Plants can talk. For a long time, that belief was dismissed as woolly nonsense. But the more we come to know about plants and their properties, the more scientists are becoming convinced that plants really can communicate. And they do that quite ingeniously. Plants pick up signals from their surroundings, process that information and convert it into solutions to enable them survive. As Darwin would say: plants are intelligent. Plants and people actually have surprisingly much in common.

Plants are often deemed the lowest in the ranking of living organisms. Many languages have such expressions as ‘vegetating (like a plant)’, meaning leading a meaningless, soulless life. Yet even in ancient times the question of whether plants ‘had souls’ was much discussed and over the centuries various philosophers and scientists have repeatedly claimed that plants are social organisms and attributed them with certain skills. Until recently, however, this could not be proven and their claims were dismissed as figments of their imagination. Or as science fiction, like in the well-known film Avatar where the inhabitants of Pandora, a planet in the distant future, believed neuron-like electrochemical connections existed between the roots of trees and plants, which collectively formed a nervous system that covered the entire planet, and had a consciousness. Gaia 2.0.

However, recent years have seen the publication of ever more studies which establish the intelligence of plants on the basis of extensive and serious scientific research, and even the emergence of a new field of research: plant neurobiology.

The advantage and disadvantage of being rooted

One of the main differences between plants and humans or animals is the the first group cannot move. If we are hungry we go looking for food, if we sense danger we run away or make a loud noise. We move house if we think we could find a better job elsewhere or when adventure beckons. Plants cannot do any of those things; they are rooted, bound to one spot and therefore completely dependent on their environment. In order to survive, therefore, they had to develop other, sensory mechanisms. And they did. These mechanisms are now known to be highly complex and refined.

Brilliant Green

One of the strongest advocates of plant intelligence is plant physiologist Stefano Mancuso of the International Laboratory of Plant Neurobiology. In the book ‘Brilliant Green’ he and his co-author, scientific journalist Alessandra Viola, reach the conclusion that plants are actually even more intelligent than humans. Whereas we only have five senses, they have more than twenty. Which they use very efficiently.

One of the key characteristics of plants, according to Mancuso and Viola, is that they have a modular structure. That is to say that while each part of a plant is important to its survival, it is not indispensable. The vital functions of a plant are not centralised in single organs; the whole plant functions as a kind of super organism. Some plants can be almost completely eaten away yet still recover.

Advanced senses

Plants can ‘see’. Light, the main ingredient of their energy diet, is vitally important. Not only are plants able to capture and utilise light; via light receptors, found all over the plant but especially on the leaves, they are also able to recognise the quality of the light and to adapt their growth habit accordingly.

Plants can also smell. Plants are covered with receptors for volatile substances. They transmit a chain of signals, passing on information to the whole organism. Plants use ‘scents’ or chemical compounds to interact with their surroundings and with insects. They absorb messages and also release them, when they are exposed to stress, for example. A plant that has been eaten into, will disperse molecules to warn conspecifics in its vicinity of the danger. These neighbouring plants will subsequently produce chemical substances to make their leaves inedible or toxic. The senses of smell and taste are just as closely related in plants as they are in humans and animals.

Plants can taste. In plants, the organ of taste consists of receptors for the chemical substances they feed on. The roots search for these substances in the soil. Plants taste nitrates, phosphates and potassium with their roots, and can locate minimal quantities even at long distances. They do this by allowing their root system to keep growing until all the substances have been absorbed. If the roots encounter substances which are toxic to the plant, however, they will move as far away from them as possible.

Plants also have a sense of touch; such as the well-known ‘touch-me-not’ whose leaves close when touched. It is interesting that this does not happen if a drop of water falls onto it and that the leaf will open again if a stimulus is not or no longer dangerous. Carnivorous plants only close when certain insects land on the leaf, other plants trap insects until they are completely coated in pollen and then they release them again. Many plants demonstrate their sense of touch by winding round objects, enabling them to grow vertically.

Plants can also hear. That is to say: they sense sound vibrations. And they respond to them too. An Italian winegrower, for example, grew his grapes to the sound of music. The results were astounding: the grapes grew faster, were healthier and tasted better.

Plants have developed many more senses besides these five; senses plants can use to their advantage because they cannot move. Senses which enable them to measure the moisture content in the ground, sense gravity and electromagnetic fields, and recognise and measure numerous chemical gradients in the air or soil. All aspects that are essential to their survival, growth and development.

Plants make use of electric, hydraulic and chemical signals to communicate both internally and externally. And make decisions accordingly. For example, in the middle of a hot day, plants can decide to close the stomata on their leaves. This stops them from photosynthesising. But it also stops them from dehydrating,  which then takes priority. They communicate externally by touching each other’s roots or leaves, for example, or by emitting molecules that contain information. Based on that information, a plant may decide to act hostilely or rather to form a symbiosis. Plants also communicate with animals, by producing an attractive or repulsive scent, for instance. Which they can do very cunningly. They are capable of emitting chemical substances that will attract their enemies’ enemies, such as a mite which will eat the mites that attacked the plant. Of course, their scents and colours also enable plants to attract insects and other animals in all kinds of ways, which then act as ‘pollen courier’. Thus ensuring their survival in another spot. Scientific journalist Michael Pollen described it poetically: ‘bees are the legs of plants’. The medium of exchange is usually nectar but some plants are even capable of fooling their visitors by changing shape, scent or colour. There is actually an orchid that can change to resemble a female insect ready to mate. So plants continually make decisions that can influence life or death.

The wood wide web: the benefits of exchange

Practically all plants have intimate relationships with fungi through their roots. Hyphal threads in the soil digest dead animals and plants and release this to plants in the form of carbon. In return, the plants provide the fungi with sugars. Both prefer to exchange with whichever gives them the most in return. So they make choices. The gigantic underground mycorrhizal network that interlinks plant roots, and can be many kilometres in diameter, is nicknamed the ‘wood wide web’. Plant biologist Suzanne Simard of the University of British Columbia, discovered that trees communicate with one another via fungi and that they share carbon and other nutrients with one another, even between different species. Birch trees exchanged CO² with spruce and at a different time in the season the same thing happened in reverse. She also discovered the important role ‘mother trees’ play in this web. These larger, older trees are the hub of the web, as it were, and control the nutrients of the whole network. Simard also discovered that mother trees feed their own saplings more carbon than other trees. It even appears that mother trees that are on the point of dying send extra carbon and defence signals to their saplings via the mycorrhiza network.

Plants as social organisms

Simard’s standpoint that forests are not merely collections of individual trees but resilient, social communities, is endorsed by former forester Peter Wohlleben. One day in the forest he discovered remarkable gnarled specimens, which at first sight resembled lifeless stones but were in fact the remainders of an ancient tree trunk that had been felled centuries ago. To his utter amazement, they turned out to still be alive, despite having no leaves and photosynthesis consequently and the uptake of nutrients thus being impossible. Further research revealed that the remainders were fed by the surrounding trees, via the roots. Apparently the forest would not benefit from losing these weaker members. For Wohlleben this event sparked a continuous fascination for the behaviour of trees.

Wohlleben describes trees in human terms; they can suffer pain, make friends, raise their children, collaborate, sorrow. They give each another space – a phenomenon so poetically described as ‘crown shyness’ – or shade, so that saplings can grow at the slow rate that is best for them.

His book ‘The Hidden Life of Trees’ was a bestseller in many countries. Wohlleben now manages his own forest, where trees are allowed to grow entirely as they please and where he gives people guided tours to introduce them to the wonders of the wooded world.

Do plants justice

That is perhaps the crux of the matter. Inspired by their fascination and wonder, Mancusco, Simard and Wohlleben are all passionate advocates of a different approach to the plant world. Based on the concept of symbiotic communication between plants, enabling a positive development of the whole ecosystem, we should show more respect for plants. And adapt our relationship with them and thus with the planet. Not only would that be more sustainable, it would also be in our own interest.
After all, plants, which account for 99% of the biomass on Earth, form the base of the food pyramid, give us the oxygen we breath and the energy we use, and mitigate the consequences of climate change. On top of which they are also able to detect and tackle substances that are harmful to us or to provide ingredients for medicines. As Mancuso and Viola maintain: the planet will survive without us.

The question is: will we survive without plants?

It is said we know more about the universe than about the soil beneath our feet. Thankfully, this is gradually changing. A healthy soil is full of life, literally. Full not only of tiny living creatures such as worms and wood louse, but also of micro-organisms such as fungi and bacteria. Together with plants, they make up a complex ecosystem in which all various organisms have a function of their own and support one another. Pot plants stand alone, however, because most potting soil is sterilised and consequently contains much less soil life. Both research and practice reveal that enhancing soil life in potting soil can benefit plants in many ways.

Symbiosis between plants and soil life

Just one teaspoon of woodland soil can contain a kilometre of hyphal threads. The soil of a healthy wood is a self-sufficient, living ecosystem. The fungi in the vicinity of the roots of plants and trees are called mycorrhiza. They live in symbiosis the rhizosphere (the vicinity of plants roots together with the rhizobacteria). The plant roots cannot reach all the nutrients (water and minerals) in the soil themselves. The fungi and bacteria help the roots reach and absorb the nutrients. They are also able to make phosphate available to the plant. But they expect something in return. The plants give the micro-organisms sugars (glucose). Thus creating a symbiosis. Rhizobacteria and mycorrhiza not only help plants to take up water and minerals; they also protect the plant against pathogens, pollution and drought. This symbiosis is like a marriage of convenience. If the plant is able to extract nutrients from fertilizer, it will immediately stop the exchange with the fungi.

Soil life in potting soil

The roots of indoor plants are also in soil. However, potting soil has been heated to eliminate pathogenic bacteria. With the result that most benign bacteria and fungi, which usually help and protect the plant, will also have been removed. What are the potential benefits of adding mycorrhiza fungi and rhizoacteria to potting soil?

Research into the benefits to plants of added micro-organisms

At Wageningen Plant Research, in 2014, Dr Joeke Postma researched the benefits of mycorrhiza for pot-grown strawberries. Strawberries are susceptible to root rot (Phytophthora cactorum). Dr Postma researched whether adding a certain mycorrhiza fungus (Rhizophagus irregularis) could protect the plant from this disease. She discovered this to be the case. This species of fungus proved able to reduce root rot infection by some 50%.

Postma concludes that healthy soil life is essential to healthy plant growth. “Particularly when plants are growing not in open ground (but in potting soil, rock wool or hydroponics, for example), there will be a lack of plant-specific micro-organisms in the rhizosphere. Adding these useful bacteria or fungi can enhance plant growth and protect plants against infection.” NB: the effectiveness will vary. Not all fungi or bacteria are equally useful for all plants.

In another, similar study Postma also researched the benefits of adding certain bacteria to tomato plants growing in potting compost. She selected to use the bacterium Pseudomonas chlororaphis strain 4.4.1, on account of its capacity to inhibit fungal growth and to enhance  phosphorus uptake by the plant. The number of healthy plants rose by 30 to 105% compared to the control group in three independent greenhouse experiments.

Pius Floris: “We should not think of mycorrhiza as pesticides”

Pius Floris is a soil specialist. He is familiar with Postma’s research into the effect of mycorrhiza on strawberries. “It is wonderful that a specific species of mycorrhiza can inhibit root rot in strawberries. However, we must not think of mycorrhiza fungi and bacteria as pesticides; they are not against anything”, he says during a telephone interview. “Mycorrhiza are just as much part of the plant as the foliage. There is a natural relationship between fungi, bacteria and the plant. The problem with scientific research is that it often produce an answer to a very limited research question. Studies do not often consider the entire plant ecosystem. I see mycorrhiza as a natural stress manager. Indoor plants are sometimes too wet, sometimes too dry. If the symbiosis between fungi, bacteria and plants is in balance, the plant will be much better able to survive too much or too little water. And anywhere that mycorrhiza live, no other pathogenic fungus can grow.”

“Fertilizers kill the soil and cause disease in plants”

Floris’ thesis is clear: a healthy soil produces healthy plants. The same applies to potting soil for indoor plants. Together with his team from Plant Health Cure he develops soil bacteria and soil fungi for sustainable crop growth in agriculture and horticulture and for nurseries. Floris: “In the cultivation of plants, indoor plants are often grown in hydroponics: clay pellets with water and fertilizer. That is supposedly convenient as it avoids the need to change the potting soil every year. But fertilizer has a very high salt content and salinization is not good for plants. Put simply: fertilizers kill the soil and cause disease in plants. If you add mycorrhiza and bacteria to the potting soil you need use less pesticide, or none at all, and less water.”

The application is very simple, Floris explains: “Mycorrhiza need only be added to the potting soil once. You simply make holes in the potting soil, dilute the mycorrhiza and bacteria mixture with water and pour it into the holes. Your plant will be more resilient and you will never need to change the potting soil. Unfortunately you will still have to fertilize pot plants, simply because they use up the minerals in the pot during growth. As opposed to garden plants which have much more growing space and thus more minerals available. So fertilizing remains essential, but do use organic liquid fertilizer. The bacteria and mycorrhiza ensure optimal conversion and absorption.”

The benefits of healthy soil life in potting soil:

• Plants will be ‘in balance’ thanks to the natural symbiois with mycorrhiza fungi and bacteria. As a result, they will be more resistant to disease, drought and excessive water.
• Micro-organisms in the potting soil make nutrients available which the plant would otherwise not be able to absorb.
• Synthetic fertilizers and pesticides are superfluous. Organic fertilizing is still essential.
• The potting soil does not need to be changed.

It is sustainable and environmentally friendly.

Guest author: Marjolein Bezemer

Plants are lovely to see – and they can raise your spirits, as well. But perhaps even more importantly: plants also play a very important role in ridding our surroundings of toxic substances. The world is becoming increasingly urbanised and dirty, in rapid tempo. In cities, smog forms a substantial problem, as do soil and water pollution. Luckily, though, green walls, green roofs and even green cities are on the increase and helping to purify our air, soil and water. The technical term for using plants as a means of cleansing the environment is phytoremediation.

Phytoremediation literally means: bringing our environment back into balance through the use of plants. It involves technologies which employ plants to purify the air, soil and water. Plants naturally absorb and remove contaminants. For example, a large number of plant species absorb volatile organic compounds from the air in our homes. They do this with their leaves and roots and the organisms in their (pot) soil, which in turn convert the compounds into food for the plants.

How does phytoremediation work?

There are a number a of ways in which certain plant species, together with the organisms in their soil, are able to cleanse  their environment. They help remove contaminants in tandem with a number of different processes:

Source: http://opensciencepublications.com/

• Plants are able to lock up contaminants in their roots, stems and leaves (phytostabilisation).
• Contaminated portions of plants can in turn be removed and destroyed (phytoextraction).
• Plants and organisms in the soil are able to convert toxic substances into less toxic ones; this occurs either within the plants or in their root zone (translocation).
• With their juices, plants are able to attract certain bacteria to their root zone, where toxic substances in the soil are either reduced or locked up (phytodegradation).
• Plants and organisms in the soil are able to convert toxic substances in the air into less toxic gases, which are in turn released back into the air (phytovolatilisation).
• Plants are able to fix toxic substances onto their roots, where microorganisms, such as bacteria, in turn break them down and convert them into less toxic substances (stabilisation in the root zone).
• Some plants draw polluted groundwater upwards, so that it cannot seep deeper into the soil (stabilisation).

In practice: plants and green walls improve our interior environment

Within our homes, the phytoremedial value of plants lies primarily in their ability to purify the air. By means of phytovolatilisation, plants remove toxic, volatile organic compounds from the air and use them as nutrients. In this way, plants can contribute substantially to improving air quality in our homes and offices. Increasingly, interior landscape designers are creating green walls for a healthier environment in such venues as schools and airports.

Schiphol Airport. Photo: Marjolein Bezemer

Plants and the bacteria and moulds they work with are not just extremely proficient in cleaning up volatile substances, but also absorb fine particulates. Research conducted in Poland (2014) showed, amongst other things, that the spider plant (Chlorophytum comosum L.) absorbs fine particulates. Large particulates, as well as the finest and, to human beings, most dangerous particulates are absorbed by this plant via its leaves and their wax layer.

This short film shows how easy it is for everyone to employ phytoremediation in their own home.

Plants purify soil and water

Whilst indoor plants are deployed primarily to purify the air, plants are now also finding wide use outdoors to purify contaminated soil and (ground)water. Willowtrees (Salicaceae) and a range of species of mustard plant (Brassica), for example, have the ability to absorb such heavy metals as cadmium, nickel and lead from the soil. Indian mustard (Brassica juncea L.) and a number of Amaranth cultivars are even being used in Chernobyl and the surrounding area to absorb the radioactive substance caesium 137 from the soil. Plants are not only able to fix or convert heavy metals and radioactive material – they can also filter out low concentrations of pesticides, explosives and oil from the soil. At urban playground De Ceuvel in Amsterdam North, experiments are being carried out into the use of plants to remediate the heavily contaminated bottom of an old shipyard. Amongst the plants being tried out are: the broadleef cattail (Typha latifolia), the foxglove (Digitalis purpurea) and the black willow (Salix nigra).

Beer brewery De Koningshoeven (makers of La Trappe) in the Dutch province of North Brabant is in the advanced stages of plans to purify its waste water by means of its own plant-based installation. In cooperation with water board De Dommel, the brewery intends  to construct a large glasshouse especially for this purpose. Tropical plants growing in the greenhouse are to be used to purify waste water and convert it into irrigation water. In this way, the brewery expects to reduce the amount of water used by 50%, as well as to demonstrate the efficacy of water purification through phytoremediation.

Plants purify the air outdoors

Plants are not just effective cleaners of the soil, water and indoor environment – they are also able to remove toxic substances from the air out of doors. Italian architect Stefano Boeri uses plants in his designs, with the aim of, amongst other things, improving the air quality in cities. The first of these ‘vertical forests,’ as Boeri refers to them, was a high-rise apartment building in Milan. Featuring 20,000 plants and 800 trees from more than a hundred different species, it can be compared to a piece of forest, two hectares in size, the only difference being that it is a building, with 1500 square metres of floorspace in the centre of a city. This vertical forest absorbs 40 tonnes of CO₂ and 1.5 tonne of fine particulates each year. As a ’bonus,’ it also generates 90 tonnes of oxygen per year, lowers the outside temperature, functions as a sound barrier and stimulates biodiversity. A similar tower, by the same architect, is soon to be erected in Utrecht, appropriately dubbed Wonderwoods.

Photo: Wonderwood – Stefano Boeri Architetti

Stefano Boeri was recently commissioned to build an entire city in the form of a vertical forest, in China: in 2020, 30,000 people will be living in the green city, Liuzhou, together with more than a million plants.

It is of course not possible to put up a green city at once, everywhere. But it is possible to modify existing buildings by adding green roofs in order to purify the outdoor air. Research published in 2008 showed that plants on green roofs in Chicago were truly able to remove a portion of the toxic substances in the air. The scientists involved in the study investigated the air purifying capacity of 19.8 hectares of roof greenery. In one year, a total of 1,675 kg of airborne pollutants had been absorbed by the plants. The researchers also calculated that in excess of 2,046 tonnes of toxic substances could be filtered out of the air if all roofs in Chicago were covered with thick plant growth.

Phytoremediation is proving be a highly effective method for restoring balance to our environment, both indoors and out. Can we expect plants, green walls, green roofs and entire green cities to spring up everywhere in the future? For the sake of our health, and that of the earth itself, that would in any case be a splendid prospect!

Guest author: Marjolein Bezemer

Clean air should be a human right. That is the essence of the corporate mission of the Finnish Naturvention in a nutshell. To fulfil that human right, the company has not only devised a revolutionary green wall that actively purifies indoor air – using their own operating system, Naava OS – it also markets the wall not as a product but as a 100% service, as a high-tech human right.

Naava lives at a fast pace

Naturvention’s innovative product is called Naava and is available in various sizes, types and capacities. The basic form is a 80×200 cm wall in which plants are planted without soil in such a way that a computer controlled ventilation system provides optimal air circulation around the plant roots. This is done on purpose because Naturvention states that it are the root microbes which are the key for natural air purification, not the leaves as one would think. The plants in the wall are consequently very active and purify the air extremely quickly. The Naava operating system monitors the amounts of light and water and the quality of the air continuously. A Naava wall uses between 5 and 12 litres of water a day and doing so optimizes air humidity quite well. The water is automatically pumped up from a tank at the base of the wall. By no means all plants are suitable for planting in this wall as some would then grow so rapidly that they would be impossible to maintain.

A service with a 100% satisfaction guarantee

We spoke to one of the founders, microbiologist and ICT specialist Niko Järvinen, and he explained that Naturvention does not actually market Naava as a product but as a service with a 100% satisfaction guarantee. Artificial intelligence plays a major part in delivering this promise. Naava is not a green wall, it´s not a thing, it’s a guarantee for clean air. Once sold, both the owner and Naturvention have access to a dashboard for the wall, an app that monitors the wall continuously and transmits a signal if anything is not as it should be. This enables Naturvention to offer a 100% quality guarantee. He also explained that 30% of Naava customers are from the education sector. This surprised us as the product isn’t cheap. Niko agreed, but added that they install the wall in a classroom for a free 14-day trial, and it is only after this trial period that they submit their offer. By which time most schools do not want to part with their wall. Also, if one considers that one Naava wall equals the purification power of 4000 houseplants, the price doesn’t seem expensive anymore.

How do you build a green business?

The company was founded in 2011 by three entrepreneurs, none of whom has a traditional green sector background. Number one has extensive experience in setting up businesses and teams, number two is an expert in ICT and microbiology and number three has very wide experience in sales. The company has since grown by at least 100% a year, now has a workforce of 40 and is currently rolling out both the business and its products internationally. All three founders are passionate about health and clean air, and all three are convinced that, above all, we should be building healthy businesses with meaningful aspirations and viable, significant, scalable products, a key element of which is fantastic service.

There has recently been a growing interest in incorporating nature into design and building, known in the jargon as “biophilic design”. It produces buildings which feel good and in which people feel better. And consequently perform better. In the workplace, for instance, it goes hand in hand with lower sickness absence rates and higher productivity. That’s fine for organisations. But what is the actual benefit in terms of euros? Developing a hard “business case” for green and healthy environments is harder than it might at first seem. Sustainability consultancy Terrapin Bright Green researched this for the United States and wrote a comprehensive report that could also prove a source of inspiration for the situation in the Netherlands.

In recent years, much research has been conducted into the welfare effects of biophilic design. Much less is known, however, about what those effects actually mean in monetary terms, because it is apparently difficult to define appropriate quantifiable indicators. While ever more organisations apply the principles of biophilic design with the aim of branding themselves as a sustainable company or creating a good workplace for their employees, few realise that there could also be a financial gain. A missed opportunity, according to Terrapin Bright Green. Much is to be gained, literally, especially in terms of productivity. Indeed, some 90% of all costs are staff-related expenses. Costs relating to sickness absenteeism or “presenteeism” amount to approx. 4%. As a comparison: energy costs are around 0.8%. The smartest investment economically, therefore, is in the human factor; small improvements in productivity or slight reductions in sickness absenteeism generate much more financial gain than energy savings, for example.

Workplace: sickness absenteeism and presenteeism

Many people spend more than 40 hours a week in their place of work. How productive those hours are is largely determined by how people feel in that workplace. An unpleasant or unhealthy workplace can lead to a lack of focus, a negative mood, health problems and sickness absenteeism. On average, the average sickness absenteeism at work in the US is more than 62 hours per employee per year, which equates to an average cost item of over 2,000 dollars per employee. Sickness absenteeism in the public sector is even higher, averaging 83 hours a year. The annual losses for larger organisations run into millions. Research conducted at the University of Oregon revealed that 10% of all sickness absenteeism is attributable to workplaces that have no direct or indirect relationship with nature. Staff with a window overlooking greenery took far less sick leave than employees without a green view. Other research revealed that a view of living green aided faster recovery from fatigue. An example: at ING head office in Amsterdam, designed with plenty of natural daylight, organic architecture, water, green and art (and completed in 1987), sickness absence rates fell by 15%. 

Besides absenteeism, an unpleasant or unhealthy working environment can also lead to presenteeism, where employees are present but lethargic and not focused. They are consequently less productive. The resulting cost item for larger organisations can amount to 100,000 dollars a year. The strategic positioning of the workplaces at a call centre in Sacramento proved to have amazing results. Employees with a large window overlooking greenery dealt with telephone calls 6-7% faster than their colleagues without a view. The initial outlay of the window and the slightly larger floor space requirement was recovered within four months. The long-term productivity increased, as did the profits. For a company with 1000 employees, a 6% rise in productivity could generate a profit of several million a year.

Healthy hospitals, healthy profit

Various studies have shown that patients recover more quickly in rooms with plenty of natural daylight and views of greenery. Shorter hospitalisation means lower costs for both hospitals and health insurers. Giving patients a room with a view of greenery could generate savings of 93 million dollars. Research in 2005 revealed that gall bladder surgery patients who stayed in a room with a lot of daylight took approx. 20% less medication than patients in a darker room. Such differences are relatively easily quantifiable in terms of money, based on the costs of the medication concerned. Healing hospital gardens reduce stress levels among patients as well as doctors and nursing staff. This has a positive effect both on the speed of patient recovery, which may in turn be related to the use of medication and length of hospitalisation, and on staff performance. The positive effect this would have on sickness absenteeism is rarely calculated, despite the significant savings this could generate per hospital, even when for the costs of constructing and maintaining the gardens are taken into account.

Stores sell more

The average American spends around 13,000 dollars in retail stores. Research has shown that people spend more money in shopping centres and retail environments that are light and green. In a consumer survey, participants who were shown pictures of a green shopping environment proved to consider food and clothing prices that were 20%-25% above normal, as acceptable. A survey among 73 stores in California revealed that stores which had skylights installed saw their sales figures increase by 40%. Daylight apparently boosts buying. In addition to which the stores also saved on energy costs. Calculations extrapolating the results to all stores throughout California revealed a potential annual return of over 47.5 million dollars and savings of 2.5 million on energy costs.

Better learning performance

To all intents and purposes, the same principles apply for schools as for any other building: in a pleasant environment, learning performance is higher, absenteeism and drop-out rates are lower. Children in classrooms with a lot of daylight and views of greenery achieved 7-18% better test results and learned 20-26% faster. Data from the NCSET (the US National Center on Secondary Education and Transition) revealed that pupils who drop out of school earn around 9,000 dollars less a year, and that if all the drop-outs of 2007 had actually finished school, this would have benefited the US national economy by an additional 329 billion dollars throughout their further career.

Well-being, house values and neighbourhood crime

Green, nice neighbourhoods are value for money. People are prepared to pay 58% more for a house overlooking water. In Cleveland, houses in neighbourhoods that were well laid out with lots of big trees proved to generate 7% higher rental income and achieve 4-5% higher sale prices. In Washington, houses next to the park are worth 5% more. Properties on the lake in Puget Sound (Washington) are worth 128% more than houses in other neighbourhoods. Sacramento conducted a survey among users of the city parks and reached the conclusion that the accessibility of the parks had generated an annual saving on medical costs of 19.8 million dollars. Parks also appear to boost social cohesion. While it is difficult to quantify “social capital” in monetary terms, in Philadelphia donations to and the value of the hours’ voluntary work carried out in the parks amounted to 8.6 million dollars. In recent years Singapore has applied a consistent greening policy, convinced that a green city will attract more investors and thus boost economic growth. Green neighbourhoods also prove to have significantly less crime. In Chicago, for instance, 52% fewer infringements and crimes were committed in properties situated in green environments; 7-8% could be linked to the better access to nature. Estimates based on these figures show a potential annual saving on crime prevention of over 162 million dollars. Access to greenery, e.g. city parks, also contributes to well-being and health. The medical costs related to obesity, accounting for some 10% of annual medical costs in the US, could be reduced substantially.

An example: Biophilic New York

If New York were to be redeveloped applying biophilic design principles, with large and small greenery in public spaces, lots of daylight and green in buildings, this could result in:

• daylight prevents pupil absenteeism: savings including 27.9 million dollars in terms of parents’ leave.
• green and healthy working environments improve productivity: benefit of 470 million.
• a pleasant, green urban environment cuts crime rates: savings of 1.7 billion on detention costs.

Business case for the Netherlands?

Terrapin’s first steps towards quantifying the economic effects of biophilic design demonstrates that in the US, organisations could save up to 2,000 dollars per employee by investing relatively small amounts in the working environment, and 93 million dollars a year could be saved on healthcare by ensuring patients have a view of greenery. Green and naturally lit retail gain, with increases in returns of 12% and 40% respectively. These are interesting figures.

No coordinated statistics are available on the financial gains to be made through the biophilic design of buildings and environments in the Netherlands. In the context of international research into The Economics of Ecosystems and Biodiversity (TEEB) initiated by the UN, wider research is being conducted into the potential effect for Dutch towns and cities. Several years ago first steps were also taken by the KPMG to determine the social and economic values of urban green on the basis of two case studies in the Bos en Lommer district of Amsterdam. Creating more green spaces in urban areas would appear to generate potential savings of 65 million euros on the public health budget. More green could also reduce absenteeism resulting in potential savings of 328 million euros.

Besides the lack of coordinated for statistics biophilic design in general, there are also no coordinated financial statistics available that relate specifically to the social returns on indoor greenery. That is a shame because many people spend the majority of their time indoors and green would benefit them in so many ways. It could be very interesting for interior landscapers to seriously consider the possibilities of quantifying the social returns on green in buildings, deducting the investment for construction and maintenance. Would it not be easier to approach financial managers of large organisations and institutions with such a business case in hand? Has the time not come for a Dutch Social Cost Benefit Analysis of indoor green?

If you’d like to know more about the social and economic benefits of biophilic design, the calculations Tarrapin applied for this study, and the underlying research read the report and other case studies at www.terrapinbrightgreen.com

Plants are capable of absorbing volatile organic compounds and converting them into nutrients. It has long been known that plants can adsorb substances with the pores on their leaves. In recent years, however, research has increasingly been focusing on the wondrous workings of plant components below ground. Roots absorb toxic substances, to a slight extent, for example. What is even more interesting is that the bacteria living in the ground, and in potting soil, detoxify the air day and night.

Plants purify the air

Do you have many plants in your home? Besides being beautiful to look at, that is also very healthy. You would not think so, but volatile organic compounds (VOCs) such as benzene and formaldehyde are very common in the home. These toxic substances are found in clothes, furniture and carpets, for example, as a result of which the air quality in houses, offices and schools is often very poor. This, in turn, can cause poor concentration and headaches. It is therefore vitally important that we make our indoor climates healthier. Plants can help us do just that. Plants are known to be able to absorb these toxic substances and thus purify the air. Our waste consequently feeds our indoor plants and they give us our oxygen and clean air in return. How do plants do that? Where are the filters in a plant? Are they in the foliage, the stems, the roots, or is it the work of another, as yet unknown force?

How do leaves and stems purify the air?

For a long time, research primarily concerned the aerial components of plants. Researchers discovered pores in the leaves and stems of plants. These stomata on the foliage absorb toxic substances out of the air. The more stomata, the higher the plant scores in terms of air purifying qualities. (Read more about how plants work). This Egyptian study from 2012 reveals The Spider plant (Chlorophytum comosum) and Peace lily (Spathiphyllum) to be particularly good at absorbing volatile organic compounds from the air with their stomata, for example. Some plants even adsorb small quantities of certain toxic substances in a waxy film on their leaves. In short: above ground, plants can convert significant levels of toxic substances.

However, plants consist of more than foliage alone. In recent years, more and more researchers have also been looking below ground and examining the plant’s thus-far hidden air purifying qualities. It appears that the roots purify the air by absorbing a little of the toxic substances. However, it is primarily the bacteria and fungi living around the roots (the micro-organisms in the rhizosphere) that work themselves crazy to convert the majority of the toxic substances to harmless compounds.

Soil life as air purifying champion

In a South-Korean study from 2008 into how aerial and root-zone parts of plants contribute to the removal of formaldehyde, two species of pot plants were compared day and night. The plants were placed in sealed chambers, where they were exposed to a specific quantity of this toxic substance. The below-ground plant components, the root zone, proved by far to absorb the most toxic substances. This is because the micro-organisms in the root zone do not only work in daylight; they carry on working through the night. While a plant’s leaves take a nap, so to speak, the fungi and bacteria in the soil continue to purify the air. In other words: in daylight a plant’s leaves are also hard at work and soil life then counts for 50% of the air purification (1:1). The night-time ratio is very different, however. The leaves then do practically nothing at all whereas the microorganisms in the soil carry on working just as hard, if not harder.

Bacteria everywhere

This night-time working of bacteria was not the only interesting discovery about soil life. Research by Wolverton in 1993 revealed that the longer the microorganisms are exposed, the more they improve their detoxifying ability. So not only do they work 24/7, they also improve their ability to remove toxic substances from the indoor climate.

Some bacteria do not actually purify the air themselves; they help the plant to degrade the toxic substances more effectively, as it were. Other bacteria do degrade the toxic substances themselves. As many as 7 different bacterial strains were found on the Golden Pothos plant, for example. One of these bacterial strains proved capable of removing 86% of the toxic substance formaldehyde from the air within 24 hours.

Plants and microorganisms live in mutual dependency. The plants supply the bacteria and fungi with sugars and the soil life supplies the plants with minerals and other nutrients in return. Plants secrete a certain sap that attracts bacteria, which is why between 100 and 1000 times as many bacteria are found in the rhizosphere than in soil with no vegetation. This applies to the soil in your garden, but also to the potting soil your indoor plants are growing in. Furthermore, these saps encourage bacteria in the rhizosphere to improve the biodegradation of soil pollutants.

PM: Particulate Matter VOCs: Volatile Organic Compounds IAP: Indoor Air Pollution Source: www.mdpi.com

Did you know that bacteria do not only live below ground but that the stems and leaves of plants are also covered with these invisible air purifiers? In 2015, a Belgian-Polish study specifically examined these air-purifying interactions between plants and microbes. The researchers concluded that there is tremendous unused potential in the symbiosis between plants and such microbes as bacteria and fungi. They called this purifying effect of plants phytoremediation: the use of plants to clean up contaminated sites.

How does phytoremediation work?

There are several ways in which plants and their soil life can purify their environment. Some plants are capable of absorbing harmful chemicals from the ground and groundwater and removing or converting them. Other plants can purify water or air.

Diagrammatic representation of microorganisms working on or near a plant to purify the air: phytoremediation. (source: www.mdpi.com)

Plants can help reduce contamination through various natural processes:

• Plants can immobilise pollutants in the roots, stems and leaves (photostabilisation).
• They can convert harmful substances into less harmful substances inside the plant or in the rhizosphere.
• They can convert harmful substances to gasses which they release into the air.
• They can immobilise harmful substances on their roots, where they are then broken down by micro-organisms such as bacteria and converted to less harmful substances.
• Plants and their bacteria are also able to absorb volatile organic compounds from the air, thus improving the air quality.

Source: https://clu-in.org/download/Citizens/a_citizens_guide_to_phytoremediation.pdf

Back to indoor plants

Potted plants do not usually come into contact with contaminated ground or groundwater. Most important with regard to the indoor climate, therefore, is that the last natural process of phytoremediation is applied: air purification. Soil life is essential to this process.

A plant living in symbiosis with certain bacteria and fungi can contribute significantly to clean air and a healthy (indoor) climate, and to clean soil and water as well. The foliage, stems and roots all do their best, but really good results are not achieved until the fungi and bacteria join in the process. Micro organisms such as bacteria, both below and above ground, are the absolute champions in detoxifying their environment. Phytoremediation is consequently a promising technique used to remedy contaminated environments; both indoors and outdoors.

Guest author: Marjolein Bezemer

Please save the date! Our annual EILO excursion 2019 will take place on October 3-4 in Paris.

There will be workshops, presentations, visits and the announcement of the winners of the EILO Award in the categories Plant Walls, Stand Alone, Interior Landscaping and Artificial Greenery.

From May 15 the competition will be open for entry!