House plants have holistic effect

01:12, Jul 09 2014
House plants
Studies suggest plants can have a positive psychological effect on us.

Winter is generally a time of rest in the garden, but it's an opportune time to turn your attention to indoor plants.

Plants grown indoors can satisfy an itchy green thumb, though you might also consider their benefits on your psyche.

Not only do plants serve as a cost-effective way to improve air quality, studies suggest they can also have a positive psychological effect on us. In a report on space psychology (Bates and Marquit 2011) the authors report, "There is mounting evidence from various academic disciplines that nature, and experiences with nature have a restorative impact."

The report goes on to say that: "Some of these 'restorative responses' include stress reduction, anger reduction, and an overall restoration in energy and well-being."

We do seem to have an affinity to nature - just think how calming and restorative it is to potter around in the garden. Even pulling out weeds can lead to a sense of achievement for some (though not all of us like weeding).

The same can be said for the home or indoor environment. A report by Lohr et al (1996) suggests that interior plants may improve worker productivity and reduce stress in a windowless environment.


"Interaction with plants, both passive and active, can change human attitudes; behaviours, and physiological responses. The stress-reducing benefits of passively viewing plants in natural settings are well documented; however, many workers labour in windowless office spaces with few opportunities to view nature. Research indicates that workers in such windowless environments have lower job satisfaction and rate the physical conditions of their work as less 'pleasant and stimulating' than people in windowed settings."

Dr Tim Jenkins of the Centre for Sustainable Agricultural Technologies in Christchurch says he has always been keen on having house plants for the aesthetics and filtering air.

"Psychological benefits can come from their visual presence and effect on interior air quality but also from the act of caring for them," he says.

"There is much published on the benefits of horticultural therapy. Bates and Marquit (2011) review some of these benefits. They mention house plants and specifically a successful trial of assigning elderly residential care people the duty of caring for house plants, with reported benefits in alertness, active participation and wellbeing."

There are many more reports to the same effect.

"Park and Mattson (2008) conducted an experiment with patients recovering from surgery by having paired rooms," says Jenkins, "one of which had plants and the other not, but patients were not told of the nature of the experiment and were not coached to care for the plants or pay attention to them. They reported multiple significant benefits from the presence of house plants."

Jenkins says it's possible that a psychological benefit may also come from the effect of plants on air quality. Research shows that the air we breathe indoors is typically polluted with volatile organic compounds (VOCs), which is released from carpets, paints, plastics, glues and computers, among other things. These VOCs have shown to cause symptoms such as headaches, loss of concentration and sore eyes, nose and throats.

Research by the National Aeronautics and Space Administration (Nasa) on the effects of house plants combating pollution consistently showed that houseplants removed up to 90 per cent of chemicals from the air, with some plants removing more than others. These pollutant- absorbing plants included aloe vera, anthurium, peace lily (Spathiphyllum), chrysanthemum, dieffenbachia, Dracaena marginata, Dracaena deremensis, Ficus benjamina, mother-in-law's tongue (Sansevieria), spider plant (Chlorophytum comosum) and umbrella tree (Schefflera), among others.

"There are numerous scientific papers published on the effect of plants on air quality and these can indeed be well designed and accurately measured," says Jenkins. "A Portugese experiment on a school's interior air quality (Pegas et al, 2012) found dramatic decreases in carbon dioxide and volatile organic compounds with house plants present."

The Pegas et al report also said that Wolverton et al (1984; 1985; 1989) placed potted plants inside sealed Plexiglas chambers, injecting substances commonly found in indoor air. The results showed that leaves, soil, and plant- associated micro-organisms serve an important function in reducing indoor air pollutants such as cigarette smoke, organic solvents, and bio-aerosols.

So don't give up on your garden this winter. Simply turn your attention to indoors.


Stop feeding plants altogether in winter unless they are cool-season bloomers.

Reduce watering. The biggest reason for plant failure over winter is due to too much moisture. Water only when the soil is dry. Poke your finger into the soil medium. If the bottom two- thirds of the pot is still wet, don't water. Your plants will tell you when they're getting too much water. Lower leaves turn yellow and drop off or brown spots may appear. Plants may also wilt. If roots remain consistently soggy, they'll turn to mush and plants will die.

Move plants closer to sunny windows during the day and away from cold drafts at night. But don't butt a plant right up to a freezing cold night-time window.

Most indoor plants like humidity, but heaters and dehumidifiers quickly dry out the air. Group potted plants together, or place individual pots on saucers of damp gravel to increase humidity levels.

The Southland Times