example, large PM and fine PM accumulated on the leaf of spider plants with the amount of 68% and 7%, respectively, in indoor environments. These rates were significantly higher than the amount of PM deposited on simple aluminum plates, showing that the plants’ ability to capture PM was not simply by gravitational force.  (Phytoremediation of particulate matter from indoor air by Chlorophytum comosum L. plants)  Another study showed the good potential for PM removal by spider plants in a green wall, and that the rate of airflow across the plants affects PM removal. In a range of 8.5 cfm to 32 cfm, the optimal airflow rate for PM removal was found to be approximately 23 cfm, with a removal efficiency up to 53 ± 10% (for reference, the average 120mm computer fan runs between 20-80 cfm).  This shows that steady, lower rates of airflow are enough to sweep particulates to the leaves but not too much to re-suspend them.

“Plant people” are aware of the ability of plants to remove particulate matter, because plants get dusty!  Now knowing that the “dust” could contain mold spores and fecal matter (yuck!), if you have plants, you’ll want to be more careful about how you remove the dust.  Dust removal in nature can be done by strong winds (no good indoors because it re-suspends the contaminants) or rainfall (a good option indoors if you place the plants in a shower or deep sink and gently spray them with cool water).  Another option is to gently use a HEPA vacuum cleaner with brush attachment, or gently wiping down the leaves with a damp paper towel, and disposing of the towel.

For those who wish they could reap the benefits of indoor plants for aesthetics and health (including better air quality) but find it hard to keep them alive…keep reading!

I’ve been pondering why I can’t seem to keep plants alive inside my house.  Is it my schedule or my interest in other things that prevents me from watering them on a regular basis?  On my dad’s porch about a quarter mile away, I’ve helped a dozen ferns, a peace lily, some succulents, and an orchid prosper with regular waterings.  They get watered with the remnants of the water buckets for the outdoor dogs, who get fresh water every day.  Basically, these plants get the attention they need because of the dogs.   The common denominator is water, and amazingly, some plants can live in water alone (with fertilizer or plant “food” every once in a while). 

Hydroponics and hydroculture (growing plants in only water) can be very simple!  There are several benefits that you get when growing in water: no under-watering, no over-water, no gnats, and no mold on soil!  You can start with a glass container and get some clippings to start roots growing on the clippings.  (Here is a super-easy way to “propagate” or root snake plants in water).  This is better than moving a plant that’s been growing in soil, to water, because “soil roots” are different from “water roots”.   Water roots are finer than soil roots, adapted to living in water alone.   Here are some more tips about growing plants in water from a very informative video and this article:

• You’ll need to change the water at least once a week so the roots will get new oxygen from the new water.  If there are things growing on the roots, you’ll need to rinse off the roots.  Rainwater is really good, but filtered water is fine too–municipal tap water is not great because it will probably have byproducts of chlorine in it.

• Add water-soluble fertilizer according to manufacturer recommendations. 

Here is a short list of plants that can survive in water long-term.

• Pothos

• Philodendrons

• Aeroids (I love calladiums and swiss cheese plants)

• Dracaena (including snake plants and lucky bamboo)

• Ferns

• Ficus

• Peace lilies

• Ivies (like English Ivy, beware that it is poisonous to pets and children and can cause dermatitis when touching it)

• ZZ plants (Zanzibar Gem)

Now, if you are able to keep more than 1 plant alive in water (or soil), you can start to add to them for visual interest, and then group them together using a repurposed shoe rack or baker’s rack, and place a low-speed fan in front to simulate the living air purifier above! 

Photo by Jeremy Lee on Unsplash