Indoor plants for pollution control 

C    . Prabakaran

S.Jeeva

D. Saraladevi

A. Sabir Ahamed

V. Lakshmanan

A houseplant is a plant that is grown indoors in places such as residences and offices, namely for decorative purposes, but studies have also shown them to have positive psychological effects. They also help with indoor air purification, since some species, and the soil-dwelling microbes associated with them, reduce indoor air pollution by absorbing volatile organic compounds including benzene, formaldehyde and trichloroethylene. While generally toxic to humans, such pollutants are absorbed by the plant and its soil-dwelling microbes without harm.

    Common houseplants are usually tropical or semi tropical epiphytes, succulents or cacti. Houseplants need the correct moisture, light levels, soil mixture, temperature and humidity. As well, houseplants need the proper fertilizer and correct-sized pots

Houseplants are generally grown in specialized soils called potting compost or potting soil. A good potting compost mixture includes soil conditioners to provide the plant with nutrients, support, adequate drainage, and proper aeration. Most potting composts contain a combination of peat and vermiculite or perlite. Plants require soil minerals, mainly nitrate, phosphate, and potassium. Houseplants do not have a continuous feed of nutrients unless they are    fertilized regularly. Phosphorusis essential for flowering or fruiting plants and potassium is essential for strong roots and increased nutrient uptake.

House plants are generally planted in pots that have drainage holes in the bottom of the pot to reduce the likelihood of over watering and standing water. A pot that is too large will cause root disease because of the excess moisture retained in the soil, while a pot that is too small will restrict a plant's growth. Generally, a plant can stay in the same pot for two or so years. Pots come in a variety of types as well, but usually can be broken down into two groups: porous and non-porous. Porous pots provide better aeration as air passes. 

laterally through the sides of the pot. Non-porous pots such as glazed or plastic pots tend to hold moisture longer and restrict airflow.

Effect on indoor air pollution

Indoor plants reduce components of indoor air pollution, particularly volatile organic compounds (VOC) such as benzene, toluene, and xylene. These VOC's have been reported to reduce by about 50-75% with the presence of a houseplant. The compounds are removed primarily by soil microorganisms. Some tests of benzene purification by houseplants noticed that plants can makeup and convert benzene, then transform it to a carbon use for future use. Plants can also remove carbon dioxide, which is correlated with lower work performance, from indoor areas. The effect has been investigated by NASA for use in spacecraft. Plants also appear to reduce airborne microbes and increase humidity.

VOCs are more common in indoor areas than outdoors. This is because air and VOCs get trapped in indoor spaces; there is less air circulation. There are over 350 known VOCs. They are causative agents for “building  related illness” or “sick-building syndrome”. Symptoms of this illness include: irritated eyes, nose or throat, headache, drowsiness and breathing problems. These symptoms may not always be present, however, and chronic exposure may lead to lack of concentration and other health issues such as asthma and heart disease. Urban dwellers spend up to 90% of their time indoors so they are at higher risk of experiencing the adverse effects of indoor air pollution.

Common plants used to remediate indoor air pollutants include: English ivy (Hedera helix), Peace lily (Spathiphyllum ‘Mauna Loa’), Chinese evergreen (Aglaonema modestum), Bamboo palm (Chamaedorea seifrizii), and Chrysanthemum (Chrysanthemum morifolium). There are several studies that cite the plant microcosm as a mechanism to reduce indoor VOCs. The roots of indoor houseplants have also been proven to remove VOCs. In general, plants have to suck up the pollutant with their stomata during gas transfers to remove the VOCs. Controls of just pots alone and just a tray of water suggest that it is the soil microcosm that provides the pollutant sink. The role of the plants is to establish and maintain the species-specific root-zone microbial communities. This mechanism was first suggested by Wolverton et al. in 1985. Houseplants also aid in humidity, temperature, and noise control.

 transfers to remove the VOCs. Controls of just pots alone and just a tray of water suggest that it is the soil microcosm that provides the pollutant sink. The role of the plants is to establish and maintain the species-specific root-zone microbial communities. This mechanism was first suggested by Wolverton et al. in 1985. Houseplants also aid in humidity, temperature, and noise control

  NASA conducted a two-year study in 1989 to test the ability of houseplants or potting soil to remove several VOCs from the air. The experiment included the chemicals benzene, TCE and formaldehyde. The study was conducted in airtight experimental chambers. They found that bacterial counts correlated with increased chemical removal. Another finding was that when the same plants and soil were constantly exposed to a chemical such as benzene, their capacity to clean the air increased over time. This is because microorganisms have the ability to genetically adapt. Therefore, they change over time in order to utilize the toxic chemicals more efficiently as a food source. This phenomenon is used as a strategy to treat wastewater

Psychological effects

A 2015 study showed that active interaction with houseplants "can reduce physiological and psychological stress compared with mental work" A critical review of the experimental literature concluded "The reviewed studies suggest that indoor plants can provide psychological benefits such as stress-reduction and increased pain tolerance. However, they also showed substantial heterogeneity in methods and results. We therefore have strong reservations about general claims that indoor plants cause beneficial psychological changes. It appears that benefits are contingent on features of the context in which the indoor plants are encountered and on characteristics of the people encountering them. 

The phenomenon of biophilia explains why houseplants have positive psychological effects. Biophilia describes humans’ subconscious need for a connection with nature. This is why gardening and spending time outdoors can have healing effects. Having plants in indoor living areas can have positive effects on physiological, psychological and cognitive health. There is an architectural design approach known as “complexity and order” that coincides with biophilic design. Complexity and order is defined as, “the presence of rich sensory information that is configured with a coherent spatial hierarchy, similar to the occurrence of design in nature” Humans enjoy looking at things that are not boring but also not too complex. This design strategy is based on nature and human's  response to designs in nature. The presence of plants and nature-inspired designs "is restorative and not dull like the modern cookie cutter designs"

List of common houseplants

Tropical and subtropical

Calathea makoyana

Ficus benjamina variegate

Pilea peperomioides

Begonia cucullata

Aglaonema (Chinese evergreen)

Alocasia

Anthurium

Aphelandra squarrosa (zebra plant)

Araucaria heterophylla (Norfolk Island pine)

Asparagus aethiopicus (asparagus fern)

Aspidistra elatior (cast iron plant)

Begonia species and cultivars

Bromeliaceae (bromeliads)

Calathea (prayer plants)

Chamaedorea elegans (parlor palm)

Dypsis lutescens (areca palm)

Chlorophytum comosum (spider plant)

Citrus, compact cultivars such as the Meyer lemon

 Cyclamen

Dracaena

Dieffenbachia (dumbcane)

Epipremnum aureum (golden pothos)

Ficus benjamina (weeping fig)

Ficus elastica (rubber plant)

Ficus lyrata (fiddle-leaf fig)

Hippeastrum

Hoya species

Mimosa pudica (sensitive plant)

Nephrolepis exaltata cv. Bostoniensis (Boston fern)

Orchidaceae (orchids)

Cattleya and intergeneric hybrids thereof (e.g. Brassolaeliocattleya, Sophrolaeliocattleya)

Cymbidium

Dendrobium

Miltoniopsis

Oncidium

Paphiopedilum

Phalaenopsis

Peperomia species

Philodendron species

Maranta (prayer plant)

Monstera (Swiss cheese plant)

Sansevieria trifasciata (mother-inlaw's tongue)

Schefflera arboricola (umbrella plant)

Sinningia speciosa (gloxinia)

Spathiphyllum (peace lily)

Stephanotis floribunda (Madagascar jasmine)

Streptocarpus, including Streptocarpus sect. Saintpaulia (African violets)

Tradescantia zebrina (purple wandering Jew)

Pilea peperomioides

Scindapsus pictus (satin pothos)

Yucca species